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Harvest Weed Seed Control

Thu, 12/13/2018 - 12:36

While herbicide resistance is not a new issue, the rapid increase in multiple resistant biotypes in waterhemp, giant ragweed, and horseweed (marestail) is limiting herbicidal options. A waterhemp biotype resistant to six herbicide groups (2, 4, 5, 9, 14, and 27) was recently identified in Missouri. The majority of Iowa fields have waterhemp resistant to three herbicide groups, and five-way resistant populations have been found.  While herbicides will remain the backbone of weed management systems for the foreseeable future, it should be clear that additional tactics are needed.  This article focuses on alternative strategies that fit our current cropping system, with an emphasis on harvest weed seed control (HWSC). While none are as easily adopted as changing herbicide programs, they will be essential for preserving herbicides as effective management tools.

Identifying weak links in a weed’s life cycle

Summer annuals are the dominant weed problem in the corn-soybean rotation since these pests establish and mature at the same time as the crops.  The annual life cycle has several distinct stages, the success at transitioning between these stages determines whether a weed increases or decreases within a field (Figure 1).  Population dynamic models allow researchers to investigate how control tactics targeting different ‘choke points’ influence the long-term success or failure of a weed. 

Current weed management programs primarily target weeds as they emerge from the seed bank (preemergence herbicides) or as they develop from seedlings (postemergence herbicides).  While these tools are highly effective, the increase in herbicide resistance raises concern regarding their sustainability.  Population dynamic models reveal that weeds are very sensitive to changes in the number of seed that enter the seed bank, thus tactics that reduce seed production or their entry into the seedbank have a large impact on the long-term success of the weed.  A population model evaluating the benefit of HWSC in delaying the onset of resistance showed that destroying approximately 50% of weed seed at harvest delayed resistance evolution by nearly 10 years (Somerville et al. 2018).

Harvest weed seed control (HWSC)
Preventing seed produced by weed escapes from entering the seed bank is an effective approach to weed management.  The first mechanized combines often were equipped with weed seed collectors to prevent weed seed from being returned to fields.  Walking beans was a rite of passage for generations of Iowa farm kids. However, with the introduction of modern herbicides and increases in farm size, these tactics have fallen out of favor. HWSC is one of the few alternatives to herbicides that can be incorporated within Iowa’s production system without significantly increasing labor requirements.

The interest in HWSC has been driven by Australia’s struggle with herbicide resistant weeds.  Western Australia is recognized as the herbicide resistant weed capital of the world due to the widespread occurrence of multiple resistant weeds.  The loss of effective herbicides for several important weed species, especially annual ryegrass (Lolium rigidum) in wheat production, has forced the development of innovative approaches to managing weed seed before they enter the seedbank.  A survey of Australian farmers in 2014 found that 82% of respondents expected to use some form of HWSC within 5 years (Walsh et al. 2017).

Australians have developed several HWSC techniques, including chaff carts, baling of crop residues, chaff tramlining, narrow-windrow burning, and weed seed destruction (Walsh et al. 2017).  Narrow-windrow burning is the most widely used HWSC practice in Australia (Table 1).  This strategy involves altering how the combine manages crop residue during harvest (Walsh and Newman 2007).  Relatively simple modifications are made to concentrate the chaff in a narrow windrow that is later burned.  Research has shown that 70 to 80 percent of weed seed is collected by the combine and concentrated in the chaff, and nearly all of these seeds are killed by fire.  The use of this practice in Western Australia has increased from 15% of farmers in 2004 to more than 50% of farmers in 2014. Due to differences in crops and climate, this tactic may not be effective in Iowa, but its widespread adoption demonstrates the value of targeting weed seed at harvest.

Probably most applicable for Midwest cropping systems are chaff mills, devices that destroy weed seed during harvest (Schwartz-Lazaro et al. 2017). Chaff, which contains the majority of weed seed, is separated from other plant material as it moves through the combine. The chaff is run through a rolling cage mill that damages seed sufficiently to render them non-viable. The original design, the Harrington Seed Destructor, was a separate unit pulled behind the combine.  More recently, chaff mills are integrated into the back of the combine. 

Factors that influence the effectiveness of chaff mills are how long seed are retained on weeds and the ability of the mill to destroy seed.  Seed retention varies widely among species. Chaff mills or other forms of HWSC would have little value for managing giant foxtail since most seeds fall from plants prior to harvest.  Weed scientists at the University of Illinois found that 72, 92, and 95% of waterhemp seed remained on the plant at the time of soybean harvest in three years of research (A.S. Davis, unpublished data).  The value of HWSC for waterhemp would be diminished in years with late harvest, such as in north central Iowa in 2018.  Tests with a wide range of weed seeds have shown that greater than 95% of seed entering the mill is rendered non-viable, thus retention on the plants is the limiting factor in the effectiveness of this tactic.

Destroying weed seeds with combine modifications, therefore reducing the return of seeds to the soil weed seedbank, is an effective way of reducing herbicide selection pressure and the resultant evolution of herbicide resistant weeds.  But as they say, there is no free lunch.  Early versions of chaff mills cost approximately $120,000, but people estimate that with mass production the cost could be reduced by at least 50%.  In addition to the cost of the equipment, there are several factors that pose challenges to this technology. Current versions require approximately 80 to 100 horsepower, this power drain can result in a 12-20% reduction in combine capacity (Anonymous 2018).  The increased power requirement associated with weed seed destruction results in an average increase in fuel consumption of 0.4 gallon per ton of grain.

Currently there is limited experience using the chaff mills in corn or soybean, thus it is unclear how well they will perform in our system.  Green stems of crops and weeds negatively impact mill performance, frequently blocking flow of the chaff through the mill.  The University of Arkansas has the only integrated chaff mill in the United States, and they report that it has worked better in corn than in soybean.  The problems in soybean likely are associated with the green material frequently present during soybean harvest.

Another issue with the chaff mills has been rapid wear of the mill components.  Manufacturers estimate that rotors should have a useable life of 800 hours, but most Australian owners of the equipment report lives of less than half that.  Replacement cost for rotors is more than $2000.  The low cutting height of soybean probably would reduce the lifespan of rotors more than when harvesting corn due to greater amount of soil on the soybean residue.

At this time, most Iowa farmers would not consider weed management a big enough problem to warrant the expense and inconvenience of adopting HWSC.  Australia’s farmers went this route only after weeds developed resistance to nearly all herbicides available for their cropping system.  The increasing pace of herbicide resistance evolution and the slow introduction of new herbicide sites of action suggest we will face the same dilemma in the not-too-distant future.  To prevent further loss of effective herbicides, attitudes towards weed management need to change. Reducing the size of the weed seedbank must be viewed as just as important as protecting crop yields.  

There are several issues with HWSC that limit its utility in our system at this time.  However, it is important to recognize that this is new technology for which the bugs are being worked out.  Weed problems are severe enough in Australia that many farmers are willing to tolerate the problems associated with the equipment.  Currently there are only two versions of the chaff mills on the market.  At least three other companies are involved in designing new equipment; these companies have greater resources available for supporting development than the initial companies.  In addition to reducing the cost of the equipment, it is likely that some of the current limitations to the internal chaff mills will be resolved. Until HWSC is more widely available and convenient to implement, farmers must take steps to optimize both the effectiveness of herbicide programs and the suppressive ability of the crop.


Anonymous.  2018. Residue management at harvest.  Weed seed options. Kondinin Group.  Online https://weedsmart.org.au/wp-content/uploads/2018/06/RR_1802_weedsmart.pdf

Schwartz-Lazaro, L.M., J.K. Norsworthy, Walsh, M.J., and Bagavathinnan, M.V. 2017. Efficacy of the Integrated Harrington Seed Destructor on Weeds of Soybean and Rice Production Systems in the Southern United States.  Crop Sci. 57:2812-2818.

Somerville, G.J., S.B. Powles, M.J. Walsh and M. Renton.  2018.  Modeling the impact of harvest weed seed control on herbicide-resistance evolution. Weed Sci. 66:395-403.

Walsh, M. and Newman, P. 2007. Burning narrow windrows for weed seed destruction.  Field Crops Res. 104:24-30.

Walsh, M., Ouzman, J., Newman, P., Powles, S., and Llewellyn, R. 2017.  High levels of adoption indicated that harvest weed seed control is now an established weed control practice in Australian Cropping. Weed Technol. 31:341-347.


Prepared for the 2018 Integrated Crop Management Conference. Ames, IA. 

Category: WeedsTags: harvest weed seed controlherbicide resistanceAuthor: Bob Hartzler

Now is the time to replenish your crop resources for the 2019 season, with bulk deals

Wed, 12/12/2018 - 13:20

Winter has nearly arrived. The fields are harvested. Equipment has been tucked in, and the evaluation of the season is well underway. While the new year brings the promise of a great crop season in 2019, it’s important to remember that while we recharge for the winter, so do field crop pests. Make sure you’re prepared to handle all that mother nature can throw at you by stocking up on Iowa State University Integrated Pest Management (IPM) Extension publications.

Need some materials for your winter in-service or presentations? Want to make sure your staff has the most up-to-date information at the palms of their hands? With four ISU Extension publications now offered at substantial savings in bulk quantities, you can be sure that everyone is armed and ready to counter next year’s insects, diseases and weeds. ISU Extension publications are great field scouting resources and provide a wealth of information for identifying production issues in fields.



Soybean Diseases: A recently updated, 40-page compendium on the vast array of diseases that impacts soybeans, depicting foliar and below soil symptoms, scouting tips and disease treatments/prevention, across the Midwest. Guide is in full color, hi-resolution images. Also included are illustrated disease cycles for many diseases, a foliar disease estimation chart and soybean growth and development and staging information. This guide is available as single copies for $5 each, but can be ordered in boxed quantities of 50 for a reduced price of $3.50 per publication. More details here.




Corn Diseases, A recently updated, 48-page compendium on the vast array of diseases that impacts corn, depicting foliar and below soil symptoms, scouting tips and disease treatments/prevention, across the Midwest. Guide is in full color, hi-resolution images. Also included are illustrated disease cycles for many diseases, a foliar disease estimation chart and soybean growth and development and staging information. This guide is available as single copies for $5 each, but can be ordered in boxed quantities of 50 for a reduced price of $3.50 per publication. More details here.






The Corn and Soybean Field Guide is a palm-sized compendium for quick reference, perfect for crop scouts. Complete with 375 pictures, illustrations, diagrams and tables, and printed on sturdy card-stock so it’s able to weather the conditions you do. Normally $15 for a single copy. However, if you purchase a bundle of 25, you only pay $10 per copy. More details here.






The Weed Identification Field Guide 2nd Edition, much like the Corn and Soybean Field Guide, also is a palm-sized compendium for quick reference, perfect for crop scouts. Complete with 250 high quality pictures and printed on sturdy card-stock. Palmer amaranth information was added to the 108-page field guide, and information on herbicide resistance and management was updated from the first edition. Normally $10 per hard copy, is less than $8 per guide if you purchase a box of 44 copies. More details here.



Category: Crop ProductionInsects and MitesPesticide EducationPlant DiseasesWeedsHerbicide ResistanceTags: CornSoybeandiseasesIPMguidescrop scoutingInsectsAuthors: Ethan StoetzerAdam SissonCrop(s): CornSoybean

Herbicide program development: Herbicide rate calculations

Tue, 12/11/2018 - 12:47

This is part two of a four-part series originally posted in 2016 on using multiple, effective herbicide sites of action (herbicide groups) at effective rates as part of a long-term weed management system. Read part one and part two now.

It is important to use multiple, effective herbicide groups, as discussed in the previous two parts of this series. After we’ve passed those tests, it is equally important to be sure we’re using an effective rate to manage our weeds. Many herbicide products combine multiple herbicides and herbicide groups to create effective products for yield protection and ease of use. Sometimes these premixes, even when used at full label rates, will use lower rates of individual products compared to the stand alone product. 

Reduced rates of premergence products are commonly applied in order to reduce costs or reduce the risk of crop injury or herbicide carryover. While reduced rates can be effective at preventing early-season competition by controlling the first flush of weeds, they greatly reduce to length of weed control provided by the preemergence herbicide. The shorter residual control results in a larger population exposed to the postemergence program, and increases the risk for herbicide resistance to those products. The shorter residual also reduces the window for timely application of the postemergence product.

In order to evaluate the rates of your herbicides, we must compare those premixes and package products to the full rate of individual products containing only one active ingredient.  For example, you might choose to use the product Authority First for preemergence waterhemp control. This product contains two herbicide groups, 2 and 14. We know that HG 2 is not effective against waterhemp due to resistance, so my product only contains one effective herbicide for waterhemp management. I want to compare that HG 14 product, sulfentrazone, in Authority First to the full rate of sulfentrazone in a product that only contains sulfentrazone, Spartan.

When comparing two products, I need to know the application rate of each product and the concentration of the chemical in the products. This requires that I know what the herbicide label says. I like to use the resource www.cdms.net to look up product labels. The directions to find herbicide labels on this website are available in Part 1 of this series

On the first page of the herbicide label, I can find the information regarding product concentration necessary to do the math to compare rates. Most labels will have the herbicide group numbers on the first page as well.

The concentration of individual active ingredients is directly under the active ingredient information on the first page of a herbicide label.  You can see the concentration of sulfentrazone is 0.62 pounds active ingredient per pound of product.  This tells you it is a dry product.  If the product was liquid, it would be given in pounds of active ingredient per gallon of product.

Next, we need to find the application rate of the product to determine how much active ingredient is applied per acre (picture above). Consider the characteristics of your own soils when determining the full herbicide label rate. Also, be sure to use the same conditions when comparing across the two labels. I am assuming the soil will have < 3% organic matter and will be a medium-fine texture. The appropriate full label rate for those conditions would be 6.45 dry ounces per acre. This label has already calculated the amount of active ingredient applied per acre: 0.25 lb sulfentrazone per acre. 

Next, I need to find the herbicide with sulfentrazone as the only active ingredient to compare this rate to. That product is Spartan.

Again, you can see this herbicide label is set up similarly to the previous one. It contains the herbicide group number for the product and the concentration of the active ingredient directly below the list containing the active ingredient.

You’ll see this concentration is noted in pounds of active ingredient per gallon since it is a liquid product.

Again, I’m going to assume my soil has more than 1.5% but less than 3% organic matter and is a medium to fine texture. I just need to make sure I am comparing rates of the two products (Authority First and Spartan) for the same soil type. I can apply 10.1 fluid ounces of product per acre. How much sulfentrazone is in those 10.1 fluid ounces? 

Time to break out the pencil, paper, and calculator. I like to lay the math out as shown below. I first convert the fluid ounces to gallons, since the concentration is in pounds per gallon.

A full rate of Spartan has 0.316 lbs of the active ingredient sulfentrazone, while a full rate of the premix, Authority First, contains 0.25 lbs of the active ingredient sulfentrazone.  Authority First has about 79% of a full rate of sulfentrazone.

What does this mean for my preemergence herbicide application? Ideally, the rates applied in premix products should be the same as the single active product. However, manufacturers frequently reduce the rate assuming there will be additive action among the active ingredients or in order to reduce costs. How much of a reduction in the applied rate is ‘acceptable’ is subjective, but I would like to use at least 75% of a full rate. In this example, the second active ingredient in Authority First will not help in controlling waterhemp, so you are relying solely on the reduced rate of sulfentrazone to control this weed. 

It’s important to do this math yourselves. You will then be more aware of the expected period of weed control with a preemergence herbicide program and able to make better management decisions based upon that knowledge. You also may have the ability to ‘spike’ your preemergence herbicide application with more active ingredient to reach that 100% full rate, if the label allows.

Category: Herbicide ResistanceTags: herbicide resistanceherbicide labelsherbicide resistant weedsherbicide groupscalculating ratesresistant waterhempwaterhempAuthors: Meaghan AndersonBob Hartzler

Herbicide program development: Using effective herbicide groups

Tue, 12/04/2018 - 08:25

This is part two of a four-part series originally posted in 2016 on using multiple, effective herbicide sites of action (herbicide groups) at effective rates as part of a long-term weed management system. Read part one now.

After you've started working on a program that contains multiple herbicide groups (sites of action), you need to make sure you're using multiple herbicide groups that will be effective against your target weeds. For most people, the target weed will be waterhemp. Others may have problems with giant ragweed, horseweed, or other weeds. Waterhemp is the target weed in my example, but consider what your most problematic weeds are to run through this exercise for yourself.

Things to consider when determining whether a herbicide is effective against your target weed include (1) whether the herbicide is labeled to control the weed and (2) whether your target weed is resistant to the herbicide group.

Let's look at herbicides as if waterhemp is the weed that causes us the most issues. Here's a table of herbicide groups used in Iowa crops.

Herbicide Group Number Site of Action Herbicide Group Number Site of Action 1 ACC-ase 10 Glutamine synthetase 2 ALS 13 DPX synthase 3 Tubulin 14 PPO 4 Auxinic binding sites 15 Unknown (long chain fatty acid synthesis) 5 D1 protein 19 Unknown (Auxin transport) 6 and 7 D1 protein 22 Unknown (Photosystem I inhibition) 9 EPSP synthase 27 HPPD

The table looks to contain a lot of options, but when I consider that my target weed is waterhemp, I can start removing choices and find I only have nine HG choices for waterhemp control in corn and soybean.

  • HG 1 consists of only grass-killing herbicides.
  • HG 6 and 7 are not commonly used in these crops, and they have limited activity on waterhemp.
  • HG 13 (clomazone) is labeled for use in soybean, but provides unacceptable waterhemp control.
  • HG 19 contains one chemical, diflufenzopyr, is only used in combination with dicamba in herbicide premixes. This chemical does not provide waterhemp control alone.
  • HG 22 includes paraquat, a non-selective contact herbicide, which could only be used prior to crop planting or as a crop desiccant. It would control emerged waterhemp, but due to its non-selectivity, it could not be used to kill weeds in an established corn or soybean crop.
Herbicide Group Number Site of Action Herbicide Group Number Site of Action 1 ACC-ase 10 Glutamine synthetase 2 ALS 13 DPX synthase 3 Tubulin 14 PPO 4 Auxinic binding sites 15 Unknown (long chain fatty acid synthesis) 5 D1 protein 19 Unknown (Auxin transport) 6 and 7 D1 protein 22 Unknown (Photosystem I inhibition) 9 EPSP synthase 27 HPPD

After I removed some herbicide choices due to lack of activity or usefulness against waterhemp, I need to consider what my waterhemp population looks like. Do my fields have any herbicide resistances? Weeds that are currently known to be resistant in Iowa can be found at http://weedscience.org/. Iowa has biotypes of waterhemp resistant to HG 2, HG 5, HG 9, HG 14, and HG 27.

Most waterhemp in Iowa are resistant to HG 2, so I know those herbicides won't kill my waterhemp. I know that the presence of other resistances in my fields depends highly on the history of herbicide use. For example, if I've heavily used products from HG 14 postemergence in soybean in my battles with waterhemp, and it seems these products are providing less consistent waterhemp control than in the past, there is a good possibility that the waterhemp in my field is resistant to these herbicides. I should be careful about continuing my reliance on those products and need to look for other options - possibly glufosinate (HG 10) - as options against waterhemp. 

The presence of resistant waterhemp will vary from field to field, often based on individual management tactics used by farmers.  Waterhemp is very efficient at accumulating multiple resistances. In Iowa, at least one population has been identified that is resistant to group 2, 5, 9, 14 and 27 herbicides. It is important to determine what herbicide groups you have relied on for managing waterhemp in the past on your farm(s), and then carefully evaluate if they are still controlling weeds as effectively as in the past. What herbicides are your waterhemp surviving?

After analyzing all herbicide options, I see we only have FOUR herbicide groups that are effective against waterhemp and that waterhemp (in Iowa) is not known to have developed resistant to: Groups 3, 4, 10 and 15.  However, HG 4 resistant populations of waterhemp have been identified in Nebraska and Illinois.  In addition, a close relative of waterhemp, Palmer amaranth, is known to have populations resistant to HG 3. Resistance is a possibility with any herbicide. 
As you plan for your herbicide program next year, make sure you're including multiple sites of action that are effective against your target weeds. Evolution of herbicide resistance is inevitable in plant populations when we rely on these tools, but we can delay resistance problems by using multiple, effective herbicide groups. 

Resources Available:

Are your herbicide groups effective against your target weeds?

Category: Herbicide ResistanceTags: herbicideherbicide programherbicide resistanceherbicide resistant weedswaterhempresistant waterhempAuthors: Meaghan AndersonBob Hartzler

Herbicide program development: Using multiple sites of action

Tue, 11/27/2018 - 12:56

This is part one of a four-part series originally posted in 2016 on using multiple, effective herbicide sites of action (herbicide groups) at effective rates as part of a long-term weed management system.

With the stagnant development of new herbicides and weeds seemingly evolving herbicide resistance faster than ever before, it's important to maximize the usefulness of every herbicide application. A new herbicide site of action (or herbicide group number) for use in corn and soybean production has not been discovered since the early 1980s. According to Dr. Ian Heap with www.weedscience.org, since the 1980s, the confirmed number of unique cases of herbicide resistance globally is increasing at a rate of about 12 discoveries per year.

To delay resistance problems as long as possible and assure our herbicides retain their value, we must 1) use multiple herbicide sites of action that target our problem weeds. This is more complicated than simply designing a program with multiple sites of action. We must also 2) assure the different sites of action are effective against the problem weeds we are fighting, and 3) make sure the herbicides are used at effective rates and applied at the right time to provide maximum control. Finally, we must realize that herbicides put significant selection pressure on our weed populations, making herbicide resistance development an inevitable outcome of using herbicides. Thus, 4) a more diverse system of fighting weeds is necessary for long-term success, including non-herbicidal options as much as possible.

The first step in planning a herbicide program and battling herbicide resistance is to make sure your program includes multiple sites of action or what we will refer to as herbicide groups.  The herbicide site of action is the specific molecule that the herbicide binds to; this binding disrupts a biological process (the mode of action) and results in the death or injury of the plant. The site of action is a specific subset of the herbicide mode of action. The mode of action is the biological process that is affected by the herbicide, e.g. photosynthesis, amino acid synthesis. Important herbicide sites of action and their corresponding herbicide group numbers are listed below (Table 1).

Table 1. Important herbicide group numbers for use in corn and soybean production. Herbicide Group Number Site of Action Herbicide Group Number Site of Action 1 ACC-ase 10 Glutamine synthetase 2 ALS 13 DPX synthase 3 Tubulin 14 PPO 4 Auxinic binding sites 15 Unknown (long chain fatty acid synthesis) 5 D1 protein 19 Unknown (auxin transport) 6 and 7 D1 protein 22 Unknown (photosystem I inhibition) 9 EPSP synthase 27 HPPD

Herbicide groups are a relatively new way of determining the site of action of the myriad herbicides on the market. Each site of action has been assigned a number, and most herbicide labels prominently display this group number on the product label. If a product includes two different sites of action, the label will have two different group numbers listed. Keeping track of the herbicide group numbers is the simplest way for farmers to keep track of the different sites of action they’re using in their herbicide program.

If you don’t have your herbicide labels on hand, one handy website to look up pesticide labels is www.cdms.net. After clicking on the label database section as shown below, I can look up the product by brand (trade) name or manufacturer. When I find the product I was looking for, I can click on the link called ‘specimen label’ to bring up the product label.

I am able to pull up a PDF copy of the label, and I can even use the CTRL+F function to bring up a search bar and find a particular word or phrase I’d like to find.

Note the herbicide group numbers listed on the first page of the Authority First herbicide label. Most, but not all, herbicide labels will display the group numbers in this way.

Here are some additional excellent resources to find additional information needed to develop effective herbicide programs.

Download the most recent Herbicide Guide for Iowa Corn and Soybean Production to look up herbicide group numbers for products with only one active ingredient or group numbers for premixes with multiple herbicide group numbers.

Use the Take Action on Weeds herbicide site of action chart, if you’d prefer to see everything grouped on one page. You can print it for your office as well!

The Take Action on Weeds website also includes a page for looking up herbicide group numbers by either trade name or active ingredient. If you know your herbicide trade name, just type it in to find the group numbers that product contains!

So, how well are you fighting off herbicide resistance?

Category: Herbicide ResistanceTags: Weedsherbicidesherbicide resistant weedsherbicide resistanceherbicide groupsherbicide programAuthors: Meaghan AndersonBob Hartzler

2019 Soil Health Conference Registration Now Open

Tue, 11/13/2018 - 15:23

Soil health is the foundation for a vibrant and strong agriculture system and economy. Healthy soils are essential to healthy environments including clean air and clean water for sustainable agriculture and livelihoods. The 2019 Soil Health Conference will be held in Ames at the Scheman Building at Iowa State University on February 4-5, 2019. Registration is now open. This conference is organized by Iowa State University Extension and Outreach, the College of Agriculture and Life Sciences and the Department of Agronomy. The 2019 theme is “Science Meets Practice for Advancing Soil Health” in Iowa and the Midwest.

This two-day soil health conference will host a number of renowned scientists, agronomists, framers, and conservationists as conference speakers. Presentations at the conference will address concerns and interests of farmers, agronomists, agricultural consultants, soil scientists, extension professionals, and policy makers who are interested in learning about soils for sustainable agriculture.

During the two-day conference, research-based information addressing the soil health principles and management practices in decision-making for building healthy soils, sustainable agriculture, and a clean environment will be presented. Panel discussions led by farmers, agronomists, and scientists along with a new and unique session where attendees can “Ask the Experts” will be included. This information will be provided by scientists from Land-grant universities, USDA-ARS, USDA-NRCS, farmers and leaders in the agriculture sector. Posters on research and education addressing management practices and their effects on soil health will be displayed during the two days conference.

This conference will provide an opportunity for certified crop advisors who are eligible to earn continued education credits in soil and water by attending many of the breakout sessions. Program, invited speakers and registration information can be found on the conference website. Registration is currently open and we look forward to see you February 4- 5, 2019 for the conference. Don’t miss the opportunity to learn more about soil health and develop a network with other industry professionals.

Category: SoilsSoil ManagementTags: soil healthsoil health conferenceAuthor: Mahdi Al-KaisiCrop(s): CornSoybeanCover Crop

Precision Pesticides

Sat, 11/10/2018 - 23:15

Pesticides are substances that are designed to control pests. Every year, nearly six billion pounds of pesticides are applied worldwide. In agricultural fields, they can be sprayed, injected into the soil, or added to the seed.

There are different kinds of pesticides, named after the pests they attack: insecticides act on insects, herbicides on plants, fungicides on fungi, rodenticides on rodents, etc. Older pesticides had broad targets — they could harm insects, plants, birds, and mammals. However, newer pesticides are largely effective only against some species. For example, neonicotinoids, the most commonly used insecticides in the world, are quite safe to mammals. However, they are unable to distinguish between insect pests that damage crops and beneficial insects like bees that pollinate crops. Hence, modern-day pesticide manufacturers must increasingly find ways to harm the pests while keeping the rest safe. This can be achieved in two ways:

1. The pesticide should be toxic only to pest species


2. Non-pest species should not be exposed to the pesticide

Described below are three emerging pest management technologies trying to achieve this goal: CRISPR/Cas 9, RNAi, and nanopesticides.

1. CRISPR/Cas9 system is found naturally in bacteria. Bacteria use it to defend themselves against invading viruses. Scientists now harness this defense to modify the properties of an organism, either by shutting down the organism’s genes or introducing foreign genes into it (Fig. 1). As genes are unique to every species, this technology can be species specific. It also causes the altered genes to be passed down to future generations.

Scientists recently used CRISPR/Cas9 to disrupt a gene necessary for female development in the spotted wing Drosophila, a fruit pest. This caused the female flies to die early. However, such modified organisms are currently not released into the wild because it is not known if any unintended effects could occur. For example, other organisms of the species could gain resistance to this technology by slightly changing their DNA. Or CRISPR/Cas9 could shut down the wrong gene or act on non-pest species with similar genes.

Figure 1. A CRISPR-Cas9 system can be used to either a) prevent an important protein from being formed or b) create a protein which is deadly to the organism.

2. RNA interference (RNAi) system has been observed in many non-bacterial species, including plants and animals. It is also used as a defense against viruses. RNAi shuts down RNA; the DNA and genes are unaltered. When an organism’s RNA is shut down, it can no longer form protein and could kill an organism. For example, scientists developed corn which contain RNAi that targets western corn rootworm. When the pest ingests the corn, they can no longer form a critical protein and most die within 12 days.

As RNA is formed from genes, this technology is also species specific. It has similar drawbacks to CRISPR/Cas 9 but its effects are limited to one generation as modified RNA cannot be passed down to the offspring. Its persistence and movement in the environment are largely unknown.

3. Nanopesticides are pesticides which are incorporated within nanoparticles. Nanoparticles are very small molecules (billionth of a meter) that are usually made from metals. As smaller-sized particles cover a larger surface area, lower rates of nanopesticides would need to be sprayed in the field. Also, a greater surface area increases contact with pests. Nanopesticides do not break down easily. Thus, unlike traditional pesticides, they need not be applied frequently. And potentially, they could be encased in capsules that penetrate and enter pests more effectively than non-pest species. These properties could lower overall amounts of pesticides in the environment and/or reduce exposure to non-pests.

Nanosilver, the first nanopesticide, has been applied in plants to reduce rates of fungal root diseases. However, there are several unresolved issues. Since nanopesticides are more stable, they could persist in the environment for longer than required. And we do not know how they move - for example, do they stick to crops or do they slide off it and enter the soil or water and affect other organisms?

Category: Insects and MitesTags: pesticidesgenetic modificationAuthor: Niranjana Krishnan

New dicamba restrictions

Thu, 11/01/2018 - 07:31

I feel obligated to write something about EPA’s dicamba announcement, but will confess at this time I still have several questions that I’m seeking answers for.   But here are my initial thoughts regarding the new approach to dicamba management.

1.  45 days after planting.  I’m not sure if this restriction replaces the previous restriction that limited applications up to and including the R1 soybean stage.  Regardless, I see very little value to this new restriction. According to USDA-NASS Crop Progress reports, the 5-year average for Iowa soybean planting is 51% planted on May 20. Thus, applications would be allowed into July for much of Iowa’s soybean acres.  In 2017, 90% of dicamba misuse complaints to IDALS were associated with applications made after June 15. I believe a date restriction would be more appropriate, a date in mid-June would be my preference.

2. Certification status.  Persons under the supervision of a certified applicator will no longer be allowed to apply dicamba on Xtend soybean.  In 2017, the breakdown of applicators responsible for misuse complaints in Iowa from dicamba on Xtend soybean was 22%, 40%, and 38% for certified commercial, certified private, and uncertified private applicators, respectively. I don’t know what percentage of the Xtend beans were sprayed by the various classes of applicators (i.e. did commercial applicators spray 80% of the dicamba on Xtend crops), but these numbers don’t suggest the classification of applicator has a big influence on the likelihood of off-target movement.  The new products were changed to Restricted Use for 2018, so uncertified applicators could not apply dicamba on Xtend soybean in 2018.

3. Endangered species.  I assume this restriction will pertain to both plants and animals.  Iowa doesn’t have any plants listed as endangered, there are five species classified as threatened.  However, there are several animals listed as endangered, and a quick perusal of the list suggests the majority of Iowa counties have at least one endangered species. Thus, if animals are included in this restriction most fields in Iowa would require the 57-foot buffer along field edges (the 110 ft downwind buffer is still in play regardless of endangered species).

4.  Application hours.  The previous labels restricted applications to between sunrise and sunset, this has been further restricted to 1 hour after sunrise and 2 hours before sunset.  This restriction is intended to prevent applications during inversions.  In Iowa I know spraying in inversions has been a problem, but I don’t believe it is a leading cause of off-target movement and injury.  This further restricts time available to apply dicamba, making it increasingly difficult to apply the product legally.

As I’ve said before, the EPA is in a very difficult position in regulating this technology – whatever they do is going to be criticized by some people. Unfortunately, I don’t think these new restrictions will have a significant impact on the problems we've seen the past two years.  I was hoping for something similar to what Minnesota did in 2018, a date and temperature cutoff for dicamba applications on Xtend soybean. The Iowa Department of Agriculture and Land Stewardship can develop more restrictive approaches to managing dicamba, and I hope they will take this approach.

Category: WeedsTags: dicambaEPAXtendAuthor: Bob HartzlerCrop(s): Soybean

Milkweeds, Monarchs, and Crop Production

Wed, 10/31/2018 - 13:05

While the monarch butterfly is a globally distributed species, the eastern United States population is renowned for its annual migration from the breeding range in the northeastern United States (and Canada) to overwintering sites in central Mexico.  Overwintering populations of this cohort have declined by approximately 80% over the past twenty years.  Several factors are believed to contribute to the decline, including logging at the overwintering sites, climate change, and changes in land use and agricultural practices in the summer breeding range.  In 2014 the United States Fish and Wildlife Service was petitioned to list the monarch as an endangered species, and a decision is expected in mid-2019.  Iowa is in the center of the region where the greatest number of migrating adults are produced.  Classification of the monarch as endangered could have significant ramifications to Iowa agriculture since the Endangered Species Act provides for conservation of both the endangered organism and its habitat.

The Iowa Monarch Conservation Consortium was formed in 2015 to establish a scientific foundation for monarch conservation efforts.  The consortium is a partnership of farmer and conservation organizations, state agencies, industry and Iowa State University.  The Agronomy Department has supported research investigating the impacts of crop production on monarch reproduction, and methods to enhance the landscape to support monarchs.

The elimination of common milkweed from crop fields in the Cornbelt is frequently cited as the primary cause of the monarch decline by many monarch researchers.  Surveys of Iowa crop fields found nearly a 90% reduction in the number of corn and soybean fields infested with common milkweed between 1999 and 2009 (Hartzler, 2010).  Although the cause of this decline in common milkweed can’t be determined with the methods used, the widespread use of glyphosate following the introduction of glyphosate resistant crops likely played a major role in the loss of cropland milkweed. 

Conservation plans for protecting the monarch call for doubling the quantity of milkweed in the monarch’s breeding range.  This strategy assumes that milkweed in crop fields was an important resource for monarchs; however, there is little data to support this assumption.  Common milkweed is a perennial able to survive many of the herbicides used in crop production, but these herbicides cause significant injury to the foliage.  We suspected herbicide injury would reduce the suitability of common milkweed for monarch reproduction.  Experiments were designed to determine if damage associated with postemergence herbicides affected ovipositing preference or larval survival rates.  We found that fomesafen, a commonly used postemergence in soybean, caused severe necrosis and loss of common milkweed leaves contacted by the spray. However, injured plants resumed normal growth shortly after application, and monarch utilization of treated milkweed was similar to plants not exposed to fomesafen (Table 1).  Our research supports that milkweed in crop fields can be a resource for monarchs, but it is unlikely that common milkweed will return to earlier densities in crop fields under current crop production practices.

Table 1. Effect of postemergence fomesafen applications on utilization of 
common milkweed in soybean fields. Lizotte-Hall and Hartzler, 2018.  

Treatment Eggs/patch Number of instars (stage)/patch     1st 2nd  3rd 4th 5th Control 43.1 7.3 3.8 0.6 0.2 0.1 Fomesafen 47.3 7.8 3.1 0.8 0.1 0.1

Patches of 5 plants per 3 sq ft were established in soybean.  
No differences between treatments in egg or instar numbers. 


Significant efforts are being made by both government and private organizations to diversify the landscape in the reproduction range to increase available resources for monarchs.  The expense of converting areas not eligible for government programs (e.g. CRP, CREP, etc.) to diverse plantings of native plants may be cost-prohibitive for many farmers/landowners.  We evaluated a low-cost alternative to enhancing the diversity of non-cropped areas present on most Iowa farms.  Smooth sod brome was suppressed with low rates of glyphosate and then the areas were seeded with common milkweed and other forbs.  While suppressing brome with glyphosate increased recruitment of forbs, competition from the perennial sod resulted in very low establishment of the native plants.  New England aster and golden alexander were more successful at establishing than common milkweed. Additional work should investigate additional techniques to suppress sod without increasing the likelihood of invasion of areas by weeds.

The decline of the monarch population is complex issue.  Iowa’s agricultural community will need to participate in restoration efforts for the monarch due to the importance of Iowa to monarch reproduction, and because the majority of Iowa’s land is involved in crop production.  It is unrealistic to expect farmers to adjust management practices to allow increased survival of common milkweed in crop fields.  Thus, research is needed to determine how to best modify areas outside of crop fields to support monarch reproduction and survival. 

This article was originally prepared for a presentation to  the Department of Agronomy’s Baker Council.  The research reported was part of Sidney Lizotte-Hall's M.S. research.

Hartzler, R.G., 2010. Reduction in common milkweed (Asclepias syriaca) occurrence in Iowa cropland from 1999 to 2009. Crop Prot. 29, 1542-1544.

Lizotte-Hall, S.E. and R.G. Hartzler. 2018.Effect of postemergence fomesafen application on common milkweed (Asclepias syriaca) growth and utilization by monarchs (Danaus plexippus).  Crop Prot. 116:121-125.



Category: Crop ProductionTags: common milkweedmonarchmonarch butterflyfomesafenAuthor: Bob Hartzler

Sporebuster, a White Mold Fungicide Value Calculator

Fri, 10/26/2018 - 14:04

The follow-up to this summer's 'Sporecaster' smartphone application, designed to help farmers predict the need for a fungicide application to control white mold in soybean, is now available for download.

While Sporecaster can help farmers evaluate their risk for white mold using infection data integrated with weather patterns, whether or not to apply a fungicide can pose and economical dilemma for farmers that they might not be able to evaluate on their own.

'Sporebuster,' made from the same researchers and specialists at University of Wisconsin-Madison that brought you Sporecaster, helps farmers evaluate the cost benefits of applying a fungicide to prevent white mold. Growers enter their expected soybean price, expected yield, and treatment cost. Sporebuster instantly compares ten different treatment plans at once to determine average net gain and breakeven probability of each. 

The app is available for download on both iOS and Android.

Category: Plant DiseasesTags: white moldSoybeansporebusterfungicideAuthor: Ethan StoetzerCrop(s): SoybeanVideo: 

Harvest loss in difficult conditions

Thu, 10/18/2018 - 15:26

The 2018 Iowa harvest is posing many challenges. Higher than average harvest losses are likely due to excessive soybean shatter, flooded and wet field conditions, and lodged corn and beans.

Harvest losses can only be managed if you know where and why they are occurring. Measuring harvest loss requires stopping the combine in the field, backing up 15-20 feet, and counting lost beans or kernels in a measured area on the ground.  ISU bulletins PM 573 (Profitable Soybean Harvesting) and PM 574 (Profitable Corn Harvesting) offer guidance on measuring, evaluating, and managing harvest losses.

Soybean shatter has been identified as a particular concern this year. Faster reel speed is often associated with increased shatter loss. Try reducing reel speed if shatter loss is excessive. Unfortunately, reduced reel speed can also make it difficult to gather lodged stems. Both challenges may be present in the same field this year.

Michigan State University Ag and Soybean educator, Michael Stanton, offers this additional advice on harvest settings and management for lodged soybeans:

  • Decrease your ground speed to 2.5 to 3 miles per hour.
  • Increase the reel speed in relation to the ground speed incrementally to the point that the lodged plants are being cut and gathered into the combine without beating the beans out of the pods.
  • Position the cutter bar as close to the ground as possible.
  • Angle the pickup fingers on the reel back slightly to more aggressively pull the lodged plants to the cutter bar. Reduce the angle of the fingers if the plants are riding over the top of the reel.
  • Run the reel axle 9 to 12 inches ahead of the cutter bar.
  • Contact the manufacturer for specific recommendations if using an air-assisted reel.
  • Operate the reel as low as necessary to pick up lodged plants without causing them to ride over the top of the reel. Raise the reel if this happens.
  • Consider installing vine lifters on the cutter bar if the plants are severely lodged.
  • If the plants are badly lodged in one direction, try adding vine lifters to the cutter bar and harvesting at a 30 to 45 degree angle to the direction of the lodging. If this doesn’t work, harvest all of the lodged plants in the direction opposite to way they are leaning.

Lodged corn also presents serious challenges for controlling harvest loss.  Retired ISU Ag Engineer Mark Hanna offered this advice for reducing harvest loss with lodged corn: "Slowing combine travel speed may reduce the amount of missed ears. Harvesting "against the grain" (against the direction of stalk lean) also may reduce losses. Evaluate attempted improvements by measuring losses again. Make sure ear savers on the corn head are in good condition. Keep gathering snouts as low as practical to pick up downed stalks. Gathering chains may need to be more aggressive. Place stripper bars closer together if ear butt-shelling occurs on the stalk rolls.

If many acres of severely lodged corn are present and the window of time for harvest is short, consider procuring a corn head reel or other attachments such as crop dividers or lifters. Several after-market manufacturers market reels that can be mounted over the corn head to help lift and guide stalks into the head. Check availability through dealers or the Internet. Even if a reel does not decrease losses, it may allow faster combine travel speed with similar losses, allowing harvest to proceed in a more timely manner. Crop dividers mounted on each side of the head help to lift ears into the head that might otherwise escape."

Every harvest season brings challenges. When crop and soil conditions add difficulty, it is important to keep your safety and health in mind. While harvest speed matters, take care to not rush your own actions or decisions to the point of increasing the risk of accidents or injury. Your safety and health should always be the first priority.

Category: Crop ProductionTags: combine harvesting tipslodgingsoybean shatteringAuthor: Shawn ShouseCrop(s): CornSoybean

Zahurones: FEEL Lab internship an invaluable experience

Wed, 10/17/2018 - 11:43

The college classroom teaches you a multitude of things that you probably need to know in order to make sense of the world around you. But an internship that gives you experience in that world can mean the difference of succeeding in life or just getting by. As an agricultural communications major, I wanted a job that would help me to expand my knowledge in agriculture and give me some common public relations practice. Never did I imagine at the time that I would be working at the Iowa State University Field Extension Education Lab (FEEL) this past summer. This was an internship where I spent most of my days working out in the field rather than sitting behind a computer screen. It has been an eye-opening experience for me, working in a small environment among only three other people while at the lab; but it felt like a lot more as I was able to expand my network with different agricultural companies and Iowa State field agronomists, throughout the summer. The experience was much more personalized as I had the opportunities to learn about farm practices, hands-on, discover the science and experimentation that is done for Iowa State and work with Communications Specialist Ethan Stoetzer for Iowa State’s Integrated Pest Management (IPM) program.

This summer, my original goal was to learn more applicable hands on knowledge about common issues that farmers face in the field every season. At the beginning of the season, I refreshed my knowledge through crop scouting and documenting weeds, and conducted plant staging in each of the 40-plus different test plots. Crop scouting was something that I enjoyed because solving problems and expanding my knowledge about weeds was something that I was really good at and loved to do in the field. I was able to expand upon my background knowledge since my courses as Des Moines Area Community College, especially learning the different types of grass weeds.

As interns, we also helped with experimentation plots. Some of these experiments included dropping several different species of worms into corn whorls, covering corn ear shoots with paper bags and even growing a vegetable garden and infesting the plants with aphids later in the growing season. All of these experiments gave me a greater insight to the kinds of research that is done by ISU extension specialists. Later in the summer I began learning how to drive the 770 John Deere Tractor for mowing. This was an experience that I remember because of the patience that my co-workers and boss displayed when teaching me to drive it. It was their goal to get me comfortable on that tractor from the beginning of the summer, which is one of the main reasons why this job was invaluable; because my employer wanted to help me succeed.

Throughout my internship, I had many different opportunities to learn about the types of research that were being conducted at FEEL. I categorized and learned the effects of different herbicides within plots of corn, soybeans and alfalfa. I was also taught the science behind the hybrid of BT Corn that we used for educational purposes. Among these, I had the opportunity to wash out and look through a root pit with agronomist Angie Reick-Hinz to understand root patterns in corn and soybeans.

Not only did I have this field experience, but I also had the liberty to make connections with other agronomy and plant pathology professors from Iowa State University. These connections greatly benefited my experience with this farm because I started to understand the research that was being done in these test plots, from nitrogen application, to herbicide injury to aphid infestation. I will also continue to have these connections and resources as a junior this fall at ISU majoring in agricultural communications.

This summer internship initially did not have anything to do with communications, but my employer, Warren Pierson, worked to make this internship valuable and relatable to my major. So I began working with Iowa State’s IPM program. I began working with communications specialist Ethan Stoetzer on news releases for crop management competitions that were happening at FEEL in the months of July and August. I also worked in photography and videography to document some of the sessions and workshops that happen on the farm, and integrated them into social media pages on Facebook and Twitter for Iowa State IPM and FEEL.

Overall, this was an internship that I felt held great value for my schooling and future career. Not only have I had an experience that was tailored to my major, but it was a small work environment where I could make valuable connections with agricultural professionals, as well as get my hands dirty in the fields that make Iowa what it is. But perhaps what sets this job above anything else I could have done this summer was the fact that Warren cared about the interns making the most of this job. I wasn’t always doing PR, and I wasn’t always mowing and pulling weeds. I'd like to also thank all of our specialists and agronomists for taking the time to talk to me, and push me to try things, as well as being patient and encouraging to me. This was a very diverse type of experience that I would highly recommend to any of my fellow students who are looking into a summer internship. Iowa State has helped me in more ways than one, and I feel more confident that ever for my future endeavors.  

Emily Zahurones

Category: Crop ProductionTags: FEELIPMcrop scoutingWeedsAuthor: Ethan Stoetzer

Mueller's Top 3 Soybean Diseases of 2018

Mon, 10/15/2018 - 11:01

With the 2018 growing season coming to an end, it’s time to bust out the record books and begin logging the most prevalent diseases we’ve seen this year in Iowa soybeans. It’s important to review  these diseases so that farmers, agronomists and all of our partners can make informed decisions ahead of next year’s season. These decisions include variety selection, choosing seed treatments, developing pre-germination checklists, evaluating the cost-effectiveness of a fungicide application, and cultural practices such as crop rotation. These strategies are all part of integrated pest management (IPM). While risk of many soybean diseases was low this year, future growing seasons may be different. .

1. Frogeye Leaf Spot

Daren Muller

Rounding out the top of our list is frogeye leaf spot, caused by the fungus Cercospora sojina. Back in late July/August, Iowa State researchers and agronomists began reporting the tell-tale symptoms of round-to-angular lesions, with a light tan center surrounded by a reddish-purple margin on soybean leaves.

Frogeye leaf spot’s impact on yields can vary greatly, depending on the timing of disease appearance, varietal susceptibility to disease and weather conditions during soybean reproductive stages. We won’t know the full impact of the disease on yield until harvest concludes. If the disease begins late in the reproductive stages (after growth stage R5.5), or disease severity is low, the yield impact will likely be minimal. Conditions favorable to disease development include warm, humid weather, with frequent rains that persist over an extended period of time. Several days of overcast weather can also increase the spread of the fungus. If conditions are favorable to the disease, and there are severe disease outbreaks early or just after flowering, yield losses can be up to 35 percent.

With frogeye at number one on this list, it’s important to remember that while the disease might not be impactful this year, it can become a problem in future years, due to the fact that the spores can overwinter in Iowa crop fields. The resistance gene, known as Rcs3, has been effective against all races of this fungus known to occur in North America. Crop rotation and tillage can also be effective in reducing the amount of fungus available to infect the next soybean crop. Long rotations may be necessary if the disease has been severe in a particular field. Well-timed foliar fungicide applications can effectively control frogeye leaf spot. Research shows that applying a fungicide during pod development (R3-R4), is the most effective for managing the disease. Fungicide applications are generally more profitable when disease risk is high, however.

2.     Soybean Sudden Death Syndrome (SDS)

Daren Mueller

Coming in second place this year was SDS — probably the most recognizable soybean disease in North America — caused by the fungus Fusarium virguliforme. Reports of this disease were found at Iowa State research farms beginning in mid-July. Symptoms of SDS include yellow spots between leaf veins that turn brown as the spots expand, eventually leading to defoliation. Underground, roots will be discolored and show decay (sometimes with no foliar symptoms). When soils are wet, the SDS fungus can reproduce on root surfaces, producing a mass of spores that are purple-blue in color.

As with all diseases, yield loss can vary greatly with SDS, and is dependent upon multiple factors. Cool, wet field conditions shortly after planting favor early root infections and disease establishment. Frequent or heavy rains midseason can favor early symptom expression. Yield losses can be substantial in years when susceptible soybean varieties are planted in cool, wet fields with a history of SDS and soybean cyst nematode (SCN; caused by Heterodera glycines). If symptoms develop later in the season, or weather is not conducive for disease development, yield losses can be minimal. At the research farms, soybeans were around R3-R5 when symptoms were observed. In some areas of Iowa, high volumes of rain were the typical forecast. This disease often occurs in patches. If foliar symptoms appear at or after growth stage R6, yield loss may be minimal.

While yields might not have been severely impacted, SDS can still become a problem for soybean farmers, especially in the presence of SCN, and in cases where there is no crop rotation. Because SCN causes wounds to the root system, the plants are more susceptible to the Fusarium fungus. There are no soybean varieties completely resistant to SDS, but partially resistant varieties are available. There are seed treatments that are effective, such as the fungicide fluopyram (ILeVO®, Bayer CropScience), which has efficacy against SDS. As a seed treatment, fluopyram has reduced SDS severity and protected yield on susceptible varieties, compared to a base seed treatment in several research trials conducted by extension plant pathologists in the North Central United States.

Planting partially resistant varieties does not ensure complete control of the disease, but it will minimize yield loss. It’s important to remember that weather and field conditions drastically influence disease severity. Testing your fields for an SCN number, as well as purchasing a SCN-resistant variety could delay SDS. Research shows that tillage can have an effect on reducing SDS, but research also shows that no-till can also reduce the disease.

3.     Septoria Brown Spot

Alison Robertson

Last on our list is Septoria brown spot. Brown spot is usually the first leaf disease to occur on soybean in Iowa, and may be observed on soybeans as early as the V2 stage.  Reports of brown spot began arriving in late July, when soybeans were between R3 and R4, and mostly with full pods. Unlike many foliar diseases of soybean, brown spot starts in the lower canopy and continues upwards.

Currently in Iowa, brown spot hasn’t been making much of an impact on yields. It’s a disease that’s common in many fields each year, but fungicide application will not likely be profitable unless the disease spreads into the upper canopy. The symptoms you’d observe would be small purple or brown lesions on lower canopy leaves, progressing to irregularly shaped dark brown lesions on higher canopy leaves, as well as leaves yellowing around spots that leads to foliage death. Favorable conditions for brown spot development are warm temperatures (in the 80s) and rainy weather. Considering the wet start and end of the growing season, conditions favored the disease’s development.

To stop brown spot from occurring, it’s important to know that no cultivars are resistant to the fungus. Fungicides are not recommended due to the fact that the disease’s impact on yields is minimal and fungicide application is not likely to be profitable solely for brown spot management. Rotating to a non-host crop such as alfalfa, corn or a small grain is beneficial for reducing disease.

*Honorable Mention:

White Mold

Daren Mueller

White mold takes the spot of honorable mention, due to the fact that we saw some instances in far northern Iowa, as well as some field plots in Minnesota. While conditions were not conducive to white mold this season, it’s important to be mindful of the fact that the disease is a significant problem in the north central region. The Crop Protection Network has a great disease guide for white mold that I highly recommend those interested to read. In addition, our colleague Damon Smith at the University of Wisconsin-Madison has helped develop a model predictor for white mold, that can help you make a calculated decision on whether or not to spray a fungicide for white mold.

Category: Plant DiseasesTags: Soybeandiseaseswhite moldseptoria brown spotsudden death syndromefrogeye leaf spotAuthors: Daren MuellerEthan StoetzerCrop(s): Soybean

Mycotoxins App Available

Wed, 10/10/2018 - 12:40

With all eyes now on harvested grain quality and scouting for mycotoxins as a result of ear rot, it's important that producers and agronomists have access to all the information possible, on whichever medium they prefer to use.

An application is available on both Android and iOS that can serve as a guide for naviagating the sometimes confusing world of grain quality. Mycotoxins is available for free on app stores, and presents important information about different corn ear rot pathogens that cause significant yield losses. In addition, the app provides instructions and tips that can prove valuable knowledge for farmers and corn growers, for a proper management of corn infected with mycotoxins.

This presents information about symptomology and mycotoxins produced by predominant corn ear rot pathogens, toxic effects of mycotoxins on humans and livestock and safety levels for different uses of infected grain.

The app also provides tips on storing moldy grain, ear rot management before and during harvest and scouting and testing for mycotoxins.

Category: Grain Handling and StorageTags: mycotoxinsCorngrain handling and storageIPMAuthor: Ethan StoetzerCrop(s): Corn

New Web-based WPS Train the Trainer Course Now Available

Wed, 09/26/2018 - 11:04

A web-based national Worker Protection Standard (WPS) course to qualify trainers to train both workers and handlers is now available from the Pesticide Educational Resources Collaborative (PERC). The course, available at http://pesticideresources.org/wps/ttt/course/index.html, provides the necessary information and procedures to provide effective training about pesticide safety topics. A course fee of $35 covers the cost of the hosting, course maintenance, and certification management.

Iowa State University is working with PERC to transition to the new course. The ISU WPS Train-the-Trainer online course will no longer be available after October 15, 2018. Anyone who has previously completed the ISU online course does not need to complete the new PERC course unless they want to be qualified to train pesticide handlers in addition to workers. 

Category: Pesticide EducationTags: Worker Protection StandardAuthor: Elizabeth Buffington

Insights into 2018 Corn Dry Down

Fri, 09/21/2018 - 09:57

Corn and soybean harvest has started across many parts of Iowa. Some areas of the state have swung between warm-dry and cool- wet weather within the last few days. With more rain in the forecast, a few producers may be wondering about how fast corn will dry down in the field in the coming weeks. Last fall we wrote an ICM News article highlighting the factors associated with corn grain dry down. In a nutshell: after the crop has reached maturity, the rate of grain dry down is largely driven by air temperature and relative humidity.

Corn grain dry down is typically not a concern during a warm, dry fall. Grain moisture often reaches near 15% by mid-October. However, with cool, wet weather it may take until early to mid-November to reach 15%.

Simulated dry down of hypothetical mid-September maturing crops during two contrasting weather years 1999 (warm-dry) and 2009 (cool-wet).


Measurements from our field experiments in Ames, Iowa show corn grain moisture to be between 23 and 30% as of September 20th. Assuming 34% grain moisture at black layer, early-September maturing corn should be getting close to 20% moisture, while mid-September maturing corn should be just below 29%. Our projections using historical weather data puts grain moisture in Ames between 18 and 22% by October 1 (Table 1 and Figure 2). Corn grain may not reach 15% moisture until the second week of October. In order to avoid harvest delays, we recommend making plans to dry corn post-harvest, especially if weather shifts back to cool and wet.

Anticipated corn grain moisture dry down for Ames Iowa.


Cooler, wetter weather conditions not only have implications on grain moisture but also grain quality. It should be expected that ear molds will increase and may lead to mycotoxins. Because of this, it is recommended that farmers scout fields and prioritize for early harvest those at highest risk of ear mold proliferation. This is extremely important for late planted, late maturing crops where attaining grain moisture near 15% in the field will become less likely as we move into late October and early November.

Category: Crop ProductionTags: Corncorn harvestdrydownAuthors: Rafael Martinez-FeriaSotirios ArchontoulisMark LichtCrop(s): Corn

Samples of Tar Spot in Corn Needed for Research

Wed, 09/12/2018 - 10:54

The University of Illinois, Urbana, is seeking assistance from its friendly neighbor to the west, the corn-state of Iowa, in locating samples of tar spot in corn. This is part of the university’s new research project investigating the genetic variability of the tar spot pathogen.

Tar spot symptoms are small, black raised spots — that can be circular or oval — and may appear on one or both sides of leaves, leaf sheaths and husks. These spots can be found on both healthy green leaves and dying (brown) tissue. The black spots are surrounded by a tan or brown halo, which can be especially obvious on healthy leaves.

Tar spot of corn is a new corn disease first identified in the U.S. in 2015 in Illinois and Indiana. It has since been confirmed in Iowa, Michigan, Wisconsin and Florida. Researchers haven’t seen data that tar spot in corn directly causes yield loss, however, in research conducted in Mexico and South America, the fungus Monographella maydis follows the tar spot fungus and does cause yield loss.

If you have, or believe that you have a sample of corn tar spot, the University of Illinois would be greatly appreciative of your assistance in helping them with their project. If interested, please collect several leaves showing the symptoms and send them in using this form. Please wrap the leaves in newspaper or dry paper towels and ship in a large envelope. Please ship the samples early in the week. If sending samples from multiple locations, please label them and provide the appropriate information to the form.

Here is an additional permit that will allow the university to receive out of state samples, that should be included in the sample package.

Should you have any question, please contact Diane Plewa, of the University of Illinois Plant Clinic.

“If anyone in the state has any samples of tar spot, it would be great if they could assist the University of Illinois in their research,” said Extension Plant Pathologist and Director of the Iowa State University Integrated Pest Management (IPM) program Daren Mueller. “University collaboration is important to the overall mission of IPM, as it allows us to find better, more efficient solutions to control pests. With tar spot in corn having a presence in Iowa, this research could play a critical role in helping us to be prepared in the event that the pathogen becomes a dominant factor in crop production.”

Category: Plant DiseasesTags: tar spotIPMfungusCornAuthors: Ethan StoetzerDaren MuellerCrop(s): Corn

2018 Labor Day Palmer amaranth tour

Mon, 09/03/2018 - 08:53

It's Labor Day weekend, that means it's time for me to see what's happening at the first three Palmer amaranth infestations in western Iowa. The infestations (Harrison, Fremont, and Page Counties) were first reported in 2013.  Harrison County had two fields (approximately 50 acres) with extensive populations, whereas the other two involved scattered plants located primarily outside of production fields.

In Harrison county it was encouraging to see continuous declines in the number of Palmer amaranth escapes.  I didn't find any plants during a brief jaunt into the corn field.  In previous years an area filled with abandoned equipment had always contained a significant Palmer amaranth infestation. This area had been cleaned out and reseeded to perennial grass (Figure 1).  While there were a few, late-season escapes producing seed, in future years the established sod should prevent future Palmer escapes.  There were also a few Palmer amaranth along the road edge, but fewer than in past years.  Stop one on this year's tour was encouraging, now it was time to follow the loess hills south to Fremont county (Figure 2) and determine the state of Palmer amaranth in the southwest corner of Iowa.

Unfortunately, the news in the southwest corner of the state was not as encouraging as in Harrison County.  Initially I was happy to see a ditch that had been filled with Palmer in 2017 was now dominated by kochia and waterhemp.  I suspect this shift was due to natural succession rather than any practices implemented by the county or landowners.  The original infestation in Fremont County was found in a seed company's show plots, and the company has taken efforts (hand roguing and spraying) the past two years to eliminate these plants.  There were a few escapes outside of the plots, but far fewer than in earlier years (Figure 3). Things went downhill quickly after those two observations.  A sweet corn patch across the road has been a playground for Palmer the previous three years, and 2018 was no different (Figure 4).  It is disheartening to think how many millions of seed are being produced in this half acre plot, and where those seeds will move to.  While pondering this, the county sheriff stopped by to inquire if I was lost.  While explaining what I was up to, it was clear he was wondering what kind of person doesn't have anything better to do on a three day weekend than drive around western Iowa looking for weeds.  

The final stop was in Page County. At this location the Palmer is located on the grounds of an ag retailer and in an adjacent field.  Because of wet conditions, I didn't venture into the corn; but the waterways in the field that harbored Palmer in previous years were clean.  There have always been a few escapes around the grounds of the retailer, but it was obvious the company had made efforts to manage the population. This year those efforts weren't apparent, and there were more and larger plants scattered across the grounds than I had observed before.

In summary, if I were to rate the management efforts at the three sites, I would give a thumbs up to Harrison County, and thumbs down to the other two. Early detection and eradication should be the objective for managing new infestations of weeds. It is encouraging to see improvements in management at the Harrison County site where eradication will be most difficult due to the size of this infestation at detection.  Eradication should be  easier at the other sites because of their limited size, but efforts there appear to be lacking.  I hope that in 20 years we don't look back and say "sure wish we would have gone after the Palmer when it was first found".

Previous summaries
2017 Tour
2016 Tour
2015 Tour

Figure 1.  Palmer escape in newly seeded area at Harrison County site.

Figure 2.  Loess hills overlook from Waubonsie State Park in Fremont County. I didn't spot any Palmer in the valley below.


Figure 3.  Palmer escapes outside of show plots in Fremont County.

Figure 4.  Palmer amaranth fulfilling its potential in Fremont County.


Category: WeedsTags: palmer amaranthAuthor: Bob Hartzler