Waterhemp control is an increasing challenge for soybean producers due to the evolution of multiple herbicide-resistant populations. With dwindling herbicide resources, there is a need to integrate non-chemical strategies into current weed management programs in soybean. Cereal rye is the most common cover crop grown in the Midwest due to its winter hardiness and short life cycle. The high C:N ratio of cereal rye compared to legume or brassica cover crops results in a slow degradation of the residues; thereby, increasing the duration of weed suppression. This along with a greater biomass accumulation makes cereal rye an ideal cover crop candidate. Another non-chemical, cultural strategy to suppress weeds and complement herbicide efficacy is the use of narrow-row vs. wide-row soybean. Growers need research-based information on how to best integrate these two strategies for managing herbicide-resistant waterhemp in soybean.
A field study was conducted (2019-2020) at the ISU Research and Demonstration Farm near Ames, IA to quantify the impact of cereal rye cover crop and soybean row spacing (15 inch vs. 30 inch) on the glyphosate-resistant waterhemp seed bank. The previous crop was corn, with three levels of waterhemp control achieved by:
- A marginal herbicide program (two herbicide sites of action); 27 fl oz/acre Dual II Magnum PRE followed by 32 fl oz/acre Roundup PowerMAX POST.
- An aggressive herbicide program (three herbicide sites of action); 2 fl oz/acre Sharpen + 2.5 fl oz/acre Zidua SC PRE fb 32 fl oz/acre Liberty SL + 23 fl oz/acre Dual II Magnum POST.
- An aggressive integrated program (three herbicide sites of action) plus harvest weed seed control at corn harvest (no weed seed input).
The three programs resulted in three different levels of weed seed production.
After corn harvest, cereal rye was drill seeded (60 lb/acre) in the 2nd week of October, 2019. Soybean (Enlist E3 beans) was planted into the standing rye cover crop at a 30-inch or 15-inch row spacing on May 22, 2020. On the same day, cereal rye (at anthesis stage) was terminated with 32 fl oz/acre Roundup PowerMAX, and 27 fl oz/acre Dual II Magnum was applied to provide early-season residual control of waterhemp. Cereal rye biomass at the time of termination averaged 4600 lb/acre. To examine the potential of cover crop and narrow row soybean on waterhemp control, no POST herbicide was applied in the soybean phase of the study.
The aggressiveness of the prior year’s corn herbicide program had a strong impact on waterhemp infestation in the soybean crop. Waterhemp emergence in soybean was reduced by 75% with the aggressive two-pass herbicide program (three sites of action) plus harvest weed seed control compared with the marginal herbicide program in the previous year (Figure 1). The rye cover crop reduced waterhemp emergence (density) by 30% and waterhemp growth (size and biomass) by up to 75% through July (Figure 2). Reducing the soybean row spacing from 30 to 15 inches reduced waterhemp emergence by 15% and waterhemp growth by 50%. (Figure 3).
The integration of these tactics (Figure 4) resulted in a significant suppression of waterhemp even with limited herbicide inputs in the soybean phase of the rotation. For instance, an aggressive weed control program in corn followed by a rye cover crop and narrow-row soybean showed 87% less waterhemp emergence, compared with the treatment that had marginal weed control in corn, no cover crop and 30-inch soybean row spacing. Soybean yield will be recorded at harvest in the fall 2020 to determine the effects of cover crop, row spacing, and weed competition.
The ISU Weed Science program is also researching cover crop termination timing by herbicide interactions to develop integrated weed management tactics and methods to integrate harvest weed seed control technologies to manage herbicide-resistant waterhemp in Iowa soybean production.
Disclaimer: This article is for education purpose only. Mention of a specific product should not be considered as approval, nor should failure to mention a product be considered disapproval. Read the product label before using any herbicide.
Figure 1. Waterhemp density in soybean with marginal (left) vs. aggressive weed control program plus harvest weed seed control (right) in previous year’s corn.
Figure 2. Waterhemp density in soybean in the absence (left) vs. presence (right) of a cereal rye cover crop terminated at the anthesis stage.
Figure 3. Waterhemp density in soybean planted in 30-inch (left) vs. 15-inch (right) wide rows.
Figure 4. Effect of integrating cover crop and reduced row spacing on waterhemp density in soybean.
Crops: SoybeanCover CropCategory: WeedsTags: cereal ryeCover cropSoybeanwaterhempweed suppression
This is the time of year to begin scouting for Palmer amaranth (Amaranthus palmeri) in Iowa crop fields. While Palmer amaranth has been identified in more than half of Iowa’s counties, new identifications have waned since the widespread introductions in 2016. Palmer amaranth is still a species to watch out for in every Iowa crop field. Minnesota recently reported finding the weed in a county previously not known to have infestations – thus the weed is still on the move. A native of the American southwest, Palmer amaranth is more competitive than common waterhemp (Amaranthus tuberculatus), a pigweed native to Iowa. Both species are known for fast development of herbicide resistance, prolific seed production (>500,000 seeds possible), and prolonged emergence.
The addition of Palmer amaranth to Iowa’s noxious weed law as of July 1, 2017 highlights the importance of this weed to Iowans and its potential impact on Iowa agriculture. Early identification is key to eradicating this weed from fields. Eradication cannot happen without vigilance, early detection, and appropriate response soon after it invades an area. Palmer amaranth is reaching the stage where distinguishing it from waterhemp is much easier due to the presence of flowers. In addition to fields where Palmer amaranth was found previously, other priority areas to scout include farms that utilize feed and bedding from southern states, fields receiving manure from those farms, and farms where out-of-state equipment has been used.
Palmer amaranth and waterhemp lack pubescence (hair) on stems and leaves, while other common amaranth (pigweed) species have hair on stems or leaves. Early in the growing season, Palmer amaranth is difficult to differentiate from waterhemp due to the high variability in both species. Leaves on Palmer amaranth often have a petiole longer than the leaf blade, this is the most reliable vegetative trait to differentiate the two species. Leaves on Palmer amaranth are often clustered tightly at the top of the plant. Palmer amaranth often has a denser canopy than waterhemp (Figure 2).
Figure 1. Palmer amaranth leaf with a petiole longer than the leaf blade. Folding the leaf over at the base is the fastest way to check for this trait.
Figure 2. Waterhemp's open canopy (left) compared to Palmer amaranth's denser, leafy canopy (right).
Palmer amaranth and waterhemp produce male and female flowers on separate plants. Identifying males from females should be relatively simple due to the small, black seed produced by female flowers and the presence of pollen on male plants. Female Palmer amaranth are easy to distinguish from waterhemp due to long, sharp bracts (Figure 3) surrounding the flowers (Figure 4). If you discover this weed, steps should be taken to remove all female plants to prevent seed production.
Figure 3. Comparison of a female Palmer amaranth flower and a female waterhemp flower.
Figure 4. Female Palmer amaranth with long terminal inflorescences.
Continued vigilance is imperative to slow the speed with which Palmer amaranth invades our state. If you observe a plant that you think may be Palmer amaranth, please don’t hesitate to contact Bob Hartzler at 515-294-1164 or firstname.lastname@example.org or Meaghan Anderson at 319-331-0058 or email@example.com.Category: WeedsTags: palmer amaranthPalmer amaranth identificationscoutingWeedsweed scouting
Most people are probably aware of the unsolicited mailing of seed packets from China and other countries. The Iowa Department of Agriculture and Land Stewardship (IDALS) has issued guidelines on how to deal with the situation if you should receive one of these packages. The following statement was made by IDALS.
Why do we care?
1. The seed is unlabeled, and could be an invasive plant that does not currently exist in the US.
2. The seed may contain seed-borne diseases that we don’t have in the USA.
3. Some packets appear to have an unknown seed treatment applied (seed treatments are usually an insecticide and/or fungicide). Because the packets are unlabeled we don’t know what the compounds are, nor how dangerous they could be to human health.
4. Seed is an agricultural commodity that is regulated for quality and content by the USDA as well as State Departments of Agriculture.
We are asking you to do the following:
1. Do not plant the seed;
2. Do not open the packets;
3. Please let the Iowa Department of Agriculture and Land Stewardship know you have received the seed; IDALS – (515) 281-5321
4. Please retain the packaging and seed, as we will make arrangements to collect the seed for investigative purposes and then arrange for appropriate disposal.
Why do we think this is happening?
We think this could be a brushing scam where for whatever reason they are using seed, and sometimes, packages that contain nothing. We suggest changing your passwords in your online shopping accounts.
IDALS Press Release. July 28, 2020Category: WeedsTags: invasive weedsunsolicited mailingsregulatory
Late summer can provide a window of opportunity to seed perennial forage legumes and grasses, whether you want to establish a new forage crop or need to fill in bare and thin spots in an existing forage stand. To help improve the chances for a successful late summer seeding of forages, consider the following.
Field preparation prior to seeding
- It is suggested to take soil samples and fertilize based on fertility needs of the field. Testing is the only way to really know the fertility levels and needs in a field.
- Have problematic weeds under control.
- Check herbicides used previously in the field as many can have residual soil activity that could prevent establishment of new forage seedings if the crop rotation restriction intervals are not observed. A good resource to check herbicide labels is www.cdms.net/label-database.
Timing of seeding and environmental conditions
- Ideally, we want 6 to 8 weeks of growth after emergence before we have a killing frost in the fall; therefore, the recommended window for late summer forage seedings ranges from early August to early September, but it varies slight depending upon location in the state as listed below.
- Northern Iowa: Early to mid-August
- Central Iowa: Mid-August to late August
- Southern Iowa: Late August to early September
- One of the biggest challenges with late summer seedings is having adequate moisture available for germination and seedling establishment. This is especially a concern for western Iowa this year. If conditions are dry, a late summer seeding is not recommended.
- Loose seedbeds dry out very quickly. Deep tillage should be completed several weeks ahead of seeding so rains can settle the soil before final seedbed preparation. A cultipacker or roller is an excellent last-pass tillage tool. The soil should be firm enough for a footprint to sink no deeper than 3/8 to 1/2-inch.
- If moisture is a concern, interseeding and no-till forage seeding can help conserve moisture, provided weeds are controlled prior to planting.
- Seeding depth is important since most forage species are small-seeded. Final seed placement should be no deeper than ½-inch for heavier soils and ¾-inch for lighter soils. If seeding with a drill, it is recommended to set the drill at the ¼-inch depth. You should see approximately 10% of the seed visible on the soil surface. If you are seeing a smaller amount, the seed is being placed to deep, and you need to adjust your seeding depth.
- Thickening up alfalfa stands with more alfalfa is only recommended within 12 to 15 months of the original planting date due to autotoxicity.
- If seeding a legume, make sure the legume seed has fresh inoculum of the proper rhizobium.
- Do not harvest late summer perennial forage seedings this fall. It is best to let them establish and develop winterhardiness.
Late summer can be an excellent opportunity to thicken up forage stands or start new seedings; however, use the above tips to help ensure success. For more information on late summer forage seeding or to get specific questions answered, please reach out to your local Iowa State University Extension and Outreach field agronomist.Crop: Biomass and ForageCategory: Crop ProductionTags: late summer seedingalfalfaperennial grasses
As parts of Iowa enter severe drought on July 14 (D2, US Drought Monitor), I encourage you to scout for twospotted spider mites in crops. Twospotted spider mites can increase whenever temperatures are greater than 85°F, humidity is less than 90 percent, and moisture levels are low. These are ideal conditions for the twospotted spider mite and populations are capable of increasing very rapidly.
A hand magnifying lens is recommended to scout for twospotted spider mites (< 1/60 inch long). They can be mistaken for specks of dirt with the naked eye (Photo 1). Twospotted spider mite larvae have six legs, whereas nymphs and adults have eight legs. Mites can be collected by shaking leaves onto a white piece of paper, and then look for moving mites. Twospotted spider mites are typically a cream or green color when feeding on corn or soybean. They can also be an orange to red color when conditions are unfavorable for their growth.
Photo 1. Twospotted spider mite. Photo by Frank Peairs, www.ipmimages.org.
Twospotted spider mites often aggregate at the field edges, especially if there are weeds surrounding the border. Eventually they may disperse with the wind to develop a field-wide infestation. I encourage people to look at the edge rows first to see if mites can be found. If their presence is confirmed, then estimate populations throughout the field by walking a “Z” or “W” pattern.
Twospotted spider mites begin feeding on the bottom of the plant, and move to the top as the plant’s health deteriorates. Although they lack wings, twospotted spider mites disperse with the wind to move from dying plants to areas with healthy plants. Therefore, it important to scout healthy areas of an infested field that are downwind from damaged areas. Symptoms of twospotted spider mite injury will initially appear as small yellow dots or stipples on the lower leaves of the plants. Prolonged feeding will cause infested leaves to turn completely yellow, then brown, and eventually the leaf will die and fall from the plant. Webbing often is visible on the edges and underside of leaves, and is an indication of prolonged colony feeding (Photo 2). Twospotted spider mites are capable of reducing soybean yield by 40-60 percent when left untreated.
Photo 2. Heavy twospotted spider mite infestation on corn. Photo by Adam Sisson, Iowa State University.
Exact treatment thresholds for spider mites in corn and soybean do not exist. Instead, the decision to treat should take into consideration how long the field has been infested, mite density including eggs, mite location on the plant, moisture conditions and plant appearance. A general guideline for soybean is to treat between R1-R5 (i.e., beginning bloom through beginning seed set) when most plants have mites, and heavy stippling and leaf discoloration is apparent on lower leaves (Photo 3). Foliar insecticides are recommended in corn from R1-R4 (i.e., silking through dough stage) when most plants have mites at or around the ear leaf and 15-20 percent leaf discoloration.
Photo 3. Twospotted spider mite injury on soybean. Photo by Whitney Cranshaw, www.ipmimages.org.
Bruce Potter and Ken Ostlie (University of Minnesota) developed a rating scale to help make treatment decisions:
0 – no spider mites or injury observed
1 – minor stippling on lower leaves and no premature yellowing observed
2 – stippling common on lower leaves and small areas on scattered plants with yellowing observed
3 – heavy stippling on lower leaves with some stippling progressing into the middle canopy and leaf yellowing and some leaf loss observed; mites scattered in the middle and top canopy [Economic threshold]
4 – lower leaf yellowing readily apparent and leaf drop common; stippling, webbing and mites common in the middle canopy; mites and minor stippling present in upper canopy [Economic injury]
5 – lower leaf loss common and yellowing moving to the middle canopy; stippling and distortion of upper leaves common; mites in upper canopy observed.
Organophosphates are the recommended insecticidal chemistry for twospotted spider mite control (e.g., dimethoate and chlorpyrifos). Most pyrethroids are not effective against twospotted mite except bifenthrin. Insecticides may not kill the eggs, thus a treated field should be scouted 7-10 days after application to determine if a second application is necessary. As always, refer to the label for the appropriate rates and re-entry intervals. To improve application coverage and contact of mites, consider increasing the water carrier volume. Treating field edges may be a cost effective option if heavy spider mite populations are restricted to edge rows.
Treatment of twospotted spider mites may not be required when temperatures drop below 85 degrees and humidity levels are greater than 90 percent for an extended time, because a naturally-occurring fungus can control populations. Mites that are infected by the fungus will appear brown, and will not move on the piece of paper used for scouting.
For more information, visit these websites:
Two-spotted spider mite management in soybean and corn (University of Wisconsin)
Crops: CornMinor cropsSoybeanCategory: Crop ProductionInsects and MitesTags: pestmitesscoutingIPM
This year we have received many inquiries about potato leafhopper (Photo 1) in soybean and alfalfa. Although they are present in Iowa every year, populations are higher than in 2018 and 2019. Usually, potato leafhoppers are only considered a pest of alfalfa in Iowa, but they do feed on soybean, too. Potato leafhoppers prefer smooth leaves and are usually repelled by varieties with pubescence (hairs).
Photo 1. Potato leafhopper adult (top) and nymph (bottom). Photo courtesy of Penn State College of Agricultural Sciences.
In soybean, potato leafhopper nymphs can be mistaken for soybean aphid because they are similar in size and color. These hoppers have white eyes, tapered abdomens and do not have cornicles (Photo 1). Potato leafhoppers inject a toxic saliva into the plant while feeding with a piercing-sucking stylet. This style of feeding destroys plant cells and inhibits the transport of fluids within leaves. In soybean, potato leafhoppers feed along the mid-veins, causing the leaf to curl or twist. In severe cases, soybean and alfalfa can exhibit “hopper burn” (Photo 2). Feeding injury creates stunted plants with leaves that turn yellow along the margins and may eventually fall off. Soybean usually outgrows symptoms of hopper burn, but new alfalfa stands and regrowth following cutting may be severely affected. Since hopper burn in soybean can be similar to potassium deficiency, it is important to scout to confirm the presence of potato leafhopper.
Photo 2. Potato leafhopper feeding is known as “hopper burn.” Note the characteristic v-shaped yellowing along the margins of the leaves (ignore hole). Photo by Rebecca Vittetoe.
While walking through soybean, hoppers are easily disturbed and will attempt to hop or fly away from you. We recommend using a sweep net to estimate the number of potato leafhoppers per sweep and assess population changes over the growing season. Treatment options in alfalfa are based on stand size, market value, and hopper density. See this ICM News article for an economic threshold table. No such thresholds exist for potato leafhoppers in soybean.
Typically, potato leafhopper injury is not enough to warrant an insecticide treatment in soybean. Field evaluations have only been able to document yield loss from this pest when heavy infestations cause severe stunting on very young plants. However, when heavy infestations occur, plants are more susceptible to severe injury when:
- Planting is delayed into June and soybean is still in the early vegetative stages
- Variety has smooth leaves or has little pubescence
- Drought conditions occur
We do not typically recommend treating soybean for potato leafhoppers alone. The exception is if severe hopper burn is present AND plants are under additional stress, such as drought. In these cases, many foliar insecticides are labelled for use against potato leafhopper in soybean. The greatest concern for soybean and alfalfa growers in Iowa at this point in the season is potato leafhopper injury combined with dry conditions. According to the U.S. Drought Monitor, 7% of Iowa is in a moderate drought and 42% of Iowa is abnormally dry (Figure 1).
Figure 1. The western half and the eastern “nose” of Iowa are abnormally dry. Data courtesy of the United States Drought Monitor (droughtmonitor.unl.edu).
Make sure to scout for potato leafhopper while dry conditions persist to minimize their impact. Adults and nymphs can be managed with pyrethroid insecticides, but exercise caution when applying pyrethroids in areas where soybean aphid is present. Some soybean aphid populations have evolved resistance to pyrethroid insecticides. Check the insecticide label and follow all labelled rates to ensure effective management.Crops: SoybeanBiomass and ForageCategory: Insects and MitesTags: potato leafhoppersmanagement of potato leafhoppersscouting potato leafhoppers
An ongoing public concern is the loss of nutrients from agricultural land in the corn belt. In Iowa, nitrogen and phosphorus losses from farm fields are driven by a variety of factors. Since the mid-twentieth century, statewide corn and soybean acres have increased as extended rotations, hay, and pasture declined. Compared to perennial crops and small grain rotations, corn-soybean and continuous corn rotations are leaky systems. They require increased fertilizer rates creating vulnerability to nutrient loss, have a lower capacity for capturing and holding nitrogen (N) during wet conditions, and lack surface cover to prevent soil erosion and phosphorus (P) loss during heavy rain events. These nutrient losses contribute to local stream and river impairments, create challenges for small communities in maintaining safe nitrate levels in drinking water, and add significantly to the size of the dead zone in the Gulf of Mexico.
Addressing nutrient loss in Iowa agriculture
Figure 1. Agricultural land use over time in Iowa. Data: United States Department of Agriculture National Agricultural Statistics Service.
To address Iowa’s nutrient contributions to the Gulf hypoxic zone, the Iowa Nutrient Reduction Strategy (INRS) established goals for reducing N and P loss from agricultural nonpoint sources by 41% and 29%, respectively. The INRS Science Assessment identified a number of conservation options that reduce N and P loss ranging from in-field fertilizer and soil management practices to strategic conversion of row crop acres to perennial systems. The INRS identifies these practices as follows.
- In-field practices – annual management practices including cover crops, reduced and no-tillage, and fertilizer management.
- Edge-of-field and erosion control practices – structural practices or vegetation that prevent nitrate and/or eroded soil from leaving the field and entering nearby surface water or subsurface drainage. These practices include bioreactors, saturated buffers, terraces, and nutrient removal wetlands.
- Land use change – practices that incorporate additional crops or convert row crops to perennial vegetation. These practices include extended rotations, conversion to pasture or prairie, and perennial bioenergy crops.
The Iowa Nutrient Reduction Strategy Annual Report is published each year to document the change in statewide efforts toward meeting the INRS goals, including acres of various conservation practices such as cover crops, tillage, bioreactors, and more. Below are some of the findings of that assessment.
- Cover crops planted in Iowa increased from 379,000 acres in fall 2011 to 973,000 in fall 2016, according to the newly available 2017 United States Department of Agriculture (USDA) Census of Agriculture.
- Based on the USDA Census of Agriculture, annual corn and soybean planted acres have remained relatively consistent since the 1980s, with some fluctuation. Preliminary analyses of the USDA Cropland Data Layer suggest that perennial agricultural acres – including pasture, hay, and acres enrolled in CRP – have decreased over time, with approximately 4.3 million acres in 2018.
- No-till acreage increased from 6.9 million acres in 2012 to 8.2 million in 2017, according to the Census of Agriculture.
- By the end of the 2018 calendar year, there were an estimated 27 bioreactors and 13 saturated buffers installed through cost-share programs, treating an estimated 2,000 acres or more.
- Iowa has 86 nitrate-removal (i.e., CREP) wetlands that treat 107,000 acres. An additional 30 wetlands are currently under development for completion in the coming years.
- Since 2011, approximately 22.5 million feet of terraces have been constructed using state cost-share funds. These terraces treated 174,000 acres of land and reduced P losses by 40 tons in 2018.
Meeting the goals of the INRS requires changes on every acre of Iowa farmland. One scenario calls for an estimated 10.5 million acres of no-till and strip-till, 12.5 million acres of cover crops, 7,600 nutrient removal wetlands, and 120,000 bioreactors and saturated buffers. In comparing these numbers to the 2019 assessment of practices, we have a lot of work ahead us to reach the goals. Numerous resources and technical and financial assistance programs are available to assist farmers, landowners, and their advisers select, implement and manage conservation practices successfully.Tools for getting started
With a range of conservation practice options to choose from, it can be difficult to decide which practice(s) is right for you and where to start. The Conservation Systems Best Practices Manual and decision support tools were developed with these challenges in mind to help farmers, landowners, and their advisers make sound decisions and have successful conservation practice implementation experiences. The manual outlines recommendations for in-field and edge-of-field practices including cover crops, no-till, strip-till, multi-year crop rotations, prairie strips, bioreactors, saturated buffers, and nutrient removal wetlands. The manual was developed using a cropping systems approach and includes planting, nutrient management, pest and disease management, and harvest tips and considerations for the in-field practices. Download the free manual from the ISU Extension Store website.Financial incentives
To help offset the cost of getting started, the statewide cost-share program through the Iowa Department of Agriculture and Land Stewardship Water Quality Initiative Program is offering $25 per acre for first time cover crop farmers and $15 per acre for farmers who have tried cover crops in the past. First time no-till or strip-till adopters are eligible for $10 per acre and farmers using nitrapyrin nitrification inhibitor with fall fertilizer are eligible for $3 per acre. Funding is limited to a maximum of 160 acres per farmer or landowner. Applications can be submitted through your local Soil and Water Conservation District office.Crop ProductionTags: conservationwater qualityIowa Nutrient Reduction Strategy
The Ag Container Recycling Council (ACRC) sponsors a free program to recycle clean triple-rinsed or pressure-rinsed pesticide containers up to 55 gallons in size. Refer to the ACRC Container Preparation Checklist for more information on preparing containers. Under the ACRC program, G. Phillips and Sons, LLC, located in Stanwood, IA collects and recycles containers in Iowa. For more information, visit G. Phillips and Sons, LLC. To set up a pickup, call G. Phillips & Sons at 563-942-0391 or email them at firstname.lastname@example.org.
Several companies will recycle larger containers, such as mini-bulk and intermediate bulk containers (IBCs). They may have different requirements for collection and costs. Some of the companies serving Iowa include:
G. Phillips and Sons, LLC
Mauser Packaging Solutions
Schuetz Container Systems, Inc.
Ticket Service – Collection and Reconditioning of IBCs
For information on cleaning larger containers, refer to this document.Category: Pesticide EducationTags: pesticide safetypesticide containerspesticide container recyclingrecycle
Soybean gall midge was confirmed as an economic pest of soybean in 2018. Worldwide, it is only known to occur in five states in the Midwestern US (Figure 1). Research began in 2019 to monitor the emergence of adults and incidence of larval feeding, as well as management options for the pest. This year, soybean gall midge adults were first collected on June 12 and larvae were detected in soybean on June 23.
Figure 1. Soybean gall midge distribution from 2018 and 2019. Map by Justin McMechan, University of Nebraska-Lincoln.
Adult soybean gall midge is a small fly, approximately ¼ inch in length. They have long white and black banded legs and an orange abdomen (Photo 1). It is unlikely that you will see adult soybean gall midge in the field.
Photo 1. Adult soybean gall midge, female on the left. Photo by Mitchell Helton, Iowa State University.
The larvae of soybean gall midge are maggots, which lack legs and any distinct features. They go through three stages, or instars. First instars are small, translucent and difficult to see with the naked eye. Second instars are larger and milky-white, or light orange. Mature, third instars are bright orange and very active (Photo 2).
Photo 2. Soybean gall midge larvae turn orange as they mature. Note discolored plant tissue near feeding sites. Photo by Mitchell Helton, Iowa State University.
The larvae are the damaging stage of the pest. Larvae feed on the tissues within the soybean stem, disrupting nutrient and water movement within the plant. At first, the stem may become dark and discolored near the soil line (Photo 3). Initial symptoms can be confused with fungal pathogens, like Phytophthora and Rhizoctonia. A gall may form, which appears as a swelling, discoloration or outgrowth of the stem. Infested plants will quickly wilt and die or break off at the site of feeding.
Photo 3. Split soybean stems near the soil line to look for larvae and feeding injury. Photo by Mitchell Helton, Iowa State University.
Soybean gall midge overwinters as mature larvae in fields that were planted with soybean the previous year. Adults emerge from the soil and, since they are weak fliers, seek out the nearest soybean plants to lay eggs. Infestations typically begin at the field edge and expand to the field interior over the summer.
Fields adjacent to a field that was injured by soybean gall midge the previous year should be prioritized when scouting. In the first few rows of soybean, look at the base of plants for a dark discoloration at or above the soil line. Carefully peel back the layers of the discolored portion of the stem with your fingernail to look for white or orange larvae. A hand lens can aid in seeing larvae inside stems.
Unfortunately, there are no research-based effective management strategies to suppress larvae at this time. We are working to develop insecticide and other cultural tactics to reduce yield losses. Anecdotal observations show early-planted fields are more susceptible to infestations and subsequent severe plant injury.
If you suspect you have a soybean gall midge infestation, send us photos or contact your regional field agronomist to aid in confirmation. As we continue to monitor the spread of this pest throughout Iowa and the Midwest, please contact us if you have an infestation and you are in a county that is not represented in Figure 1. Real-time soybean gall midge activity in the US is reported on this regional website.Crop: SoybeanCategory: Insects and MitesTags: soybean gall midgegall midgescoutinggall midge larvaesoybean pest
Farmers have enjoyed the benefits of Bt corn since its introduction in 1996, particularly “in the bag” transgenic protection from insect pests and the yield loss they inflict. European corn borer (ECB), Ostrinia nubilalis, was particularly challenging and the target of the first Bt hybrids. The adoption of Bt corn in the U.S. prompted a widespread suppression of ECB. Even so, ECB still shows up in conventional cornfields in Iowa and can be a devastating pest.
In 2019, approximately 15% of corn in Iowa and 17% of corn in the U.S. did not contain a Bt trait and would be susceptible to ECB infestation (Figure 1). Non-Bt corn hybrids have been of interest recently due to lower seed costs of non-Bt corn amid low crop values. For farmers who opted out of Bt corn this year, scouting for ECB (and other corn pests) will be essential. A comprehensive guide to understanding ECB and its association with other pests is available from the ISU Extension Store and can serve as a management guide.
Scouting for European corn borer in conventional corn
Figure 1. Percent of corn acres planted to hybrids with only Bt traits or stacked (Bt + herbicide tolerance) traits in a) Iowa and b) the U.S. Data courtesy of USDA-NASS.
A review of the life cycle and identification of ECB can be found here. ECB larvae feed on almost any part of the corn plant except the roots. On leaves, feeding can appear as shotholes or a windowpane effect. They can also tunnel into the stalk, midrib of the leaf, or ear shanks. The result of ECB feeding injury is poor ear development, broken stalks, and dropped ears. Reduced grain quality from ear molds can occur due to ear feeding increasing infection by pathogens.
Figure 2. Feeding by European corn borer larvae can appear as shotholes on the leaves. Photo by Adam Sisson.
There are typically two generations of ECB in Iowa, and each generation has unique scouting requirements to ensure effective management. Life stages and behaviors can be predicted based on degree day accumulation from the date when adults are first captured in the spring, which is called the biofix. Therefore, monitoring for adults is essential for timely scouting and treatment decisions.First generation: scout for larvae
Corn should be scouted for first generation larvae once susceptible plants reach V6 to determine the number of live larvae. Look for feeding injury in the whorl and on the youngest leaves; plants without these symptoms are unlikely to contain larvae. For every 40-50 acres, 20 consecutive plants should be sampled in five areas to obtain a representative sample of 100 plants. If more than one hybrid is planted in the field, consider each hybrid as a separate field for scouting and treatment determination. A cost-benefit analysis table can help determine if an insecticide is economically justified to control an infestation in vegetative corn (page 9 in the publication). Early-planted fields will likely have higher populations of first-generation ECB.Second generation: scout for egg masses
Adults produced from the first generation begin laying eggs when the corn is around VT-R1, and egg-laying lasts for about 20 days. Degree days can be used to determine when egg-laying begins (page 5 in the publication), and scouting should occur 8-10 days after that date. Eggs are laid primarily on the underside of leaves. Use the same sampling plan as before (20 consecutive plants in five areas of the field) and count egg masses on seven leaves: the ear leaf plus three leaves above and below the ear leaf. After R3, when silks are brown, scouting for new egg masses is unnecessary if the ET was not reached.
To determine if an insecticide is economically justified, use the cost-benefit analysis table for reproductive stage corn (page 10 in the publication). Treatments for second-generation ECB must be timed accurately to be effective. Applications should be made soon after egg hatch but before larvae enter the leaf axil, sheath, collar, ear tip, or before they bore into the stalk or ear shank. Depending on the duration of egg-laying, a second application may be warranted. Fields at VT-R1 and with green silks are most attractive to female moths. Late-planted corn will typically have the largest population of second-generation ECB.Crop: CornCategory: Crop ProductionInsects and MitesTags: european corn borerBt corncorn borercrop scouting
Several Iowa State University Extension and Outreach Field Agronomists have reported fields with high numbers of grubs this spring. There are a number of grub species in Iowa, including Japanese beetle. With warm temperatures accelerating insect development, expect adult Japanese beetles to begin emergence in southern Iowa counties this weekend (Figure 1). The emergence is about 7-10 days ahead of the last few years. Literature shows Japanese beetle adults need about 1,030 growing degree days (base 50°F) to complete development and will continue emergence until around 2,150 degree days.
Plant Injury and Management
Figure 1. Growing degree days accumulated (base 50°F) for Japanese beetle adults in Iowa (as of June 11, 2020). Adults begin emergence around 1,030 degree days. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.
Japanese beetles have a wide host range that includes many species of fruit and vegetable crops, ornamentals, and field crops. On corn, silk clipping can interfere with pollination. Consider a foliar insecticide during tasseling and silking if: there are 3 or more beetles per ear, silks have been clipped to less than 1/2 inch, AND pollination is less than 50% complete. On soybean, adults prefer to feed between the leaf veins and can ultimately consume most of the leaf. The treatment threshold for Japanese beetle in soybean is 30% defoliation before bloom and 20% defoliation after bloom. It is important to note most people overestimate plant defoliation. Migrating adults could reinfest the field in after knocking down an initial population. I recently published a review article for Japanese beetle if you want to learn more about this corn and soybean pest.Category: Insects and MitesTags: japanese beetlejapanese beetle injuryinsect emergence
Corn rootworm egg hatch in Iowa occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. In 2020, the expected hatching date will be behind the average due to cool spring temperatures. Development is driven by soil temperature and measured by growing degree days. Research suggests about 50% of egg hatch occurs between 684-767 accumulated degree days (base 52°F, soil). Most areas in Iowa will reach peak corn rootworm egg hatch in 5-7 days (Figure 1).
Figure 1. Accumulated soil degree days in Iowa as of June 9, 2020. Expect 50% corn rootworm egg hatch between 684-767 degree days. Map data courtesy of Iowa Environmental Mesonet, Iowa State University Department of Agronomy
To predict corn rootworm egg hatch for your area based on degree day accumulation, use the ISU Agronomy Mesonet website. Set the start date to January 1 of the current year, use the current date for the end date, and make sure the plot parameter is set to “soil growing degree days (base = 52).” Be aware that some locations are having technical difficulties with the soil temperature probes this year.
A severe corn rootworm larval infestation can destroy nodes 4-6; each node has approximately 10 nodal roots. Root pruning interferes with water and nutrient uptake and make the plant unstable (Photo 1). A recent meta-analysis showed a 15% yield loss for every node pruned back to 1/5 inches.
Photo 1. Severe root pruning by corn rootworm larvae can dramatically impact yield. Photo by Erin Hodgson, Iowa State University.
Regardless of agronomic practices used to suppress corn rootworm (e.g., crop rotation, Bt hybrids, or soil-applied insecticides), every field should be scouted for corn rootworm root injury. Continuous cornfields and areas with Bt trait performance issues are the highest priority for inspection. Looking at corn roots 10-14 days after peak egg hatch is encouraged because the feeding injury will be fresh. Assess corn rootworm feeding and adjust management strategies if the average injury is above 0.5 on the ISU 0 to 3 Node Injury Scale. Also consider monitoring for adult corn rootworm to supplement root injury assessments. Aaron Gassmann, Iowa State University corn entomologist, has a webpage for additional corn rootworm management information including an interactive node-injury scale demonstration and efficacy evaluations.Crop: CornCategory: Insects and MitesTags: corn rootwormInsectsegg hatchcorn rootworm egg hatch
Alfalfa weevils aren’t the only insect pest being found in alfalfa fields this spring. Reports of aphids, particularly cowpea aphids and pea aphids, have been made around the state. This article will discuss identifying the common aphid species found in Iowa as well as scouting and management recommendations for aphids in alfalfa.Aphid species
In general, aphids are soft bodied and pear-shaped insects. They have a piercing-sucking stylet (mouthpart) and feed on sap within the plant phloem. The two cornicles, which are like tailpipes, on the tip of the abdomen is an important diagnostic feature to distinguish aphid species. Table 1 lists the four common aphid species found in Iowa. Additional information on these different species can be found online.
Table 1. Common alfalfa aphid species found in Iowa.
Size and color description
Blue alfalfa aphid
3/16”; blue with black cornicles
March – June
1/8”; shiny black with black cornicles
¼”; pale green or pink with dark cornicles
April – November
Spotted alfalfa aphid
1/8”; pale yellow with dark spots on abdomen and short cornicles
May – OctoberAphid scouting, thresholds, and management
The good news is harvesting alfalfa is an excellent method to control aphids as very few aphids will survive. Many fields have already been harvested or will soon be harvested. Additionally, natural enemies, like ladybeetles or damsel bugs, can help keep aphid populations in check. As the alfalfa starts to regrow below are guidelines on how to scout and monitor fields for aphid pressure.
To scout for aphids, count the number of aphids on at least 30 alfalfa plant stems. Average the number of aphids per stem. Since populations can be spotty across fields, it is recommended to sample multiple areas across the field when doing the stem counts. The economic thresholds for aphids are summarized in Table 2.
Table 2. Economic thresholds for pea aphids, blue aphids, cowpea aphids, and spotted alfalfa aphids. (Source: IPM-58).
Blue aphids and Cowpea aphids/stem
Spotted alfalfa aphids/stem
Spraying before the economic threshold is met can lead to an aphid resurgence. Only spray once the threshold is reached and if the field is not ready to be harvested. If an insecticide is warranted, always read and follow the label instructions. Pay attention to pre-harvest interval when spraying, and make sure to use sufficient volume and pressure when spraying to ensure contact with aphids on the lower parts of the plants.
Crop: Biomass and ForageCategory: Insects and MitesTags: aphidsalfalfa pestsforage pestsalfalfa weevils cowpea aphidspea aphids
A sweep net can be used to check for the presence of aphids in alfalfa fields. (Photo taken July 3, 2003 by Brian Lang).
There are several different species of plant-parasitic nematodes that feed on corn in Iowa. These microscopic worms usually are present in low numbers and do not affect yields. But the potential for plant-parasitic nematodes that feed on corn to cause yield reductions is real and warrants attention.Nematodes on corn - it’s complicated
Iowa State University professor and nematologist Dr. Don Norton found nearly two dozen species of nematodes feeding on corn in Iowa in the 1960s, 1970s, and 1980s. Despite there being a wide diversity of species, one aspect that is consistent for all of the nematodes is that yield loss on corn always is preceded by development of above-ground symptoms such as stunting or chlorotic foliage. This means that sampling to determine if damaging nematode population densities are present need only be done in areas of fields where corn plants are showing symptoms.
Below are recommendations on how to collect samples for assessing the potential damage and yield loss caused by nematodes that feed on corn.What type of sample should be collected?
Up to corn growth stage V6: collect soil and root samples
- Use a soil probe, angle underneath a corn plant and collect soil cores that are at least 12 inches long (see Figure 1).
- Collect 20 or more soil cores to represent an area.
- Collect soil cores from within the root zone of plants with symptoms of damage. Combine (but do not mix) soil cores and place in a sealed plastic bag labeled with permanent marker.
- Also collect, with a shovel, the root mass from 4 to 6 plants with symptoms of damage (see Figure 2). Take care not to strip off the smaller, seminal roots. The tops of the plants can be cut off and discarded. Place the roots in a sealed plastic bag labeled with permanent marker.
- Protect samples from physical jarring and keep samples cool (at or below room temperature).
Figure 1. Collecting a soil core from corn to determine the presence and number of plant-parasitic nematodes.
Figure 2. Young corn plant collected to determine the presence and number of plant-parasitic nematodes in the root tissue.
Corn growth stage V6 through R3 (milk): collect only soil samples
- Use a soil probe, angle underneath a corn plant and collect soil cores that are at least 12 inches long (see Figure 1).
- Collect 20 or more soil cores to represent an area.
- Collect soil cores from within the root zone of plants showing symptoms of damage. Combine (but do not mix) soil cores and place in a sealed plastic bag labeled with permanent marker.
- Protect samples from physical jarring and keep samples cool (at or below room temperature).
Corn growth stage R4 (dough) and later: sampling not recommended
There is not a reliable relationship between damage or yield loss and the number of nematodes present in soil and roots once the corn crop reaches the R4 growth stage.Where to send samples?
Samples for nematode analysis can be sent to some private soil-test laboratories in Iowa and surrounding states. Check with the lab to determine if they process nematode samples for corn before sending the samples. Many university plant disease clinics and nematode diagnostic labs also process samples for nematodes on corn. A list of the university laboratories and their contact information is available online.
Iowa State University’s Plant and Insect Diagnostic Clinic processes samples for nematodes that feed on corn. The test is called the complete nematode count. Samples sent to the ISU Clinic should be accompanied by a Nematode Sample Submission Form (ISU Extension Publication "PIDC 32"). There is a $35 per sample processing fee ($40 per sample for out-of-state samples).Managing nematode damage on corn
If damaging population densities of nematodes are found in a corn field, there is nothing that can be done during the season to slow the build-up of nematode numbers and lessen the yield loss. Management options for future corn crops include using soil-applied Counter® 20G nematicide and/or seed treatments such as Aveo™, Avicta®, Escalate, Nemastrike™, Trunemco™, and Votivo®.Crop: CornCategory: Insects and MitesTags: nematodesscoutingsamplescorn pests
Iowa’s early planting season means that pests like the soybean cyst nematode (SCN) also are off to a quick start this year, which could result in a greater risk of severe damage from SCN throughout the growing season. This nematode is a major yield-reducing pathogen of soybean and is widespread across Iowa and other Midwestern states. Research conducted in recent years indicates that many fields have not been checked for SCN.Quick and cheap check for SCN
One of the easiest and cheapest ways to check a field for the presence of SCN is to dig soybean roots with a spade, shake the soil from the roots, and look for small, white, round objects on the roots. These objects are SCN females and each one contains 200 or more eggs. As shown in the figure below, SCN females are much smaller and lighter in color than the nitrogen-fixing nodules that form on healthy soybean roots.
Soybean root with white SCN females (yellow arrows) and nitrogen-fixing nodules (blue arrows).
Checking soybean roots in this manner also is a quick and easy way to gauge whether a resistant variety is effectively controlling SCN. Only a few SCN females should be seen on the roots if resistance is working effectively. But if the SCN population present in a field has built up virulence on the resistance genes in the soybean variety, there will be many SCN females present (as shown in the image immediately below).
SCN visible on roots dug through mid August
White SCN females on roots of a resistant soybean variety.
The SCN females fade from white to yellow, then become tan and eventually brown within a few days to a week as the female dies and the body wall hardens to form a cyst around the eggs within. It is almost impossible to see brown SCN cysts on soybean roots dug from a field with the unaided eye. Some white adult females should be apparent on roots of soybeans growing in SCN-infested soil no matter when the roots are dug.
Fields can be checked for SCN by carefully digging and observing roots through June, July, and into mid August. In warm summer soils, SCN can complete a generation in four weeks, ending with formation of new females on roots. The newly formed SCN females occur on younger roots and as the season progresses, those new roots are forming deeper in the soil and father from the stem of the plant. Therefore, it is advised to dig deeper for roots in July and August to look for SCN females.Learn more about SCN biology, management, and testing
There is a large amount of information available online about the biology and management of SCN and guidelines on how to scout fields for SCN and how to collect and submit soil samples for SCN testing. Check out www.soybeancyst.info, www.soybeanresearchinfo.com, and www.thescncoalition.com.Crop: SoybeanCategory: Plant DiseasesTags: SCNsoybean cyst nematodescoutingresistance
In 2019, numerous field edges were infested with common stalk borer. Tracking degree days is a useful tool to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications, if needed, are only effective when larvae are migrating and exposed to the insecticide. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Much of Iowa has reached this important benchmark (Figure 1), and therefore scouting for migrating larvae should begin now to make timely treatment decisions.
Figure 1. Degree days accumulated (base 41°F) for stalk borer in Iowa (January 1 – June 2, 2020). Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.
Female moths prefer to lay eggs in weedy areas in August and September, so managing weeds (especially brome grass and giant ragweed) earlier in the growing season can help make fields less attractive. Additionally, long-term management requires mowing grassy edges and roadsides around fields so that females will not lay eggs in that area during the fall. Using burndown herbicides before corn planting can force stalk borers to move and infest emerging corn.
Stalk borers tend to re-infest the same fields, so prioritize fields with a history of stalk borers for scouting first with extra attention to the field edges. Finding “dead heads” in weeds is an indicator of stalk borers in the area. The larvae are not highly mobile and typically only move into the first four to six rows of corn. Young corn is particularly vulnerable to severe injury; plants are unlikely to be killed once they reach V7 (Photo 1).
Photo 1. Stalk borer larvae can shred corn leaves and destroy the growing point.
Larvae excrete a considerable amount of frass pellets in the whorl or at the entry hole in the stalk, which is a good indication that larvae are present. Also, look for new leaves with irregular feeding holes that may indicate the presence of larvae. To prevent stand loss and determine if an insecticide treatment is warranted, look for larvae inside the whorls and determine the percentage of plants infested. The use of an economic threshold (Table 1), first developed by Iowa State University entomologist Larry Pedigo, will help determine justifiable insecticide treatments based on market value and plant stage. Young plants have a lower threshold because they are more easily killed by stalk borer larvae.
Table 1. Economic thresholds (expressed as percent of infested plants) for stalk borer in corn, based on market value, expected yield, and leaf stage.
If an insecticide is warranted based on stalk borer densities, the application must be well-timed to reach exposed larvae before they burrow into the stalk. Target applications at peak larval movement, or 1,400-1,700 degree days (base 41°F). Applying insecticides after larvae have entered the stalk is not effective. Since larvae are not highly mobile, consider border treatments. Make sure to read the label and follow directions, especially if tank-mixing with herbicides, for optimal stalk borer control.
For more information on stalk borer biology and management, read a Journal of Integrated Pest Management article by Rice and Davis (2010), called “Stalk borer ecology and IPM in corn.”Crop: CornCategory: Insects and MitesTags: stalk borerscoutingdegree daysstalk borer larvaestalk borer management
Iowa State University (ISU) research has evaluated corn and soybean response to preplant potassium (K) fertilizer placement methods and starter since the middle 1990s. These results have been used for developing guidelines in Extension publication PM 1688. In recent years, excessive fall and spring rainfall sometimes has precluded the normal K preplant fertilization. Therefore, growers and crop consultants have been asking if sidedressed liquid K fertilizer could alleviate deficiency or be a good complement to preplant K fertilization, as is commonly the case for nitrogen. A crop response to P sidedressing is unlikely, and preplant or starter fertilization is preferred, because sufficient P needs to be available very early for seedlings shoot and root growth and early cell multiplication to attain the hybrid and soil yield potential. This is not so much the case for K, however, which explains why very often there is corn response to starter P but only occasionally for K when soil-test K is very deficient.
To study in-season K application, twelve 2-year field trials were conducted with corn to evaluate how sidedressed injected liquid K fertilizer interacts with pre-plant broadcast K fertilization and soil test K levels at affecting grain yield and tissue K test levels. Six trials were established in 2017 and six in 2018. The trials were at central, northeast, northern, southeast, southern (McNay), and southwest (Armstrong) ISU research and demonstration farms. Initial soil-test K across the trials ranged from the Very Low to the Optimum interpretation categories in the ISU Extension publication PM 1688 “A General Guide to Crop Nutrient and Limestone Recommendations in Iowa”.
Treatments were four broadcast preplant rates of 0, 45, 90, and 135 lb K2O/acre using granulated potash fertilizer (0-0-62) and two K sidedress rates using potassium-acetate liquid fertilizer (0-0-24). All treatments were replicated four times. The preplant treatments were broadcast in the spring two to three weeks before planting to soil with soybean residue that had no fall tillage. With the exception of one trial managed with no-tillage, all other plots were field cultivated before planting corn. After corn emergence all plots were subdivided into two subplots to apply either 0 or 45 lb K2O/acre, which was injected to the center of every inter-row to a depth of 3 to 4 inches at the V5 to V6 growth stage. Corn leaf tissue K concentration was analyzed in ear-leaf blades sampled at the R1 (silking) growth stage.
Results shown in Figure 1 are averages across nine trials that showed a statistically significant responses of leaf K concentration and grain yield. Two trials were affected by severe drought and corn at another trial was severely affected by strong wind and green snap. The graphs summarize the responses to applied K, although the magnitude of the responses varied across trials as affected by the initial soil-test K level and weather.
The yield and leaf K concentration increases from the broadcast preplant K application were within expectations given initial soil-test K levels and the rates applied. The largest yield increases were in soils testing Very Low, for which 130 lb K2O/acre is recommended, and the smallest in soils testing Optimum, for which only a removal-based rate is recommended (see publication PM 1688). Sidedressed K fertilization increased average grain yield and ear-leaf K concentration further with all preplant K rates at all sites, but the apparent small increases for the 135-lb K2O/acre preplant rate were not statistically significant.
Figure 1. Corn grain yield and ear-leaf K concentration responses to broadcast preplant K fertilization and liquid K fertilizer sidedressed at the V5-V6 growth stage. Vertical red (preplant) or blue (sidedress) lines indicate the increases by applying a similar 45-lb rate sidedressed or preplant.
The results in Figure 1 show that a broadcast preplant rate of 45 lb K2O/acre increased both grain yield and leaf K concentration much more than a similar sidedressed K rate. This was observed in most trials, even those testing Optimum. Therefore, sidedressed fluid K for corn at the rate used may be an option when recommended preplant K rates based on soil testing cannot be applied before planting (fall or spring). Results do not support, however, purposely withholding or reducing preplant K rates to be complemented by K sidedressing.Crop: CornCategory: Crop ProductionSoil FertilityTags: potassium applicationpotassium fertilizationpreplant fertilizationCorn
With planting wrapping up and crops beginning to emerge, now is the time to start scouting fields regularly throughout the growing season for any potential issues. Scouting fields and monitoring crops throughout the growing season can help you make more informed management decisions and stay on top of potential issues that may come up during the growing season. Even if some issues cannot be fixed, regular scouting can help us better understand what happened in the field and make adjustments to reduce issues in the future. This article will discuss the basics of crop scouting as well as crop scouting tools and resources.
Crop Scouting Basics
Normal vs. Not Normal: It is important to be able to distinguish between what a normal plant looks like (above and below-ground) and what a not normal plant looks like. Understanding and recognizing crop growth and development stages provides key insight in determine if things are on track or are being influenced by environmental conditions.
Additionally, other key symptoms that tell us something is not normal with a plant include the plant color; crinkling of leaves; loss of leaf tissue; wilting; and pinched, stunted, or deformed root systems.
Normal, healthy looking corn seedling next to two stunted and discolored unhealthy corn seedlings. When scouting being able to distinguish between normal and not normal helps to alert us to potential issues. Photo courtesy of Rebecca Vittetoe.
Being able to distinguish between normal and not normal helps alert us to if there is maybe an issue going on in a field. If you don’t know why it’s not normal, that’s totally fine. There are resources and people you can turn to in order to determine what’s going on in the field.
Scouting Procedure: Start with an overview of the field looking for any unusual patterns or odd areas that may require a closer investigation. When walking through the field, it is also recommended to have a general scouting planning and walk through the field in a pattern whether that be a “Z” or “W” pattern, or a diamond pattern to make sure you get a good observation of what’s happening across the field. Change up the route you take through the field each time.
As you walk through the field, stop several different points along your route and take a closer look at the plant level. It is suggested you take a closer look at 5 to 15 plants at each stop for a minimum of 50 to 100 plants per field.Crop Scouting Tools/Resources
The following is a list of useful crop scouting tools:
- A clipboard or tablet that can be used to take notes while walking through the field.
- Pen and paper to record information, as well as electronic devices such as cameras, smartphones, or other mobile devices.
- A hand lens or mobile digital microscope to see small insects or disease lesions normally not as visible to the naked eye.
- Sample collection bags, vials, or a cooler useful for collecting diseased plants or insect specimens to be professionally identified.
- A pocket knife or hawkbill knife used to split or cut pods, stalks, or stems while searching for pests.
- A trowel or spade (recommend a flat bottom spade) to sift through soil surrounding plants to look for insects or to dig up roots.
- A sweep net to collect insect samples.
- A soil probe and soil sample bag to collect soil samples for nematode or nutrient tests.
- Measuring tape to collect stand counts and measure patterns within a field to identify potential causes of abiotic symptoms related to tillage, sprayer, or planter widths.
- Personal protective gear is sometimes required and always useful. For example, special protective eyewear, long-sleeved shirts, or other gear may have to be used when scouting.
There are a variety of publications and other resources that can be useful to help identify pests or other potential issues in the field. The ISU Extension Store has links to purchase or download numerous resources for crop scouting. An online compendium of crop scouting resources can also be found on the ISU Extension Integrated Pest Management resource page.
The ISU Plant and Insect Diagnostic Clinic is available for you to submit samples for to help diagnosis what is going on in your field. Please contact the clinic at email@example.com with sample inquiries.
Reach out to your local ISU Extension and Outreach field agronomist for more resources and information.Category: Crop ProductionTags: crop scoutingscouting basicsscouting tips
Every spring, alfalfa growth and development differs due to variations in climatic, variety, stand age and other crop production factors. With the 2020 growing season being off to a cooler than normal start, alfalfa growth is also off to a slower start this spring. This is a good reminder that while calendar date is one method used to determine when to harvest first crop alfalfa, it is not the best method to use. Instead, the PEAQ method (Predictive Equations for Alfalfa Quality) developed by the University of Wisconsin does a better job.
The PEAQ method uses alfalfa stand height and maturity stage (vegetative, bud, or bloom) to estimate the relative feed value (RFV). In general, it is recommended to harvest alfalfa at about 150 RFV for first trimester dairy and calves, 135 for stocker cattle, and 120 for lactating beef cattle. First crop alfalfa standing in the field can drop three to five points of RFV per day. The steps on how to use the PEAQ method to determine when to make the first crop of alfalfa are listed below.
Note that while PEAQ does a good job of estimating the RFV, under the best harvest conditions 10-20% of the forage dry matter will be lost at harvest. This amounts to approximately 15 RFV points for haylage and 25 RFV points for hay. Therefore, to end up with 150 RFV alfalfa, harvest the crop when PEAQ measurements estimate a RFV of 165 for a haylage harvest and 175 for a hay harvest. And, of course, take into account the weather forecasts. Don’t wait on a little more stem growth if it’s going to cause a rain delay.Steps for using PEAQ to determine when to take first crop alfalfa
Step 1. Choose a representative two square foot area in the field.
Step 2. Determine the stage of the most mature stem in the area by using the definitions at the top of Table 1.
Step 3. Measure the tallest stem in the area. The tallest stem may not be the most mature stem. Measure the stem from the soil surface to the tip of the stem; not to the tip of the leaf. Straighten the stem for an accurate height measurement. Based on stem maturity and stem height, use Table 1 to estimate the RFV of standing alfalfa crop.
Step 4. Repeat steps 1-3 in five representative areas across the field.
Step 5. To estimate harvest quality, subtract 15-25 RFV units to account for harvest losses during the haylage or hay harvest process, respectively.
Step 6. Determine optimum harvest time using the PEAQ estimate, livestock forage quality needs, considerations of upcoming weather forecasts favorable for harvest, and the general assumption that RFV drops three to five points per day.
ISU Extension maintains a PEAQ website that includes a fact sheet to explain how to use the PEAQ method to determine when to harvest first crop alfalfa. This website also includes postings of PEAQ values from some alfalfa fields across Iowa being monitored by ISU Extension and Outreach staff. Follow the progress in these reports but remember conditions can vary field-by-field. Therefore, it is recommended to take PEAQ measurements in your own fields to best estimate first crop harvest to help target the quality of forage you wish to achieve.Crop: Biomass and ForageCategory: Crop ProductionTags: alfalfaPEAQalfalfa harvestalfalfa growthPEAQ method
Black cutworm (BCW) is a migratory pest that arrives in Iowa with spring storms each year. BCW moths lay eggs in and near crop fields, and larvae can cut corn seedlings or feed on leaves. Even though crops were planted earlier this year than previous years, cold temperatures may slow growth and allow BCW larvae to coincide with early vegetative corn that is vulnerable to BCW injury.
BCW is a sporadic pest, making it essential to scout to determine whether management is required. When to scout for BCW larvae is based on when a “significant flight” of moths arrives in Iowa; accumulating degree days after this significant flight can predict when BCW eggs will hatch and larvae will be active. A flight is considered significant when eight or more BCW moths are captured in a wing-style pheromone trap over two consecutive nights.
39 BCW traps were established by 36 cooperators in 34 counties around the state this year. These cooperators monitor pheromone traps and report moth captures to track moth movement in Iowa. BCW moths were reported almost immediately after cooperators began checking traps April 1. Moth captures continued through April, with one peak flight occurring in Washington County (SE) on April 12 and subsequent peak flights in Washington County and Marshall County (C) on April 28. Even though only two counties reported significant flights, statewide BCW moth captures increased dramatically during the week of April 26.
Figure 1 shows the predicted cutting dates for BCW for each crop reporting district. These cutting dates are predicted using actual and historical degree day data combined with the occurrence of peak flights during April. Predictions are made using the most accurate data available to us. BCW trapping will continue throughout May, and any additional peak flights that occur will be included in our weekly ICM Blog updates.
Figure 1. Estimated black cutworm dates for each Iowa crop reporting district based on peak flights during April.
Capturing BCW moths in a pheromone trap does not necessarily mean there will be economic infestations in a particular location. Scouting fields is the only way to determine if BCW are present and whether management is warranted.Identification
BCW larvae have grainy, light grey to black skin and four pairs of fleshy prolegs at the end of the abdomen (Figure 2). There are pairs of dark tubercles, or bumps, along the sides of the body. The tubercles are used to distinguish BCW from other similar cutworm species, like dingy cutworm (Figure 3), that rarely cause economic injury in corn. On each body segment, the tubercle closest to the head is about 1/3 the size of the tubercle closest to the rear for BCW; the corresponding tubercles on each segment for dingy cutworm are roughly the same size. The Field Crop Insects publication from the ISU Extension Store can aid in identification of other cutworm species.
Figure 2. Black cutworm larvae have grainy and light grey to black skin. Photo by Adam Sisson.
Scouting for black cutworm
Figure 3. Black cutworm (left) can be distinguished from other larvae, such as dingy cutworm (right), by the dark tubercles along their bodies. For black cutworm, the tubercles nearest the head on each segment are about 1/3 the size of the tubercle closest to the rear. Corresponding tubercles on dingy cutworm are about the same size. Photos by Adam Sisson.
Poorly drained, low lying, or weedy fields may have a higher risk of BCW injury. Additionally, fields near natural vegetation, fields with reduced tillage, or fields with cover crops may be at higher risk. Green cover crops are attractive to egg-laying females. Late-planted or slow-growing corn are typically smaller and more vulnerable to larval feeding. Some Bt hybrids provide BCW suppression (hybrids with Vip3A and Cry1F proteins; see The Handy Bt Trait Table), but larvae can still cut young plants.
Fields should be scouted weekly (every 7-10 days) until corn reaches V5. Begin scouting at least a few days before estimated cutting dates; early scouting is important because local larval development varies due to weather variation within a climate division, and additional significant flights could prolong the arrival of BCW larvae to a field.
Examine 10 corn plants in five areas of the field (50 total plants). Look for wilting, leaf discoloration or damage, and missing or cut plants (Figure 4). BCW larvae sometimes drag cut plants under soil clods to continue feeding during the day. Flag areas with suspected BCW feeding and return later to assess further injury. Take note of plant growth stage and the size of larvae in the field; this will help determine how long larvae may continue to injure plants. Larvae can be found by carefully excavating the soil around a damaged plant – BCW larvae are nocturnal feeders and will hide in the soil during the day. Remember to watch for indications of other early season pests such as wireworms, white grubs, and seedcorn maggot.
Thresholds and management
Figure 4. Black cutworm is known for completely severing corn seedlings. However, injury from black cutworm larvae usually begins above the soil surface. Leaf feeding can occur (left), or larvae can severely damage or kill plants (right). Photo on left copyright Marlin Rice; photo on right courtesy of Jon Kiel.
The generic economic threshold for BCW in corn is 2-3% of plants cut when larvae are less than ¾ inch long and 5% of plants cut when larvae are greater than ¾ inch long. However, this threshold can be adjusted depending on corn price, final corn stand, and input costs. A dynamic threshold calculator for BCW may be used to aid management decisions.
Preventative insecticide treatments are a questionable practice. Rescue treatments are usually the most efficient and economic approach to managing BCW since it is a sporadic pest. Scout to determine that larvae are still present in the field before spraying insecticides for BCW.
Will BCW survive freezing temperatures?
We have experienced a lot of fluctuating temperatures, including some freezing temperatures after black cutworm arrived in the state. Young larvae, pupae, and adults are not expected to survive when exposed to subfreezing temperatures. Eggs and older larvae (4th to 6th instars) are the most cold-hardy stages; they may survive weeks below freezing. If eggs are laid but have not yet hatched, they will likely survive but development may be slowed and cutting may occur later than predicted.Report larvae!
If you see any fields with BCW larvae or injury while scouting, please let us know by sending a message or photo to firstname.lastname@example.org. This information will help us refine cutting predictions and scouting recommendations in the future.
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