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High yields despite drought conditions

Fri, 01/05/2018 - 09:50

Most of Iowa was wet and cool during planting time (end April to mid-May), warm and dry during vegetative growth (June to July), and cool and wet during reproductive development (August to September). In some locations, the June-July drought was severe with precipitation deficits exceeding eight inches. Despite this drought, yields were high and above the long-term trend for a third straight year.

In-season rainfall is not the only source of water for crops in Iowa. Stored soil water and shallow groundwater were significant contributors to total water uptake. For this reason, crops survived the June-July drought. Field measurements revealed that the depth to water table was approximately five to six feet below the soil surface in mid-July (corn silking time) and crop roots had reached that depth. Deep roots and shallow water tables compensated for much of the precipitation deficit. In fact, below normal June precipitation is favorable in Iowa for two reasons: i) rapid and unconstrained root growth (up to 1.3 inches per day); ii) given generally high soil water content in the early spring, additional precipitation will stimulate nitrogen loss.

In terms of grain yield equivalent, model analyses suggest that root access to shallow groundwater accounted for 1% to 46% of total grain yield. The contribution was lower in sites with sufficient rain and higher in sites with drought. In addition to water, the same analyses indicated that the subsoil had more than enough nutrients for sustaining high crop yields.

Cool temperatures in August and September reduced transpiration rates, slowed development, and extended the grain-filling period. Additionally, the growing season was extended by a later than normal first killing frost in the fall. This resulted in higher than normal seed weight in corn.

Together, these factors contributed to surprisingly high corn yields in 2017. Quantifying temperature, precipitation, and water table dynamics across the state has been an important component of moving the science of digital agriculture forward to enable better predictions of yield and will greatly assist management decisions and predictability of crop yields and nitrogen losses.

Figure 1: Cumulative difference between 2017 precipitation and 35-yr average for five locations in Iowa. SW = southwest, NE = Northeast, NW = Northwest, SE = Southeast. Grain yields ranged from 190 to 235 bu/ac. 

Figure 2: Cumulative difference between 2017 cummulative GDD and 35-yr average for five locations in Iowa. SW = southwest, NE = Northeast, NW = Northwest, SE = Southeast. Grain yields ranged from 190 to 235 bu/ac. 

Figure 3. Leaf number, node number, and grain yield (top panels) and water table and root depth (bottom panels) for corn in central Iowa (left panels) and soybean in southeast Iowa (right panels) in 2016. Ordonez et al., 2018.

Category: Crop ProductionTags: groundwaterrootsWeatherdroughtyieldAuthors: Sotirios ArchontoulisMark LichtMike CastellanoCrop(s): CornSoybean

Dicamba: Past, Present, and Future

Wed, 12/27/2017 - 15:37

Dicamba has been an important component of Iowa weed management systems for more than 40 years.  The history of its use is somewhat unique in that its popularity has ebbed and flowed over time.  The increase in herbicide resistant weeds combined with the introduction of dicamba-resistant soybean (Xtend) promises a large increase in dicamba use in both corn and soybean.  This article will review the characteristics of dicamba that differentiate it from other herbicides, provide an overview of problems observed in 2017, and describe how risks can be minimized in 2018.


The discovery of 2,4-D and other phenoxy herbicides in the 1940’s started the era of chemical weed management.  Dicamba was first described in 1958, and registered for use in 1962.  These herbicides mimic the action of auxin (indoleacetic acid), and are frequently referred to as growth regulator herbicides, synthetic auxins, or Group 4 herbicides (Table 1).  They bind to the receptor for auxin and initiate transcription of genes involved in cell growth.  While plants can closely regulate concentrations of auxin within cells, they lack this ability with the Group 4 herbicides.   Presence of Group 4 herbicides in cells results in deregulation of numerous important processes, resulting in abnormal growth and/or plant death.  

Table 1.  Chemical families that interfere with auxin activity (Group 4 Herbicides).

Chemical family Active ingredient Tradename Phenoxy 2,4-D Weedone, many others   2,4-DB Butyrac   MCPA Mecocrop       Benzoic acids dicamba Banvel, Clarity, Engenia, Xtendimax
with Vapor Grip Technology, many others   chloramben Amiben       Carboxylic acids, Pyridines triclopyr Garlon, Remedy Ultra   clopyralid Stinger, Transline   aminopyralid Milestone   picloram Tordon   aminocyclopyrachlor Streamline

Herbicide activity

Nearly all Group 4 herbicides selectively control broadleaves in grass crops.  The exception is quinclorac which is used to control certain weedy grasses in rice and turf.  There is a wide range in selectivity among the products, and they are commonly used in combination to provide a broader spectrum of weed control.   A combination of 2,4-D and dicamba was the most popular postemergence program in Iowa corn production in the 1970’s and early 1980’s.  Dicamba was more active on smartweed than 2,4-D, whereas 2,4-D provided better control of velvetleaf.

Group 4 herbicides vary widely in soil persistence, and hence, length of residual weed control.   Generally, the phenoxy herbicides have the shortest half-lives of the Group 4 herbicides, whereas the pyridines are most persistent.  An advantage of dicamba over 2,4-D for use in resistant soybean is dicamba’s longer half-life (14 days) compared to 2,4-D (6 days); however, the half-life of dicamba is less than half of most preemergence herbicides.  Thus, the value of dicamba as a preemergence herbicide is limited for managing  weeds with prolonged emergence patterns, such as waterhemp.

Plant sensitivity
Group 4 herbicides induce plant responses at lower fractions of use rates than most other herbicides.  For example, it takes 1% of the standard glyphosate use rate (0.75 lb/A) to injure corn, whereas 0.005% of the dicamba use rate (0.5 lb/A) can injure soybean (Figure 1).  Due to this high activity, injury to sensitive plants outside of treated areas has been a problem since the introduction of Group 4 herbicides.  In a 1971 bulletin, Dr. Ellery Knake, extension weed scientist at the University of Illinois, discouraged the use of dicamba in Illinois due to the sensitivity of soybean to the herbicide.   Improvements in application technology have reduced, but not eliminated, problems with off-target movement of the Group 4 herbicides.

Figure 1.  Fraction of labeled rate required to cause visible injury on susceptible species.  Adapted from Bhatti et al. (1996), Everitt and Keeling (2009) and Solomon and Bradley (2014).

Another distinguishing characteristic of dicamba and certain other Group 4 products is their relatively high vapor pressure.  Herbicides with high vapor pressures may evaporate following application, resulting in off-target movement even when the applicator uses appropriate application practices.  The combination of vapor loss and the high sensitivity of certain plant species to dicamba results in a higher risk of off-target injury than with most other herbicides.  The following factors influence the potential for dicamba volatilization following application.

Temperature.  The potential for dicamba to volatilize increases as temperature increases.  A threshold of 85° F is frequently cited as the temperature where caution should be used when applying dicamba in the vicinity of sensitive vegetation.  Minnesota and North Dakota recently prohibited applications of dicamba if air temperature is forecast to exceed 85° F the day of application due to increasing risk of volatility.

Application surface.  The amount of dicamba that volatilizes varies depending on the characteristic of the surface it lands upon.  Behrens and Leuschen (1979) reported that approximately 35% more dicamba volatilized off corn and soybean leaves than from a silt loam soil.  Thus, there is greater risk of volatilization with postemergence applications when significant herbicide is intercepted by the crop rather than the soil surface. 

Formulation.  Almost all postemergence herbicides are weak acids, compounds capable of donating a proton (hydrogen ion).  These herbicides are often formulated as a salt of the parent acid, replacing the hydrogen with some other positively charged ion (e.g. dimethylamine, potassium, etc.).  There are a variety of reasons why salts of the parent acid are used rather than the acid itself, but improving compatibility with hard water and tank-mix products is a primary reason. The volatility of dicamba and certain other herbicides is also influenced by formulation. 

Several formulations of dicamba have been introduced with the intention of reducing the risk of volatilization.  The parent acid of dicamba is the form of the molecule that volatilizes following application.  Low-volatile formulations such as Clarity, Engenia, and Xtendimax with Vapor Grip Technology are intended to reduce the amount of dicamba disassociating to the parent acid. Independent research has verified these formulations reduce volatilization compared to the original dimethylamine salt used in Banvel, but they do not eliminate these losses.

The 2017 Iowa experience

In December the Iowa Department of Agriculture and Land Stewardship (IDALS) reported there were 253 pesticide misuse complaints in 2017, a record number. This increase was largely due to 157 off-target injury complaints associated with growth regulator herbicides, the majority involving dicamba.  It is important to recognize the number of formal complaints to IDALS is a small fraction of total problems associated with pesticide applications. At the time this article was written IDALS had not released the breakdown on the percentage of complaints associated with contaminated spray equipment, particle drift, and volatilization. Most people involved in investigating dicamba complaints acknowledge that multiple avenues of dicamba exposure were involved with off-target injury.  Problems associated with contaminated spray equipment and particle drift can be minimized through better training and improved decision making; however, risks associated with volatilization are not easily managed since vapor movement is determined by the environment following application rather than actions of the applicator.

Moving forward in 2018

There has been considerable debate on how to reduce off-target movement associated with dicamba use in soybean. The United States Environmental Protection Agency (EPA) introduced several important label changes for the new products registered for use on dicamba-resistant soybean. These products are now classified as Restricted Use Products (RUPs).  This classification requires users of the products to be certified applicators, and also requires recordkeeping above-and-beyond those necessary for other RUPs.  In addition, applicators of the products will be required to complete dicamba-specific training prior to use.  The maximum wind speed allowed for applications was reduced from 15 MPH to 10 MPH, and applications are limited to hours between sunrise and sunset.  Label language regarding sprayer cleanout and avoiding applications near susceptible crops has been expanded.  These label changes are appropriate, and should reduce problems associated with particle drift and sprayer contamination.  However, they do not address the issue of off-target movement associated with dicamba volatilization. 

Due to concerns regarding volatilization of dicamba, ISU Weed Science recommends that dicamba only be used preplant or preemergence in dicamba-resistant soybean. Preemergence applications of dicamba reduce the value of dicamba in managing waterhemp, but in our opinion, the risks associated with postemergence applications exceed the weed management benefits.  While early postemergence applications made in May would reduce the volatility risk compared to June applications, label restrictions regarding wind and rain would frequently delay applications into high-risk scenarios (i.e. temperatures above 85° F, nearby soybean reaching sensitive stages).

In summary, dicamba has been a popular herbicide in Iowa corn production for nearly 40 years.  Farmers have learned how to manage dicamba in corn while minimizing risks associated with off-target injury.  Postemergence use in dicamba-resistant soybean presents a much greater challenge due to higher temperatures and more advanced development of adjacent sensitive crops, particularly soybean.   Failure to significantly reduce complaints associated with off-target injury may result in further restrictions on not only dicamba products, but also on other pesticides used in crop production.

Behrens, R. and W. E. Lueschen. 1979. Dicamba volatility. Weed Sci. 27:486-493.

Bhatti, M.A. et al.  1996.  Wine grape response to repeated exposure of selected sulfonylurea herbicides and 2,4-D.  Weed Technol. 10:951-956.

Ellis, J.M. et al.  2003.  Rice and corn response to simulated drift of glyphosate and glufosinate.  Weed Technol. 17:452-460.

Everitt, J.D. and J.W. Keeling.  2009.  Cotton growth and yield response to simulated 2,4-D and dicamba drift.  Weed Technol. 23:503-506.

Solomon, C.B. and K.W. Bradley.  2014.  Influence of application timings and sublethal rates of synthetic auxin herbicides on soybean.  Weed Technol. 454-464.

Category: WeedsTags: dicambaXtend soybeandicamba resistant soybeanAuthor: Bob Hartzler

A historical perspective on dicamba

Tue, 12/19/2017 - 08:30

At the recent North Central Weed Science Society annual meeting I was asked to provide the opening presentation (A historical perspective on dicamba) in a symposium focusing on issues with dicamba.  Following are the slides and the abstract of my presentation.

Powerpoint presentation pdf

The auxin-like activity of the phenoxyacetic and benzoic acids was discovered in the early-1940’s. The herbicide dicamba was first described in 1958, Velsicol acquired the patent for the molecule, and dicamba was first approved for use in the US in 1962. In subsequent years, the label was expanded for use on a wide range of grass crops and for non-crop areas. Dicamba has been described as either a benzoic acid or carboxylic acid compound, and mimics the activity of indole-3-acetic acid (Group 4 herbicide). According to USDA/ERS data, dicamba was used on less than 10% of US corn acres in 1979. Use increased to 15% of corn hectares by 1990, then as herbicide-resistant weeds spread, dicamba use on corn increased to 28% of hectares in 1995. Prior to the introduction of herbicide-resistant crops and Group 27 herbicides (HPPD inhibitors), dicamba primarily competed with atrazine and 2,4-D for broadleaf weed control in corn. Atrazine was preferred over dicamba and 2,4-D by most farmers due to its preemergence use, greater margin of crop safety, and lower risk of off-target injury. Dicamba use was much higher in northern states with high pH soils due to the carryover risk associated with atrazine. Dicamba was used on more that 70% of the 1985 corn hectares in North-Central and Northwest Iowa, compared to 12% of US corn hectares. High pH soils in this region prevented use of atrazine rates greater than 1 kg ha-1 when rotating to soybean or other sensitive crops. The high sensitivity of soybean to dicamba has been an issue since its introduction. In a 1971 University of Illinois Extension bulletin, Dr. Ellery Knake discouraged the use of dicamba due to the risk it posed to adjacent soybean. Behrens and Leuschen published a seminal paper in 1979 reporting on factors that influence volatility of dicamba, including temperature, rainfall following application, application surface (soil vs foliar interception), and formulation. A wide range in volatility was found among the salts of dicamba evaluated. The first dicamba product (Banvel) contained the dimethylamine salt of the parent acid. Over the years, several different salts of dicamba have been introduced, often with the intent of reducing dicamba volatility. Low volatility formulations include Banvel II (sodium) in 1981, Clarity (diglycolamine) in 1990, and most recently Xtendimax/Fexapan with Vaporgrip Technology (diglycolamine) and Engenia (BAPMA). Current research will determine the reductions in volatility achieved with these formulations. Increasing problems with herbicide-resistant weeds have led to an increase in dicamba use, and the introduction of dicamba-tolerant crops will continue this trend. The International Survey of Herbicide Resistant Weeds lists 36 weed species with evolved resistance to Group 4 herbicides, seven of these species are reported to be resistant to dicamba.

Category: WeedsTags: dicambaAuthor: Bob Hartzler

Soil Fertility Web Site Update

Mon, 12/18/2017 - 08:06

The Iowa State University Extension and Outreach Soil Fertility web site has undergone a recent redesign and update. The site was updated, but the URL has remained the same (http://www.agronext.iastate.edu/soilfertility/). While the site has been a resource for several years, it was in need of an overhaul. Part of the update was to improve flow and access to the different areas of the site. Other updates were needed to meet university requirements.

The original Nutrient Topics areas are still there, such as lime and soil pH, nitrogen, phosphorus, potassium, manure nutrients, secondary and micronutrients, soil/plant sampling and testing, and nutrients and water quality. In each nutrient topic section, information is available that is pertinent to that topic; including Extension and Outreach publications, newsletter articles, conference proceedings and reports, presentations, and links to related web sites. The Photo Gallery still contains a large number of nutrient related pictures. As before, the Current Topic articles are still located on the main page. New features include a Quick Links list and a featured web site or publication on each page.

We hope you will use the ISU Agronomy Extension Soil Fertility Web Site as your source of soil fertility information and your initial stop when accessing the Web.

Category: Soil FertilityTags: soil fertility websiteAuthors: John SawyerAntonio MallarinoCrop(s): CornSoybeanBiomass and ForageCover Crop

What’s the real deal with soybean cyst nematodes and cover crops?

Wed, 11/29/2017 - 13:43

The number of acres planted to cover crops annually has been steadily increasing in recent years throughout the United States. Meanwhile, the soybean cyst nematode (SCN) continues to sit atop of the U.S. list of yield-suppressing pathogens. It’s no coincidence, then, that there is an increasing interest regarding the potential for these two factors to interact in the field, particularly with the possibility that cover crops could decrease SCN population densities (numbers).

When considering the potential effects of cover crops on SCN, there are several possibilities. First, it is possible that cover crops could serve as hosts for SCN reproduction, thereby inadvertently increasing SCN population densities in fields where these plants are grown. Many cover crop species have been found to be non-hosts for SCN; however, we cannot say that all cover crops are non-hosts as some species can support SCN reproduction, including crimson clover, field pennycress, and more. Second, it is possible that there is no effect of cover crops on SCN population densities. Lastly, and most interestingly, there is the potential that cover crops may decrease SCN population densities. 

There are several mechanisms through which cover crops could decrease SCN population densities - as explained in the table below.

Mechanism Details Producing nematicidal compounds Some plants, notably members of the Brassicaceae family (which includes radish, mustard, and canola), produce methyl-isothiocyanates as they decompose. These compounds have nematicidal properties. Serving as a
trap crop If SCN juveniles hatch and enter roots of cover crops, it is unlikely they will be able to serve as a host. Being unable to establish a feeding cell, the juveniles would subsequently be “trapped” and die in the plant roots. Ideally, to serve as an effective trap crop, many nematodes would enter the roots to decrease SCN numbers. Inducing hatching of juveniles from eggs As plants grow, the roots in the soil give off compounds called root exudates. It is possible that cover crop root exudates could stimulate hatch of SCN juveniles in the fall or spring. If the juveniles hatch at these times, there is likely no food source for them so they would die of starvation in the soil. Producing inhibitory allelochemicals Some plant roots may produce inhibitory allelochemicals, either while living or decomposing, that affect other organisms. Such allelochemicals may inhibit the hatch of SCN juveniles, which would make the pathogen less productive overall. 

There have been few published scientific studies of how different cover crop species may have a negative effect on SCN numbers. Additionally, there are no data on whether different cultivars within a species of cover crop have differential impacts on SCN numbers.

Some companies describe cover crops as providing benefits such as “reducing SCN population densities” or more generally as “decreasing nematode populations” but there are no data to substantiate the claims. There are a few scientific reports that suggest some cover crop species can reduce SCN population densities. These reports lack necessary details of the studies, were not reproduced over a sufficient range of locations and growing seasons, and/or contain results that are inconsistent among locations and years.

The situation described above leads to the premise of the cover crop and SCN experiments that I am working on in Greg Tylka's lab at Iowa State University, funded in part by NCR-SARE's Graduate Student Grant Program. While we have an inkling of an idea about how cover crops could affect SCN population densities, my work is taking a deep dive into this interaction to provide a well-thought-out and comprehensive look at this interaction. The experiments I am conducting range from very large scale, on-farm strip trials coordinated though a collaborative effort with the Iowa Soybean Association, to laboratory assessments of how root exudates from specific cover crops may affect the hatch of SCN juveniles.

Cover crops growing in late fall in an SCN-soybean research experiment at the ISU Northern Research and Demonstration Farm in Kanawha, Iowa.

The potential benefit of cover crops in decreasing SCN population densities and the scarcity of robust data describing the situation are why I am working to determine the effects of cover crops on SCN at Iowa State University. Researchers at other universities in the North Central region are working on this puzzle as well, including those at Michigan State University, University of Missouri, North Dakota State University, Ohio State University, and perhaps even other institutions. With these combined efforts, there should be a much clearer understanding of the potential benefits and limitations of cover crops for managing SCN in the upcoming years.

Category: Plant DiseasesTags: cover cropsSCN managementSCNAuthor: Chelsea HarbachCrop(s): Soybean

Addressing the Edge or Border Effect on Corn Yields

Mon, 11/06/2017 - 09:03

There have been many reports of corn along the edge of the fields yielding drastically less than the remainder of the field. In many cases, the yield loss is most obvious on the southern edge of the field, but it has been observed along the west, east, and north sides of fields this year. This has left many growers wondering what caused this. Some hypothesized causes are herbicide drift or an edge effect from the hot, dry winds and stressful conditions this summer.

In most cases the corn plants reportedly appeared to be normal. Some noted plants were slightly shorter along the edges, but the plants were not considerably stunted. Others observations include shorter ears or barren plants. While no specific data appears to exist on this phenomenon, let’s discuss what might have happened.


It was dryer and warmer than normal in the northwest and southeast areas of the state during the critical stages of corn ear development this year. A moderate drought began to develop late in June and became progressively worse, encompassing much of Iowa by late July. It is during this period that corn ears develop and set seed. While modern corn hybrids have been selected for better stress and drought tolerance, ear and kernel development is still vulnerable when drought occurs in June and July. Ear growth may be stunted even if the rest of the plant appears to be growing normally. Slightly shorter plants with barren ears are common symptoms of a progressively severe drought during ear development, like the one present in Iowa this summer.

These images illustrate the progression of the drought that occurred during the 2017 growing season. Source: U.S. Drought Monitor. 

Microclimate effects

A corn crop with plenty of water will be several degrees cooler than the surrounding air during the day.  This is because the water moving from the soil through the plant into the atmosphere takes energy with it as it evaporates from the leaves. This process (called transpiration) is very important for a canopy of plants because it keeps them cool on hot days, allows them to accumulate biomass rapidly (through photosynthesis), and helps them extract nutrients from the soil. The plants at the edge of the field, however, are at a disadvantage relative to those further in the field. Their local microclimate is affected more by the atmospheric conditions outside the field. 

In Iowa, the common belief is that winds generally come from a southerly direction. Under drought conditions, these winds often are warmer and dryer than the air within the canopy. As a consequence, the plants at the south side of the field will use water faster than those further in the canopy. The intensity of this microclimate effect would likely be greatest on the south edge of the field, followed by the west side with the afternoon sun and common southwest winds, followed by the east side with morning sun, followed by the north side which is best protected.  The impact of the ‘edge effect’ on yield is determined by the initial soil moisture available to the plants and the timing/intensity of the developing drought conditions. Plants along the edge of the field showing signs of leaf rolling late in June/early July are a good indication the local microclimate is negatively impacting ear development.

While it may be the general belief that winds in Iowa generally come from a southerly direction, that may not always be the case, which is illustrated in wind rose plots below. A wind rose plot provides the frequencies of wind speed and direction. The length of each “spoke” around the circle is related to the frequency of time that the wind blows from that direction.

Looking at the wind rose for Ames, from June 1 to July 1, 2017, the winds from the south or southwest were the strongest and most predominant. However when looking at the wind rose for June 1 to July 31, 2017 the direction seems to be more variable.

Wind rose plots for Ames, IA for June 1 to July 1, 2017 (left) and June 1 to July 31, 2017 (right). Source: ISU Environmental Mesonet - https://mesonet.agron.iastate.edu/sites/windrose.phtml?station=AMW&network=IA_ASOS.  

Herbicide drift
Some have been quick to blame herbicide drift from neighboring soybean fields. It is impossible to diagnose crop injury from herbicide drift after the crops have been harvested.  As problems with herbicide-resistant waterhemp have increased, more soybean fields are treated with ‘rescue’ treatments applied relatively late in the season. Corn in adjacent crop fields may be in reproductive stages, and not display injury symptoms associated with herbicide exposure during vegetative growth.  Little information is available on herbicide exposure to corn at these stages, but research with fungicide applications during corn reproductive stages illustrate how unexpected responses can occur. There is no research indicating herbicide drift could cause the edge effect yield loss, but the possibility cannot be ruled out either. The only way to assess whether herbicide damage might have been involved is to walk the fields after herbicides are applied. 

While we cannot pinpoint exactly what caused the lower yields along the edges of some fields and perhaps it is a combination of different factors, this phenomena is not going unnoticed and serves as a good reminder to scout fields during the growing season. Spend time scouting around the during the ear initiation period (V5 to V6) to see if there are stresses that might affect ear development. Also, check fields shortly after nearby fields have had a post emergence application for potential herbicide drift issues. 

Article written by: 

Dr. Mark Westgate, Professor, Crop Production and Physiology ISU Agronomy Department 

Rebecca Vittetoe, ISU Extension and Outreach Field Agronomist 

Category: Crop ProductionTags: edge effectCornyieldsAuthor: Rebecca VittetoeCrop(s): Corn

Now is the Time for Farmers to Turn on Fans

Thu, 10/26/2017 - 15:40

Up to this point in the harvest season we have been short on grain dry down and cooling weather. Corn moisture percentages have been hanging in the 20’s, sometimes in the upper 20’s. This past week eliminated much of the moisture, but favorable field dry down weather rarely continues into November. Farmers should now focus their attention on cooling, both of wet corn in holding or air dry situations, and of dried corn being removed from dryers. Inadequate or delayed cooling is very costly to future storage properties. Remember, a significant portion of the 2017 crop will be held over for more than one year, as carryovers expand.

Starting Friday morning, great conditions arise to get grain cooled down from this Fall’s harvest. With the average daily temperatures predicted to be in the mid- 30s to low- 40s for Friday well into next week, this will be a perfect time to get recently harvested corn and soybeans cooled to a temperature required for winter storage. Allowable storage time for grain roughly doubles for every 10 degree drop in temperature. So, getting grain cooled down soon after harvest will significantly improve chances of keeping it in good condition while in storage.

In order to determine the length of time it will take to cool a bin of grain, first determine how much fan horsepower you have per 1,000 bushels. For example, if you have a 5 hp fan on a 20,000-bushel bin, you have 0.25 hp/1,000 bu. Divide this number into 15 and you get an estimate of the hours it will take to cool the full bin.  In this example, 15 / 0.25 = 60 hours.

Air dew point is a rough measure of how low grain temperature can be reduced. For example, right now the temperature is 63°F and the dew point is 44°F. A 20- degree difference is good; the larger the difference, the greater chance that air will dry corn, and 44°F is approaching the below 40°F temperatures required for storage.

There will be a lot of long term storage this year, so cool rapidly now to prevent mold and insect damage next Spring and Summer.

Category: Grain Handling and StorageTags: grain dryingcorn storagecooling temperatureCornAuthors: Greg BrennemanCharles R HurburghCrop(s): Corn

Sampling for Nematodes on Corn in the Fall is Not Advised

Mon, 10/23/2017 - 16:07

I’ve received lots of inquiries in the past few weeks about sampling fields for nematodes that feed on corn. Most every Iowa field has one or more different nematode species present at low numbers. But it’s only when numbers are at damaging levels that yield loss will occur.

Unfortunately, there is no reliable relationship between the numbers of nematodes that feed on corn in soil samples collected in the fall and the damage that the nematodes may (or may not) have caused earlier in the growing season. Also, numbers of nematodes in fall samples do not correlate or predict the potential for damage in the next growing season.

Sampling to check for damaging levels of nematodes on corn needs to be done during the growing season - ideally when symptoms of damage are seen.

Look for an ICM News article on this topic for more information about how to take samples in-season to assess the situation with nematodes that can feed on corn.

Category: Plant DiseasesTags: nematodesnematode damage to cornAuthor: Greg TylkaCrop(s): Corn

The Quincy, M.E. Field Calls of Harvest 2017

Fri, 10/20/2017 - 10:07

I grew up watching the television show Quincy, M.E.  Jack Klugman starred as a Los Angeles County medical examiner in the mystery-thriller, one-hour show as Quincy who had to solve mysterious deaths.  I would argue this show set the tone for future shows such as CSI: Crime Scene Investigation and NCIS.  These shows lead us to believe we can easily solve crimes and determine the cause of death. 

How does this relate to harvest 2017?  My extension colleagues and I often joke that we get Quincy M.E. calls during harvest every year. The body is dead (crop maturity) and now the client wants to know what caused the death or in this case the unexpected loss of yield.  The crop is harvested, the yield is not as good as the client had anticipated, or the yield varies widely from one end of the field to the other and now the client wants to know why.  Farmers often leave us a check strip of the affected “body”, but the “body” or crop is so far gone, it is difficult to always ascertain what might have limited yield. 

Was it the dry conditions of the growing season? If so, why was yield so variable across the field.  Did the crop experience off-target movement of a herbicide that may have caused yield loss? Well, it may have, but there is no good way to identify that cause in October.  Even knowing that some herbicides cause specific ear conditions in corn, other factors can cause similar conditions in corn. Was it compaction? Well, maybe we can tell when we dig roots and see limited root growth, or perhaps we note tomahawk roots indicating sidewall compaction during planting.  Was it rootworm damage? Perhaps. At this stage, it may be difficult to distinguish some rootworm feeding from normal root degradation. Was it a foliar disease? Hard to tell now when all the leaves are brown on the corn, or completely dropped in the soybeans.  Sometimes we can still see patterns in the field, even with mature crops, that might provide some clue as to what happened, but this clue is harder to recognize with dropped leaves or collapsing corn stalks. 

Extension field agronomists and retail agronomists are asked to solve many “murder mysteries” in production crop fields. This is part of the job.  However, sometimes agronomists need to be able to see the clues when the clues are fresh.  For example, identifying the impact of a foliar disease requires seeing the crop much earlier in the season to determine the actual disease and the severity. Sometimes the “body” dies of natural causes, sometimes the “body” dies from complex plant-soil-climate interactions. Sometimes the “body” is murdered from complications of unintended consequences such planting in wet soils, herbicide drift, weather or other reasons.  And sometimes those unintended consequences are aided and abetted by mother nature with too much rain, not enough rain, too much heat, not enough heat. 

Take some time to review the growing season conditions to determine what may have impacted that crop. Feel free to call your extension field agronomist yet this fall, but recognize that the clues may be long gone and the mystery may go unsolved. Most importantly, plan now for several scouting trips for 2018, keep good notes and do visual observations throughout the growing season.  Feel free to call your extension field agronomist when you are uncertain about the cause of what you are seeing during the growing season.


Category: Crop ProductionTags: growing seasoncrop maturityfield callsAuthor: Angie Rieck-HinzCrop(s): CornSoybean

Fall armyworm feeding noted in cover crop fields in SE/SC Iowa

Mon, 10/16/2017 - 15:59

Fall is usually not a time I expect to get questions about armyworm infestations, but last week I received several questions about fall armyworms in cover crop fields, particularly in cereal rye, triticale, or wheat cover crop fields. In Iowa, fall armyworms can be pests in corn, hayfields and pastures, but this is the first time that I’ve seen them as a pest in cover crop fields.

Fall armyworms are unpredictable pests that do not overwinter in Iowa. While the larvae vary in color, most fall armyworms are black in color. They have three narrow, yellowish white lines running down the back from the head to the end of their abdomen. They also have a wider dark strip and a wavy yellow-red blotched stripe on each side of the body. Their head is dark brown with a prominent inverted “Y”.

Fall armyworms are typically black in color and have three narrow, yellowish white lines running down the back from the head to the end of their abdomen. 

The adult moths migrate north from the Gulf Coast states. The adults will lay eggs. Those eggs hatch, the larvae feed, and then pupate below the soil surface. Usually in Iowa we only see one generation of fall armyworm per year. Seeing fall armyworms in your cover crop fields this fall is no indication of whether you could potentially have issues with armyworms next spring.

Fall armyworm larvae feed on tender green tissues. Windowpane feeding is the first injury sign you’ll notice. Young larvae feed on the underside of the leaf, but leave the clear upper epidermis intact. This may give the field a “frosted” appearance. As the larvae grow, feeding is usually confined to leaf margins, but larvae can strip plants entirely of leaf tissue.

Fall armyworm feeding on a cereal rye cover crop in Wapello County, Iowa. The cover crop was drilled in a field harvested for corn silage. 

What do you do if you have fall armyworms in your cover crop field? Do you need to spray? Will the stand come back? Those are all great questions.

Where you may consider spraying is if you are planning on grazing or harvesting the cover crop for forage either this fall or next spring. With spraying, it’s important to consider the size of the larvae. In the fields I’ve looked at, most larvae are at least an inch long or longer. Larvae typically reach a length of 1 ¼ to 1 ½ inches long. Once the larvae get much bigger than ¾ inch long it is harder to control them. Additionally, fall armyworms cannot survive freezing temperatures. The treatment threshold to spray is three armyworms per square foot. If you do spray, be sure to follow pre-harvest intervals listed in the insecticide label. 

The field had a pretty good armyworm population, but notice the green regrowth on the rye plants. As long as the armyworms are present, they will continue to feed on the regrowth. 

For cover crop fields with extensive damage and that have been literally chewed to the ground, the question becomes will the cover crop come back? The growing point of cereal grains would still be below the ground, especially if the field was drilled, as the growing point doesn’t move above the soil surface until it reaches the jointing stage, which occurs in the spring. This is good news because it means the plants will continue to grow. However, as long as armyworms are still present in the field they will continue to eat off the new growth. Stand loss may be affected by how much regrowth there is before winter dormancy is induced. 

This pictures illustrates the amount of feeding the fall armyworms did in one field.They literally ate the entire field.   

Category: Insects and MitesTags: armywormAuthor: Rebecca VittetoeCrop(s): Cover Crop

Soybean Diseases publication custom printing opportunity

Fri, 10/13/2017 - 09:53

A new version of the Iowa State University Extension and Outreach publication Soybean Diseases is nearing completion. This new version has been completely redone and includes updated disease information, many new images and disease cycle illustrations, and soybean growth and development/staging charts. Sample pages are shown below. 

We are giving agribusiness and others the opportunity to order custom copies with their logo during the initial print run.

Ordering custom copies has two benefits. First, it allows publications to be obtained at a reduced cost and second, the publication will be customized with the logo of the agribusiness, commodity group, or other entity that places an order. Logos will be placed on the back cover on the lower right.

Pre-ordered publications with a custom-placed logo are $3.00 per copy and a minimum of 250 copies must be ordered.

If you would like to pre-order, contact Adam Sisson via email (ajsisson@iastate.edu) with the following information by November 1, 2017:

  • Number of copies requested. Minimum 250 copies, please. 
  • high quality “.eps” logo to place on the back cover. Preferably in white or “reverse.” Company identifiers (logos or wordmarks) may be added, but not specific product identifiers. 
  • Name and address for shipping 

Please send ordering information and direct any questions to Adam Sisson at ajsisson@iastate.edu. Due to review and printing processes, delivery is expected by early 2018.

Category: Plant DiseasesTags: custom printSoybeandiseasespublicationscoutingcrop protectionAuthor: Adam SissonCrop(s): Soybean

Keep an eye open for stalk rots

Fri, 10/06/2017 - 08:44

Over the past couple of weeks we’ve been doing stalk rot assessments at several of the ISU Research Farms including the Southeast Research and Demonstration Farm, the McNay Research Farm, and the Ames Farm. While the plants seemed to be standing well, minus where the raccoons had fun in one of the trials, it was not uncommon to find stalk rots in the plants we sliced open to evaluate.

This is a good reminder that initial symptoms of stalk rots are not easily observed. Unfortunately we typically don’t notice stalk rots until either the exterior stalk tissue is affected or lodging or snapping has occurred.

We encourage you to get out and take some time to evaluate your fields for stalk rots. Check stalk firmness by pinching the lower internodes (“pinch test”). If the stalk crushes easily by hand then the integrity has been reduced by stalk rot and the risk of lodging goes up.

An alternative to the pinch test is the push test. With the push test, push the plant tops approximately 30 degrees from vertical. If the plant fails to snap back to vertical, the stalk has been compromised by stalk rot. Either method works fine.

With both tests randomly select a minimum of 100 plants in the field. We suggest while walking through the field, stop at five different spots and evaluate 20 plants. You want to get a good representation of the field.  If more than 10 percent of plants in a field exhibit stalk rot symptoms, that field should be one of the first or next fields harvested to reduce the potential for plant lodging and for yield loss.

The shiny black blotches on this stalk rind are very characteristic of Anthracnose stalk rot. Photo taken 9/22/17 at the Southeast Research and Demonstration Farm. 

Discoloration and a rotting pith caused by a stalk rot. Photo taken 9/22/17 at the Southeast Research and Demonstration Farm.   

Related article: Towards a Successful Harvest: Stalk Rots and Standability Issues

Category: Plant DiseasesTags: stalk rotsAuthors: Alison RobertsonRebecca VittetoeCrop(s): Corn

47th Annual North Central Extension-Industry Soil Fertility Conference

Wed, 10/04/2017 - 11:48

If you would like to learn more about current soil fertility issues and research being conducted at universities across the North Central region, then consider attending the 47th Annual North Central Extension-Industry Soil Fertility Conference to be held November 15-16, 2017, from 1:00 p.m. to noon, at the Holiday Inn Airport in Des Moines, Iowa.

The conference will include invited presentations from university and industry leaders, research reports from university soil fertility researchers, and posters outlining research by graduate students at universities across the North Central region (Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Nebraska, North Dakota, Ohio, Ontario, Pennsylvania, South Dakota, and Wisconsin).

The conference will be approved for CCA credits.

Early registration ends October 20.

For all information about the conference, including registration and hotel arrangements, go to:

https://conference.ipni.net/conference/ncsfc2017 or conference.ipni.net.


Category: Soil FertilityTags: Soil Fertility ConferenceCCA creditsAuthor: John SawyerCrop(s): CornSoybean

A spider surprise!

Fri, 09/29/2017 - 09:49

This week, my technician Greg VanNostrand found a black widow in our storage Quonset at the ISU Johnson Research Farm. The farm is just south of Ames in Story County. She is an adult female and had a pile of dead body fragments below her web. Needless to say, she was healthy and happy in the Quonset. But Greg likes spiders and decided to bring her back to my lab (thanks?). He has successfully kept black widows (and other spiders) by feeding them flies from colonies in the Insectary.

Why do we care about black widow spiders? The females are considered highly venomous, but human deaths are rare compared to the number of people envenomated. People bitten by a female black widow may have swelling, redness, muscle pain, nausea, headache, and cramping. The venom contains several toxins and in general sounds like a painful experience. The good news is they are predators, and eat insects and pretty much anything that gets caught in their web. There are a few species of black widow in the U.S. and they have a wide distribution in the southern states. It is possible for black widows to live in Iowa, but finding them here is more likely because they were accidentally introduced instead of established.

Adult, female black widow, Latrodectus mactans. Photo by wiki.

Adult, male black widow, Latrodectus mactans. Photo by Center for Invasive Species Research, University of California-Riverside.

It was hard to take a good picture of the male and female spiders through the plastic rearing chambers in my lab. I didn't feel brave enough to take the lids off and get a close-up.

Category: Insects and MitesTags: spiderblack widowAuthor: Erin Hodgson