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How Are Nematodes Impacting My Corn Crop?

Summary

• Corn nematodes can reduce corn yield potential without visible symptoms.
• Nematodes can feed on the surface of the roots (ectoparasite) or within the roots (endoparasite) depending up on the species.
• Soil and root samples are required to determine nematode presence as well as species identification.

Introduction

Estimating yield loss due to nematode infestations can be difficult. Though yields may have been excellent, top-end yield potential may have been reduced because nematode feeding restricted nutrient uptake that could have increased yield potential. In 2022, the estimated losses to nematodes in the United States and Ontario, Canada were 54.2 million bushels.1 Individual nematode species vary regarding their damage potential. As an example, needle and sting nematodes can cause extreme damage when there is only one nematode per 100 cubic cm (cm3) of soil. Table 1 shows damage thresholds for different nematode species. It is important to understand that these are damage thresholds only and are NOT calibrated on a response to a nematode control product.

Corn growing under very good to excellent environmental conditions can be plagued with nematode feeding; however, symptoms may not
be apparent, which sets the stage for hidden yield loss. Below is the complied list of above and below-ground symptoms caused by nematodes that can be confused with other agronomic factors (disease, fertility, insect, or herbicide injury).

Above-ground Signs

• Thin stands
• Stunted plants
• Uneven plant height
• Uneven tasseling
• Leaf yellowing
• Small ears and kernels

Below-ground Signs

• Swollen roots
• Black or dark brown dead spots on roots (necrotic lesions)
• Limited fine roots and branches (Figure 1)

Root and soil sampling is the only way to determine the presence of damaging nematode populations in a field. Soil and root samples are required because some nematodes live within the roots (endoparasites) and others live only in the soil and feed externally on the roots (ectoparasites).Field history and soil type play a huge role when soil sampling for nematodes. If a field has a known nematode history, then sampling timing can be dictated by the previously identified species. However, because of cooler soil temperatures, early-season sampling is generally recommended because nematodes are more likely to be closer to the surface.

If the field is at least 80% sand, sampling should be conducted prior to the V6 growth stage (6 leaves with exposed collars) because sting and needle nematodes can go several feet deep when the temperature in sandy soil increases. Regardless of soil type, if sampling is completed early in the season (by V6), 4 to 6 plants should be dug with roots intact. Collected samples should be representative of 40 acres or less. However, if nematodes are suspected in identifiable problem areas, soil samples should be collected from the problem and the non-problem area for comparison.


Figure 1. Sting nematode damage to corn roots. Picture courtesy of and used with the permission of Clemson University-USDA Cooperative Extension Slide Series, Bugwood.org

 

Sampling Procedures for Sandy Fields

• Sample the perimeter of large, suspected areas instead of the center.
• The root zone should be probed 6 to 8 inches deep at an angle.
• About 20 soil core samples should be collected and mixed to get at least a two-cup sample.
• Double bag soil and plants separately in sealable zipper-top plastic bags.
• Samples should be handled gently to help avoid damaging nematodes.
• Refrigerate samples until shipping.
• Pack samples in a leak-proof container with soft packing material.
• Complete a submission form for the respective diagnostic laboratory.
• Samples should be shipped early in the week.
• Nematodes must be alive for proper analysis.

Sampling Procedures for Non-Sandy Soil Type Fields

• If sampling is completed by V6 growth stage, 4 to 6 plants should be collected by digging the roots carefully.
• If sampling after V6, no additional roots are necessary providing soil cores are collected from the root zone.
• Collected samples should be representative of 40 acres or less. If nematodes are suspected in identifiable problem areas, soil samples should be collected from the problem and the non-problem area for comparison.

Nematode Management

There are two management strategies for damaging nematode populations: 1) crop rotation with non-host crops and 2) using available soil-applied nematicides to keep the population under check. There are no rescue treatments available. One yield-protection estimate for the use of a nematicide when damaging populations of root-knot, stubby-root, and sting nematodes are present is 10 to 40 bu/acre or more.6

Article Link

Sources:
1Mueller, D. Wise, K. and Sisson, A. 2023. Corn disease loss estimates from the United States and Ontario, Canada – 2022. Crop Protection Network. https://cropprotectionnetwork.org/publications/corn-disease-loss-estimates-from-the-united-states-and-ontario-canada-2022).
2Tylka, G. 2009. Common corn nematode Characteristics. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/cropnews/2009/08/common-corn-nematode-characteristics
3Jagdale, G. and Brewer, C.L. 2013. Guide for interpreting nematode assay results. Circular 834. University of Georgia Extension. https://extension.uga.edu/publications/detail.html?number=C834
4Tylka, G. 2007. Nematodes in corn production: A growing problem? Integrated Crop Management. (IC-498) (1) Iowa State University.
https://crops.extension.iastate.edu/encyclopedia/nematodes-corn-production-growing-problem
5Jackson-Ziems, T. 2015. Corn nematode sampling. CROPWATCH. University of Nebraska-Lincoln.
https://cropwatch.unl.edu/corn-nematode-sampling
6Lee, R.D. (editor), Noland, R., Harris, G., Porter, W., Prostko, E., Buntin, D., Kemerait, B., Sumner, P., Toews, M., Rabinowitz, A., and Smith, A. 2019. A guide to corn production in Georgia. Corn disease and nematode management update for 2019. Pg. 100. Georgia Agricultural Commodity Commission for Corn. University of Georgia Extension. https://grains.caes.uga.edu/content/dam/caes-subsite/grains/docs/corn/2019-Corn-Production-Guide.pdf
Additional Source: Tylka, G. 2009. Quick facts about corn nematodes. Integrated Crop Management. https://crops.extension.iastate.edu/cropnews/2009/04/quick-facts-about-corn-nematodes
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1211_131401

Tips for Summer Corn Scouting

*This content was previously published by Corteva Agriscience.

No matter when your customers were able to get into the field for planting this spring, regular scouting can help set the stage for a successful corn yield come harvest.

Getting into the field on a regular basis after planting will improve the timing on important crop protection decisions. Is there a new flush of weeds that needs to be managed? Will postemergence herbicides need to be applied sooner than anticipated? Are there any nutrient deficiencies? Are there any new insect or disease pressures? All these questions can be answered and addressed with regular scouting.

Scouting should occur multiple times throughout the growing season, but there are times when it’s more critical, says Joe Bolte, Market Development Specialist, Corteva Agriscience.

 

Pests to watch this year

With lengthy emergence periods, waterhemp and Palmer amaranth present an annual challenge — calling for a herbicide program approach that includes multiple modes of action for effective control. Bolte says, “Depending on your geography and planting date, waterhemp or Palmer amaranth may need to be controlled in every herbicide pass — not just the postemergence application.”

On the flip side, your customers in areas with heavy rainfall may not have had a chance to get their preemergence herbicides down in time. If this is the case, they may consider reallocating those preemergence herbicide dollars to create a more powerful postemergence pass.

Bolte also says that tar spot should be on everyone’s radar. Scouting the corn plant’s canopy will help determine if a fungicide application is warranted.

 

Scouting resources available

There are several free resources available to help customers with in-field corn scouting. “Many universities will put together scouting guides or calendars for common pests. Use these to determine when weeds, disease and insects are most likely to emerge in your geography,” Bolte says.

You also can contact your local Corteva Agriscience representative and download our Corn & Soybean Disease ID Guide and Corn Weed Scouting Checklist for more detailed information.

 

Key corn scouting timing

 


Corn & Soybean Disease ID Guide

 


Corn Weed Scouting Checklist

Article Link

™ ® Trademarks of Corteva Agriscience and its affiliated companies.
© 2024 Corteva. Groundwork – June 2024

Spray Timely and Early for More Effective Weed Control

*This content was previously published by Corteva Agriscience

When looking at a weed, its overall height can be deceptively short. How is that possible? Because, to a herbicide, the weed’s height is not a linear measurement from the ground to the top of the plant. When a herbicide is fighting a weed, that fight takes into account every inch of the weed. It includes every point of growth that is on the plant, coming out of the main stem.

Corteva Agriscience Herbicide Trait Specialist Steve Snyder illustrates this in a video on application practices. (Use the QR code to check it out.)

In the video, Snyder measures off a single 8” waterhemp weed and pulls it from the ground. He then breaks off each branch growing from the main stem of the plant and lays them end to end on the ground and measures the length of all the sections of the plant as a whole. The total length comes out to 33″. Snyder explains how, to the herbicide, this is a 33″ weed, not an 8″ weed. He says that this is one reason why it is so important to apply herbicide early and in a timely manner. The herbicide has a much greater chance of being effective when the plant is 6” tall or less, because the weed has far fewer growth points than a larger, more mature weed.

Snyder’s demonstration makes a good point. Weeds that are left to grow taller than 6” make the job of the herbicide just that much tougher. Catching weeds early is an important aspect of good weed control and helps ensure the treatment is as effective as possible.

Article Link

® Trademarks of Corteva Agriscience and its affiliated companies. © 2024 Corteva.

Management of Western Bean Cutworm in Corn

 

Biology

There is a single generation per year. Larvae overwinter in the soil and moths can emerge as early as June and last until September, but the peak emergence period is mid-July. The adult moth is an active flier at night and can be found resting in the whorl of corn during the day. Females can oviposit up to 600 eggs over their life, and the average lifetime production is about 380 eggs. The female deposits eggs on the upper surface of corn leaves during vegetative growth stages, and after tasseling the switches to laying eggs on the leaves closest to the ear or on the ear itself. Newly deposited eggs are bright white and barrel-shaped, and laid with an average of about 50 eggs per mass (Figure 1). Prior to hatching, the eggs become purple (Figure 2), which is caused by the color of the head capsule of the larvae showing through the eggshell. Depending on temperature, egg hatch can occur five to seven days after oviposition.

 


Figure 1. Newly deposited egg mass laid by a western bean cutworm. Note the bright white color. Frank Peairs, Colorado State University, Bugwood.org.

 


Figure 2. Egg mass laid by a western bean cutworm, just prior to hatch. Note the purple color; light-colored eggs are infertile or parasitized. Frank Peairs, Colorado State University, Bugwood.org.

 

Larvae consume their eggshells, and the subsequent feeding behavior of the larvae depends on the developmental stage of the plant. If the corn plant is in the VT stage, the larvae move to the tassel and feed on the tassel tissue and developing anthers (Figure 3). This feeding does not result in economic injury.

If the tassel has emerged, the larvae can be found in leaf axils feeding on dropped anthers and pollen. Larvae will also feed on silks at this stage. Upon the conclusion of pollen shed, larvae move to the ear tip and feed on developing kernels (Figure 4).

Larvae in the early developmental stages have subdued diamond shapes along the back, while mature larvae have brown bands behind the head.

Mature larvae feed on the ear tip and tunnel into the side of the ear to access the kernels. Larvae disperse from the plant where the eggs were deposited to infest neighboring plants, both within and across the row. After completing at least six growth stages in about 55 days, the larvae drop to the soil and burrow to create an earthen overwintering chamber. Depending on soil texture the overwintering chambers can be at a depth of 16 inches in coarse soil, but on average are found about 8 inches deep across soil types. Winter mortality rates under natural conditions are about 60%, with higher rates of survival in coarse-textured soils.

 


Figure 3. First instar larvae feeding on pollen and pollen sacs. Frank Peairs, Colorado State University, Bugwood.org.

 


Figure 4. Western bean cutworm larvae; note the brown bands behind the head. The bands are only present on later larval growth stages.

 

Injury

Injury caused by western bean cutworm larvae is usually randomly distributed across the field as the yield map in Figure 5 indicates, with the red areas being heavily infested. The later growth-stage larvae destroy kernels at the tip of the ear and along the ear. Most larvae are found within five and a half feet of the original plant. This movement to adjacent plants can lead to many injured ears. The entry point through the husk—caused when larvae tunnel into the ear—can allow entry to pathogens, resulting in ear rots and possible mycotoxin production. Ear tip feeding may be confused with corn earworm injury, but while there is usually only one corn earworm located on each ear, plants infested with western bean cutworm often have multiple larvae feeding on a single ear. Direct kernel consumption equates to an average loss of just less than four bushels per acre to 15 bushels per acre.

 


Figure 5. Yield map of field infested with western bean cutworm. Red areas are heavily infested.

 

Management

Preventative tactics

The Bacillus thuringiensis (Bt) protein Vip3A is currently the only Bt protein that helps to provide control of the western bean cutworm. Corn products with Trecepta® Technology contain the Vip3Aa20 protein and can help provide control. Other cultural practices such as altering planting date and tillage to destroy the pupal cells are of limited value.

Responsive tactics

The correct timing of scouting for western bean cutworm can be refined using either pheromone traps near corn fields or a developmental model
that predicts moth emergence. While both tactics may assist in scouting timing, they cannot be used to determine the need for a responsive management tactic. Scouting timing should be focused on the corn developmental stage at mid-June through July. The female western bean cutworm moth prefers to deposit her eggs on plants that are just about to tassel. While oviposition in some years can occur on whorl-stage corn, the larvae do not survive feeding on vegetative tissue alone and need to consume plant reproductive tissue or pollen to complete their development.

Sampling consists of counting the number of egg masses or small larvae on 20 consecutive plants, in five locations throughout the field due to oviposition being random across the field. Scouting should be continued on a five-day schedule until the oviposition period is complete. In years with extreme growth stage variability across the field, oviposition in the field may occur over a longer period.

If the risk of mycotoxins is minimal and the major concern is direct injury, then an economic threshold of 5 to 8 percent of the plants infested with egg masses or small larvae should be used. In areas where mycotoxins are a concern, the lower economic threshold of 5 percent infested plants should be used. In addition, the economic threshold in this situation is additive. For example, if the infestation rate is 2 percent for the first sampling, and five days later
the second sampling found 3 percent of the plants were infested, then the threshold would be reached (2% + 3% = 5%). Additionally, if mycotoxins are
a concern, the addition of a fungicide with the insecticide applied at R1 is recommended.

Insecticide and fungicide recommendations can change, so please consult your chemical provider for registered approved products.

Article Link

Additional Resources
Smith, J.L., Difonzo, C.D., Baute, T.D., Michel, A.P., Krupke, C.H. 2019. Ecology and management of the western bean cutworm (Lepidoptera: Noctuidae) in corn and dry beans—Revision with focus on the Great Lakes region. Journal of Integrated Pest Management, 10: 1-19. https://academic.oup.com/jipm/article/10/1/27/5558144.

 

Legal Statements
Bayer is a member of Excellence Through Stewardship® (ETS). Bayer products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with Bayer’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. Commercialized products have been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Excellence Through Stewardship® is a registered trademark of Excellence Through Stewardship. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. B.t. products may not yet be registered in all states. Check with your seed brand representative for the registration status in your state. Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. IMPORTANT IRM INFORMATION: Certain products are sold as RIB Complete® corn blend products, and do not require the planting of a structured refuge except in the Cotton-Growing Area where corn earworm is a significant pest. Products sold without refuge in the bag (non-RIB Complete) require the planting of a structured refuge. See the IRM/Grower Guide for additional information. Always read and follow IRM requirements. Roundup Ready® 2 Technology contains genes that confer tolerance to glyphosate. Plants that are not tolerant to glyphosate may be damaged or killed if exposed to those herbicides. Insect control technology provided by Vip3A is utilized under license from Syngenta Crop Protection AG. Bayer, Bayer Cross, RIB Complete®, Roundup Ready® and Trecepta® are registered trademarks of Bayer Group. Agrisure Viptera® is a registered trademark of a Syngenta group company. Respect the Refuge and Corn Design® and Respect the Refuge® are registered trademarks of National Corn Growers Associa-tion. All other trademarks are the property of their respective owners. ©2024 Bayer Group. All rights reserved. 1215_67368

Corn Growth Stage and Herbicide Application Postemergence

Key Points

 

Importance of Identifying the Corn Growth Stage

When selecting a POST herbicide or tank mix combination, the weed species present, weed heights, and corn growth stage should be known. Taller corn is generally more sensitive to potential herbicide injury, particularly when nozzles apply directly into the whorl of the plant. Potential injury can be reduced and weed coverage is increased by using drop nozzles in taller corn (generally 24 inches or more).

Growth stages on herbicide product labels are usually indicated as a corn leaf stage or plant height, and sometimes both are listed. The growth stage that is most restrictive should be followed when both corn leaf stage and height are listed on the label. When using a tank mixture, follow the recommendations for the most restrictive label language of the products being used in the tank mix.

 


Figure 1. Corn plants in the V3 growth stage showing 3 visible leaf collars and a plant height of 6 inches measured from the soil surface.

 

Corn leaf stage is determined by counting leaf collars after emerging from the whorl (Figure 1). Leaves that are just emerging from the whorl will not have a visible collar and are not counted. Leaf stages are designated using a “V” (vegetative) to represent each leaf during vegetative development. The first true leaf (coleoptile leaf) on corn is the short, rounded leaf near the soil surface, which is counted as V1. Each successive, visible leaf collar is counted as V2, V3, and all the way to V18, which emerges prior to tasseling. As corn plants grow, the lower leaves can die or tear away, making it difficult to accurately count the collars. Corn generally loses its coleoptile leaf by the time it reaches the V5 growth stage.
To stage older plants, dig up the plant and split the stalk down into the root ball. Find the triangular “woody” base of the stalk and locate the first internode above the base. The woody, horizontal node is the point of attachment for the fifth leaf or collar. For example, if you can count 5 visible leaf collars above this point, the corn plant is in the V10 growth stage.

Plant height is determined by measuring from the soil surface to the arch of the uppermost leaf that is more than 50% emerged (Figure 1). Plant height may not be an accurate determination of growth stage, because adverse environmental conditions can result in corn plants that are physiologically older than their height suggests.

Herbicide product labels provide directions for over-the-top broadcast and directed drop nozzle applications in corn. Labels provide a maximum corn growth stage for broadcast applications, and after which applications should not be made (Table 1). In corn with Roundup Ready® 2 Technology, a broadcast herbicide application of Roundup® brand glyphosate-only agricultural herbicides can be applied up to the V8 growth stage or 30-inch-tall corn, whichever comes first. Drop nozzles should be used for optimum spray coverage and weed control when corn is 24 to 30 inches tall. When corn is 30 to 48 inches tall, only use drop nozzles and avoid spraying into the whorls of the corn plants.

Some labels indicate the minimum corn growth stage before POST applications should be made. For example, Capreno® herbicide can be applied POST when corn reaches the V1 stage up through V7 or 20-inch-tall corn, whichever comes first. Broadcast applications of Capreno® herbicide in corn grown for seed are recommended from the V1 to V5 growth stages.

 

Table 1. Application restrictions for selected herbicides applied postemergence in corn.
Herbicide Product Maximum corn heights and/or growth stages*
Roundup® brand glyphosate-only agricultural herbicides (glyphosate-tolerant corn) V8 or 30 inches over-the-top broadcast 30-48 inches with drop nozzles
Liberty® Herbicide (glufosinate-tolerant corn) V7 or 24 inches over-the-top broadcast

24-36 inches with drop nozzles
Atrazine herbicide 12 inches
2,4-D herbicide 8 inches (use drop nozzles if over 8 inches)
Banvel®/Clarity® Herbicides (dicamba) 8 inches or 5-leaf using 16 oz/acre rate use 8 oz/acre rate at 8-36 inches
Harness® Herbicide, Harness® MAX Herbicide, Harness® Xtra Herbicide, Harness® Xtra 5.6L Herbicide, and Degree Xtra® Herbicide 11 inches
Warrant® Herbicide 30 inches
TripleFLEX® II Herbicide 11 inches
Balance® Flexx Herbicide V2
Corvus® Herbicide V2
Capreno® Herbicide V1-V7 or 20 inches (V1-V5 in seed corn)
Laudis® Herbicide Up to V8 in field or popcorn, up to V7 for sweet corn. Up to V9 in field or popcorn.
DiFlexx® Herbicide V10 or 36 inches, whichever comes first
DiFlexx® DUO Herbicide Directed application when corn is from V7-V10 stages up to 36-inches tall or up to 15 days prior to tassel. Direct sprays should be used if corn leaves prevent proper spray coverage, sensitive crops are grown nearby or when tank mixing with 2,4-D.
Accent® Herbicide V6 or 20 inches, 20-36 inches using drop nozzles
Acuron® Herbicide 12 inches
Acuron® Flexi Herbicide 30 inches
Aim® Herbicide, Shark® Herbicide V8, V8-V14 using drop nozzles
Basis® Herbicide V2 (do not apply to >6 inches tall corn)
Buctril® Herbicide 12 inches
Callisto® Herbicide V8 or 30 inches
Distinct® Herbicide 4-10 inches using 6 oz/acre rate
10-24 inches using 4 oz/acre rate
24-36 inches using 4 oz/acre rate and drop nozzles
Hornet® Herbicide V6 or 20 inches, 20-36 inches using drop nozzles
IMPACT® Herbicide Up to 45 days of corn/silage harvest
Marksman® Herbicide 8 inches
Option® Herbicide V1-V6, V6-V8 using drop nozzles
Permit® Herbicide and Yukon® Herbicide 36 inches
Python® Herbicide V6 or 20 inches
Resicore® Herbicide 11 inches
Resource® Herbicide V2-V10
Resolve® Herbicide V6 or 12 inches
Revulin® Q Herbicide V6 or 20 inches
Status® Herbicide V2 or 4 inches – V10 or 36 inches
Stinger® Herbicide 24 inches
*Where both height and leaf or growth stage are provided, use the most restrictive classification. ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR THE HERBICIDE PRODUCT.

 

POST Application Considerations

Article Link

Sources
Jhala, A. 2017. Consider corn growth stage when applying postemergence herbicides. University of Nebraska. CropWatch. https://cropwatch.unl.edu.
Hager, A. 2018. Corn growth stage and postemergence herbicides. University of Illinois. Pest Management Bulletin. http://bulletin.ipm.illinois.edu.
Bell, J. 2018. Corn growth stages and post emergent herbicide timing. Texas A&M University. AgriLife. https://agrilife.org.
Lingenfelter, D. 2019. Corn herbicide application timings and restrictions. Penn State University Extension. https://extension.psu.edu.
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be considered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Balance® Flexx, Corvus®, Degree Xtra®, Harness® Xtra 5.6L Herbicide and Harness® Xtra Herbicide are restricted use pesticides. Not all products are registered for use in all states and may be subject to use restrictions. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Check with your local dealer or representative for the product registration status in your state. Tank mixtures: The applicable labeling for each product must be in the possession of the user at the time of application. Follow applicable use instructions, including application rates, precautions and restrictions of each product used in the tank mixture. Not all tank mix product formulations have been tested for compatibility or performance other than specifically listed by brand name. Always predetermine the compatibility of tank mixtures by mixing small propor-tional quantities in advance. Permit® is a registered trademark of, and used under license from, Nissan Chemical Industries, Ltd. Balance®, Bayer, Bayer Cross, Capreno®, Corvus®, Degree Xtra®, DiFlexx®, Harness®, Laudis®, Roundup and Design®, Roundup Ready 2 Technology and Design®, TripleFLEX® and Warrant® are registered trademarks of Bayer Group. Liberty® is a trademark of BASF Corporation. IMPACT® is a registered trademark of Amvac Chemical Corporation. All other trademarks are the property of their respective owners. For additional product information call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.BayerCropScience.us. Bayer CropScience LP, 800 North Lindbergh Boulevard, St. Louis, MO 63167. ©2024 Bayer Group. All rights reserved. 1223_122240

How Can Harvest Help Determine Future Insect Pressure in Corn?

While harvesting corn, combine operators should know how to recognize certain insect feeding injuries. Though the insect may no longer be present, injury symptoms may well be noticeable. If symptoms are present, proactive insect management— including scouting—should be considered for the next crop year.

 

Missing plants or skips within row

Early season injury from white grubs or wireworms could cause missing plants or skips within a row. As these insects usually occur in the same fields over time, management tactics should be considered in the next growing season.

 

Random ears are banana shaped or have random discolored kernels

Brown, green, or brown marmorated stink bug feeding is a likely cause of these symptoms (Figure 1). Heavy stink bug pressure early in the season can lead to deformed, banana-shaped ears (Figure 2). Random kernels may have scars, holes in kernel caps, or appear bruised and dark (Figure 3). Kernels may be mottled in appearance, especially close to the tip of the ear. The following crop should be closely scouted for stink bug damage and managed accordingly, especially if the field has a history of damage.

 


Figure 1. Brown stink bug.

 


Figure 2. Banana shaped ears are characteristic of stink bug feeding.

 


Figure 3. Random discolored kernels occur when stink bugs pierce through the husk to feed on developing kernels.

 

Kernels are damaged by larval feeding and/or have fungal growth

Mid- to late-season kernel feeding from corn earworm (Figure 4), fall armyworm, western bean cutworm (Figure 5), and European corn borer (Figure 6) can directly damage corn kernels by feeding on them, and indirectly lead to increased incidence of disease and rot. When kernel feeding begins during the milk stage of kernel development, the leaking milk provides a favorable substrate for fungal growth which can then damage neighboring healthy kernels (Figure 4). Above-ground Bacillus thuringiensis-protected (B.t.-protected) corn products may resist some or all of these insect larvae. However, large moth flights of corn earworm can indirectly damage B.t.-protected corn. These moths may produce unusually high numbers of larvae, potentially leading to cannibalism among the larvae which further allow the surviving larvae to grow to a large enough size to tolerate the B.t. toxin, resulting in subsequent damage.

 


Figure 4. Combined kernel damage from corn earworm feeding and fungal growth on non- B.t.-protected corn.

 


Figure 5. Western bean cutworm larvae.

 


Figure 6. European corn borer larvae.

 

Evidence of incomplete pollination

During pollination, insect feeding on green silks can prevent ovule (potential kernel) fertilization if the pollen tube, which is attached to an ovule, is cut. This can occur when silks are clipped to less than ½-inch long. Although the silk-clipping insects are no longer a threat to a crop being harvested, scouting for grasshoppers, corn rootworm beetles, corn earworm, and Japanese beetles should be conducted the following year (Figures 7 and 8).

 


Figure 7. Western corn rootworm beetles feeding on silks.

 


Figure 8. Japanese beetles clipping silks.

 

Stalk or root lodging

Stalk- and/or root-lodged corn can cause substantial harvest delays and losses. European corn borer (ECB), southwestern corn borer (SCB), and common stalk borer feeding can weaken stalks and increase the potential for lodging via wind and heavy rain. Holes in the stalk rind and ear shanks are evidence of European corn borer feeding (Figure 9, left). Dropped ears with tunneled-out shanks, broken tassels, or missing tassels can also be evidence of ECB feeding.

Stalks cleanly broken off just above the brace roots are characteristic of southwestern corn borer feeding (Figure 9, right). SCB tunnel downward into the brace roots and generally stay low on the stalk.

 


Figure 9. European corn borer with entry hole below the ear (left) and southwestern corn borer with tunnel within brace roots (right).

 

Common stalk borer tunneling usually occurs early season along fence rows, waterways, and other grassy areas (Figure 10). Injured plants can be stunted and have characteristic tillering because the growing point was killed or damaged.

Severe root lodging or goosenecked plants are characteristic of mid-season rootworm feeding. Depending on the growing season, injured roots may have new growth. However, this new growth is unlikely to support the plant in severe wind or heavy rain.

Stalk and root lodging is also caused by pathogens, which can be introduced by ECB, SCB, or corn rootworm feeding. Selecting corn products with B.t. protection for above-ground insects, below-ground insects, or both can help protect the plants from respective insect feeding.

 


Figure 10. Common stalk borer. Picture courtesy of and used with the permission of James Kalisch, University of Nebraska, Bugwood.org.

 


Figure 11. Root lodging can be caused by mid-season corn rootworm feeding.

 

Moldy corn

Corn contaminated by aflatoxin has been infected by either Aspergillus flavus or Aspergillus parasiticus. These molds often occur when insects feed on corn ears during droughty, high-temperature conditions. A felt-like, greenish-yellow to yellowish-brown mold can be found near insect damage on or between kernels (Figure 12). Sampling for Aspergillus can be done during grain loading by passing a cup multiple times within a stream of grain. Multiple samples should be taken, as distribution is not even within the field. Rapid tests are available for in-field testing. It is important to know that Aspergillus may be present without the development of aflatoxin.

 


Figure 12. Ear with insect larval feeding and Aspergillus fungus that may be aflatoxin.

 

Ragged-edged corn leaves or leaves with ragged holes

Leaves with ragged edges or ragged holes (Figure 13) may be evidence of fall armyworm (FAW) feeding pre-tassel. Grasshopper feeding can mimic FAW feeding and is more likely to be seen during harvest than FAW.

 


Figure 13. Ragged leaves and holes caused by fall armyworm.

 

Article Link

 

Sources:
12019. Stink bug kernel injury. The Ohio State University. Troubleshooting Abnormal Corn Ears. https://u.osu.edu/mastercorn/stink-bug-kernel-injury/
Wrather, A., Sweets, L., Bailey, W., Claxton, T., Sexten, J., and Carlson, M. 2010. Aflatoxins in corn. University of Missouri Extension. G 4155.
https://extension2.missouri.edu/g4155
Nielsen, B. and Colville, D. 1988. Stalk lodging in corn: Guidelines for preventive management. Agronomy Guide. Purdue University. AY-262. https://www.extension.purdue.edu/extmedia/AY/AY-262.html.
O’Day, M., Becker, A., Keaster, A., Kabrick, L., and Steffey, K. 1998. Corn insect pests – A diagnostic guide. University of Missouri Extension. https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/16081/CornInsectPests. pdf?sequence=1&isAllowed=y.
Dean, A. and Hodgson, E. Stalk borer. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/encyclopedia/stalk-borer.
Bessin, R. 2019. Fall armyworm in corn. University of Kentucky College of Agriculture, Food and Environment, Lexington, KY. Entfact-110.
https://entomology.ca.uky.edu/files/efpdf1/ef110.pdf
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1215_178659

Billbug Management in Corn

Billbugs are early season insects in field corn. Southern corn billbug (SCB) can cause damage from emergence through the V6 to V8 leaf growth stages of corn in southeastern production areas. This pest damages corn over the entire Coastal Plain of the southern states and up the Mississippi River valley into the Midwest. Maize billbug (MB) is a related species that can be a problem in corn.

Billbug Injury to Corn

Corn seedlings are normally vulnerable to adult billbug damage until seedlings reach the V6 to V8 leaf stage of growth. At that time, stem diameter becomes large enough to help limit adult feeding on meristematic tissues. Seedlings attacked by billbug adults may have one or more of the following symptoms:

 


Figure 1. Typical corn leaf injury by adult billbug.

 


Figure 2. Injury to corn by southern corn billbug grubs.
Picture courtesy of and used with the permission of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.

 

Immature billbugs (grubs) develop within the root crown area and tunnel into the lower stalk. Plants infested with larvae often show no obvious symptoms but may be more susceptible to drought stress and die prematurely. Damage by grubs may also result in a reduced ear size of up to 40%, depending on time of infestation and other stress factors.

Billbug Identification and biology

Southern corn billbug adults are weevils with long snouts that are about ½ inch in length. They are generally ash gray or brownish in color and are usually covered with soil dust, giving the insect a soil-like color (Figure 3).

Overwintering adults emerge during April and May from litter in fields, ditches, hedgerows, and bordering woods. Adults mainly move by crawling but are capable of flight; therefore, the plants on the edge of the overwintering area are more prone to attack. However, injury to corn can occur within a mile of fields where corn was grown and infested the previous season. Weevils can be found feeding on corn stems near ground level. Females lay about 200 kidney-shaped, cream-colored eggs in holes chewed at the base of corn stems. Eggs hatch in 4 to 15 days and the legless, grub-like larvae migrate down the outside of the stem to feed in roots and tunnel into the lower stalk. The grub is cream-colored, 1/8 to 1/2 inch long (3 to 13 mm) and has a distinct reddish-brown head. Normally there is one larva per cornstalk. The grubs complete their development in 40 to 70 days and pupate (July to September) in or around the corn taproot from which they fed. Adults emerge 1 to 2 weeks after beginning pupation and seek overwintering sites.

Maize billbugs have a similar life history and biology as SCB. The MB is a reddish-brown to black snout beetle (Figure 4).

 


Figure 3. Southern corn billbug. Picture courtesy of and used with the permission of Anyi Mazo-Vargas, University of Puerto Rico, Bugwood.org.

 


Figure 4. Maize billbug. Picture courtesy of and used with the permission of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.

 

The adult billbug ranges from 3/8 to 1/2 inch long (9 to 13 mm).2 The weevil hides in the soil during the day and is active at night. The MB overwinters as an adult in soil, grasses, or plant litter, becoming active about the time corn seedlings are emerging. The weevil mainly migrates to corn fields by walking but can fly 0.25 of a mile (0.40 km) or more. The adults feed at the base of the corn plant and the females lay white to gray kidney-shaped eggs about 10 days after feeding begins, in the holes they gouge in the plant stem with their mouthparts. The gouges later appear as a transverse row of punctures in the expanded leaves. A single female can lay 200 eggs or more over a two-month period. Depending on temperature, the eggs hatch in 4 to 15 days. The grubs feed and develop for several weeks in the center of stalks at ground level before moving into the soil to feed in or around the roots. Pupation occurs in the stems, roots, or soil. There is a single generation per year.

Management

Fields that have a history of billbug injury, particularly the margins of these fields, should be scouted for adult injury from seedling emergence to the V6 to V8 growth stages. The timing for scouting is critical because the window to apply an insecticide treatment is limited. Adults are more active in the early morning and evening. They usually hide underneath litter and soil during most of the day. If high numbers of billbugs are found or adult feeding injury is evident on the stem, the entire area should be sampled by walking an M or W pattern. Within the sampled area, examine 20 consecutive plants for feeding damage in 5 locations, for a total of 100 plants. If 5% of emerged seedlings are lost in a full stand of plants, an insecticide application should be considered.

Preventative management tactics that help prevent billbug infestations should be considered and include:

 

Summary

Preventing billbug injury to corn relies on integrated management. Crop rotation and cultural practices that promote rapid and vigorous corn seedling establishment are the critical elements of the plan. Field selection is particularly important in no-till situations where early corn growth can be slow. Rapid, uniform germination and seedling growth can help 1) reduce the time that corn seedlings spend in the most sensitive growth stages for billbug feeding damage and 2) increase seedling tolerance to feeding damage. If corn will be planted in areas with high billbug infestations, a seed-applied insecticide or T-band application of an insecticide may be necessary.

Article Link

Sources
Reisig, D. 2023. Billbug. North Carolina State University. https://corn.ces.ncsu.edu/corn-insect-management/field-corn-insect-pests/billbug/
Purdue Extension Entomology. 2009. Maize billbug – Purdue Fields Crops IPM 2009. Purdue University. https://extension.entm.purdue.edu/fieldcropsipm/insects/maize-billbug.php
University of Illinois Extension & Outreach. Billbug. University of Illinois. http://extension.cropsciences.illinois. edu/fieldcrops/insects/billbug/
 Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

Insect Management Benefits from Corn Seed Treatments – Corn Belt

Introduction

As early as Egyptian agriculture, various materials were used as seed treatments to protect seeds after seeding. Selecting active ingredients for use as seed treatment should consider soil diseases, nematode species present, and early insect pressure. Cultural reasons for using a seed treatment include soil temperature, moisture, early seeding date, crop is for seed production, and expectation of economic return. Seed treatments can help address many problems and there are several different products from which
to choose.

 

Why are farmers embracing seed treatments?

Seed treatments have proven to be a convenient method to battle early-season insects and diseases as well as promoting early-season plant growth. Stand establishment is one of the most important yield contributing factors. Many things can limit stand establishment and corn seed treatments can often help preserve yield potential and grain quality.

 

How can a reduction in pesticide still be effective?

Seed treatments allow a reduction in the active ingredient exposure – approximately a half an ounce released an acre of soil. Active ingredients placement near the seed creates a zone of protection within and surrounding the seed with potentially less impact on the environment. Seed treatments also can reduce or eliminate the number of insecticide foliar sprays due to targeted protection against insect pests. Other benefits growers have the potential to experience with seed treatment use include:

 

What types of corn seed treatments are available?

Different seed treatments are used alone or in combination to help address a number of pests, diseases, and nutrient deficiencies as well as to enhance plant growth. These treatments include insecticide, fungicides, nematicides, and biologicals. Fungicides help to protect against soilborne and seedborne diseases, including Fusarium, Rhizoctonia solani, and Pythium. Biologicals add a new component to seed treatment offerings. Acceleron® BioRise® 360 ST is designed to enhance mycorrhizal spores and promotes mycorrhizal symbioses in the root zone. Insecticide and nematicide offerings vary by trait and class. We describe the pests they control in the following questions.

 

What insect pests can be managed with seed treatments?

Since 2008, in-furrow insecticide treatments have been getting replaced with insecticide-treated corn seed. By 2011, 80% of corn seed was being treated with neonicotinoid insecticide seed treatment. Insecticide seed treatments have been shown to improve corn yield potential. This is especially the case for corn growers in the south where winter temperatures are not low enough to stop insect lifecycles. Growers across the Arkansas, Louisiana, Mississippi, and Tennessee experienced a corn yield benefit of about 11 bu/acre for seed treated with a fungicide plus neonicotinoid insecticide compared to seed treated with fungicide alone.

Even in the Mid-West, soils warm enough for seeding often trigger subterranean insect activity. Infestations are unpredictable between years, and thresholds may not reflect current cost of production or commodity prices. Defense against these infestations becomes a priority to protect the grower’s seed investment. Select active ingredients and seed treatment rates based on the identified pests to help achieve pest control. Insects controlled with a seed treatment such as Acceleron® Seed Applied Solutions with 50 mg active ingredient/seed of Poncho®/VOTIVO® include:

 


Figure 1. White Grub. Photo courtesy of Alton N. Sparks, Jr., University of Georgia, Bugwood.org.

 


Figure 2. Wireworm. Photo courtesy of R.J Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org.

 

 
Figure 3. Seed corn maggot. Photo courtesy of Maiusz Sobieski, Bugwood.org.

 


Figure 4. Black cutworm. Photo courtesy of Roger Schmidt, University of Wisconsin-Madison, Bugwood.org

 

How does nematode protection work in corn seed treatment offerings?

VOTIVO® seed treatment has Bacillus firmus I-1582; a biological agent with activity as a nematode repellent. The following is a list of corn nematodes controlled or suppressed with VOTIVO® seed treatment offering:

 

What are my options for below-ground insect control if I do not use an insecticide seed treatment or an in-furrow insecticide?

There are no reach back insecticide treatments to control or suppress below-ground insects such as wireworm, white grub, seed corn maggot, or nematodes if a seed treatment such as Poncho®/VOTIVO® or an in-furrow insecticide treatment is not used at planting. Some farmers have been known to replant corn fields in early spring due to insect damage.

 

Conclusion

Modern agriculture has continued to develop the Egyptian concept of treating crop seeds. Statistics from 2014, reported 90% of corn seed was planted with seed treatment. Efforts to protect seed investments from soil pests and stressed growing conditions should be discussed with your seed brand representative.

Article Link

Sources:
1. Byamukama, E. and Strunk, C. 2019. Managing corn diseases with seed treatments. iGrow Corn Best Management Practices. Ch. 49. South Dakota State University Extension.
2. North, J.H., Gore, J., et. al. 2018. Value of neonicotinoid insecticide seed treatments in mid-south corn (Zea mays) production systems. Journal of Economic Entomology. Vol. 111. Pgs. 187-192.
3. Gullickson, G. 2022. Do seed treatments pay off? Successful Farming. https://www.agriculture.com/crops/ soybeans/a-seed-treatment-skirmish.
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. FOR CORN, EACH ACCELERON® SEED APPLIED SOLUTIONS OFFERING is a combination of separate individually registered products containing the active ingredients: BASIC plus Poncho®/VOTiVO® Offering for corn: metalaxyl, ethaboxam, prothioconazole, fluoxastrobin, clothianidin, Bacillus firmus I-1582. ELITE plus Poncho®/VOTiVO® Offering for corn: metalaxyl, ethaboxam, clothianidin, and Bacillus firmus I-1582; prothioconazole and fluoxastrobin at rates that suppress additional diseases. BASIC Offering for corn: metalaxyl, prothioconazole, fluoxastrobin, ethaboxam, and clothianidin. ELITE Offering for corn: metalaxyl, ethaboxam, and clothianidin; and prothioconazole and fluoxastrobin at rates that suppress additional diseases. BioRise® Corn Offering is the on-seed application of BioRise® 360 ST. BioRise® Corn Offering is included seamlessly across offerings on all class of 2017 and newer products. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Not all products are approved in all states. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. Poncho®, Poncho®/Votivo® and Votivo® are trademarks of BASF Corporation. Acceleron®, Bayer, Bayer Cross and BioRise® are trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1215_98201

 

Early Season Pests of Corn

 

Seed Pests

Pests that can feed on the seed are the seedcorn maggot, seedcorn beetle and slender seedcorn beetle, ants, and millipeds.

Seedcorn maggot

Seedcorn maggot larvae are yellowish white, about ¼-inch long and lack defined heads and legs. Larvae causes injury to the seed by burrowing into the kernel, thus resulting in reduced vigor and in some cases plant death (Figure 1). Fields with high organic matter, that have had animal manure applied or green manure from a cover crop that has been freshly incorporated are at higher risk, particularly in a wet, cool spring. A degree-day (DD) development models has been used to predict the timing of fly activity. Fifty percent of the overwintering generation emerges as adults after 371 DD (at 39 °F base) have accumulated based on the soil temperature in the top 2-inches of soil.


Figure 1. Seedcorn maggot. Image courtesy of Helene Doughty, Virginia Polytechnic Institute and State University, Bugwood.org.

 

Seedcorn beetles

Seedcorn beetles (seedcorn beetle and slender seedcorn beetle) occasionally attack corn seeds. The seedcorn beetle is a yellowish-brown beetle about 5/16 inch long with a patch of black in the middle of each wing cover. The slender seedcorn beetle is a shiny reddish-brown beetle about ¼-inch long, with a noticeable restriction between the thorax and the abdomen. The plant injury is more common when cold, wet weather delays the corn emergence. These beetles will feed on and consume the seed’s germ, resulting in “hollowed-out” seed. Injury will usually result in reduced plant stands. If the adult feeds on the mesocotyl it may result in plant stunting and eventually reduction in crop yield.

Millipedes

Millipedes range in body size from 1/4 to 1 1/4 inches and are dark brown to black, the body is rounded and have antenna and each body segment has two pairs of legs (Figure 2). This distinguishes them from wireworm larvae that they are sometimes confused with in the field. Millipedes are not insects but belong to a different class (arthropods) and usually not considered a significant pest of corn seeds. However, during cold wet springs, when seed germination is slowed and in fields with high plant residue or organic matter, injury can occur. This is particularly true when they can access the seed because the seed furrow did not completely close during planting. Seed treatments are not effective against millipedes.


Figure 2. Millipede. Image courtesy of Joseph Berger, Bugwood.org.

 

Red Imported fire ant

The red imported fire ant can attack the seed and injury can be extensive when populations are high within the field. In some areas of Texas, the injury can be extensive and most likely related to moisture and temperature. Injury is more common in fields that have been undisturbed or in no-till production systems. If the seed
is germinating it is more at risk and when planting conditions are not ideal, and the seed furrow does not collapse during planting allowing access to the seed, injury can be extensive. Particularly, under conditions that cause slow emergence.

 

Seed and Seedling Pests

Pests that can feed on the seed and seedling include, wireworm and southern corn rootworm.

Wireworm

Wireworm (there are many species) larvae are slender with only 6 legs and on the last abdominal segment an appendage that forms a “keyhole” type opening. Larva can range from ½ to 1-1/2 inches in length (Figure 3). There is soft- and hard-bodied wireworm species that range from pale white or shiny yellow to shiny brown in color. Wireworms are the larvae of click beetles. Click beetle females deposit eggs around the roots of grasses, which is why wireworms can be problematic in fields with a history of sod such as pasture or Conservation Reserve Program (CRP) fields. Wireworms may live in the soil for up to 6 or 7 years before pupating and emerging as adults. Injury tends to occur with early planted corn in conjunction with cold and wet conditions. Fields that are well drained are more likely to have infestations as compared to poorly drained fields. Larvae feed on the germ, resulting in similar “hollowed-out” seed injury of the seedcorn beetle complex. Wireworms will also feed on the underground portion of the root or stem of young corn plants by tunneling into them. Plants that survive will be stunted or wilted compared to surrounding plants. Once soils warm, wireworms will move deeper in the soil profile, reducing the injury potential.


Figure 3. Wireworms. Image courtesy of Frank Peairs, Colorado State University, Bugwood.org.

 

Southern corn

rootworm The southern corn rootworm is widely distributed and unlike the western and northern corn rootworm it feeds on a wide variety of crops as both an adult and larvae and can have several generations per year. The adults survive the winter in only the southern states and move northward during the growing season. The adult deposits eggs in the soil at the base of host plants, in corn it is only the first generation that is economically damaging. The larvae may attack the seed, in which injury can be confused with wireworm injury or tunnel into the mesocotyl killing the plant or severely stunting it. Interestingly, the Bt trait that controls the western and northern corn rootworm does not provide control for this species. Injury can be more severe when a legume cover crop is used. Termination of the cover crop less than 4 weeks prior to planting increases the risk. No-till cropping systems that utilize a cover crop are more at risk.

Seedling Pests

Those that are almost exclusive pests of the seedling include billbugs (many species but primarily maize billbug), chinch bugs, corn flea beetle, cutworms (many species), grape colaspis, slugs, southern corn leaf beetle, webworms (several species), and white grub (both true and annual species).

Billbug

There are several species of billbugs that can injure corn. The two major species are the southern corn billbug in the South and the maize billbug (Figure 4) in the Corn Belt. Adults usually only walk from overwintering sites to host plants, therefore, the injury that is done is usually localized to field borders. Nutsedge and corn are the predominant hosts for both species. Adults feed on the above portion of the plant and females oviposit in their feeding punctures and the developing larvae migrate down the stem. Occasionally, the female will deposit eggs in the soil and larvae will feed on the roots. When the growing point is injured, excessive tillering and plant stunting can occur and, in some cases, plant death.


Figure 4. Maize billbug. Image courtesy of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.

In the Atlantic Coastal Plain billbugs are a serious annual pest. Outside of this region the injury is more sporadic and often minor. Crop rotation and control of yellow nutsedge can help limit the potential for injury. Fields in continuous corn production in no-till systems are at higher risk of injury by billbugs.

Chinch bugs

Chinch bugs are small, roughly 1/6 inch, with a black body and white forewings that create a white ‘X’ on the abdomen (Figure 5). Newly hatched nymphs are bright red. Chinch bugs feed on the crowns and stems of corn plants and below ground on roots. Feeding damage from adults and nymphs causes reddish discoloration of leaves and stems.


Figure 5. Chinch bug adult. Image courtesy of Natalie Hummel, Louisiana State University AgCenter, Bugwood. org.

 

Corn flea beetle

The corn flea beetle is mostly a concern in the central and eastern US and causes little economic injury in the southern states. The adult overwinters in grassy areas and migrates to corn as it emerges, and temperatures allow insect activity (Figure 6). Large number of beetles can result in economic injury when the seedling stage is attacked. Harsh winter conditions can eliminate corn flea beetle adults and lower the risk of economic injury. This insect is a vector for Stewart’s wilt, a bacterial pathogen, that can infect susceptible corn products resulting in economic loss. Early planting timed to emergence of the adults can increase the risk of infestation, particularly when plant growth is slowed. Weedy fields may be at more of a risk.


Figure 6. Corn flea beetle adult. Photo courtesy of Frank Peairs, Colorado State University, Bugwood.org.

 

Cutworms

Cutworms are the larval stage of moths and there are several species that can attack corn Cutworms can vary in their feeding habit. The most economically important is the black cutworm. Black cutworm larvae feed below ground and sever corn plants from their roots near the soil line (Figure 7). Dingy cutworms climb the plant and consume leaf and stem tissue, while sandhill cutworms feed on the plant under-ground. Larval feeding can occur at the base of corn plants or underground, which results in wilted or completely clipped seedlings. The recommended injury threshold is when 5% of the plants are cut for those species which feed above ground.


Figure 7. Black cutworm. Image courtesy of Roger Schmidt, University of Wisconsin-Madison, Bugwood.org.

 

Grape colapsis

The grape colapsis is a sporadic pest mainly in the Central Corn Belt. Larvae resemble a very small white grub with a lightly curved, small white body with a tan head that are approximately 1/8-1/6 inch in length. Larvae overwinter in the soil and feed on the roots of the small seedlings, and several are usually found feeding on single plant. Feeding can limit water and nutrient uptake so damaged plants may appear wilted, stunted, or as if they have a nutrient deficiency from above the soil surface. Uprooting damaged plants will reveal the larvae. Because egg laying occurs in soybean, alfalfa, and other legumes, corn following a legume can be at higher risk. Injury can be more pronounced when seedling growth is slowed. There is not a recommend sampling program or economic threshold established for this pest, as well no rescue treatments in response to injury.

Slugs

Slugs can cause injury to corn seedlings by rasping the leaf tissue resulting in long vertical lines of dead tissue. In most cases, corn can out-grow the injury. Seed treatments are not effective for control of slugs. Injury is more common in no-till or reduced tillage fields and in springs followed by a mild winter.

Southern corn leaf beetle

The southern corn leaf beetle injury has become more common in the Corn Belt. The beetle is a small, <1/4 inch, dark beetle that is difficult to see as it blends in with the soil and readily drops to the ground when approached (Figure 8). The beetle feeds on the leaf margins and the stem. The damage can easily be mistaken as young cutworm or armyworm feeding. Stand reduction can occur, particularly while conditions are poor for rapid seedling growth.

The female deposits eggs at the base of the plants and larvae feed on the roots of corn during the early summer. Scouting for this pest can occur when scouting for cutworm injury, treatment is recommended when 25% infested/damage plants are found.


Figure 8. Southern corn leaf beetle. Image courtesy of University of Nebraska-Lincoln.

 

Sugarcane beetle

Sugarcane beetle is economically important in the Southeastern US and causes injury in the adult stage (Figure 9). The adults emerge from grassy field margins or pasture and migrate to corn fields to feed on newly emerged plants. The feed below the soil line and chew through the mesocotyl. The injury results in killed seedlings or stunted if feeding occurs on larger plants. A single adult can injure several plants and the resulting stand loss can result in yield losses. However, the injury is often sporadic, isolated, and unpredictable. Fields at the highest risk border grassy areas.


Figure 9. Sugarcane beetle. Image courtesy of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.

 

Sod webworms

There are several species of sod webworms, but the two most common that may attack corn are the corn root webworm and the bluegrass webworm. The larvae are off-white with numerous small black spots with numerous pale hairs. Webworms are very active and will move vigorously when handled. These are occasional pests in early corn. Plants in relatively small areas can be killed by sod webworm caterpillars during late May and early June. Damage usually occurs more severe when corn follows sod, and injury is scattered throughout the field. Under severe infestations, up to 75% of the plants from an infested areas may be injured. Injury occurs near ground level that can result in plants that are cut off and partially dragged tunnels made by larvae. This type of injury is very similar to that caused by cutworms, especially the black cutworm; however, webworms usually consume more of the plant.

White grubs

White grubs are occasional pests of corn seedlings. Annual white grubs (ex: Japanese beetle) have a one-year life cycle with the grub stage from late July through mid-June the following year. True white grubs (ex: May and June beetles) have a two to three-year life cycle with the grub stage from August through the next year and sometimes during portions of the third year (Figure 10). Annual grubs tend to be more sporadic and rarely result in economic injury to corn. The true white grub is more wide-spread and usually a more common pest of corn. White grub damage typically appears as stunted, wilted, discolored, or dead seedlings and/or as gaps in rows where plants fail to emerge. White grubs prune roots and can feed on the mesocotyl causing plant death. Injury is usually more severe when corn follows sod or pasture.

Additionally, field surrounded by trees, (popular, cottonwood, willow and ash) are attractive to the adults that feed on the leaves, with females then laying eggs in the soil near the trees. Therefore, 2 years after high numbers of adults are noticed feeding on leaves, the risk of injury by 2nd instar larvae is the highest. There are no rescue treatments labeled for white grub infestations. Preventative measures should be taken before planting if scouting reveals a presence of true white grubs in a field.


Figure 10. True white grub. Image courtesy of Alton N. Sparks, Jr., University of Georgia, Bugwood.org.

 

Management Tactics

There are several management practices that can help reduce early season corn insect damage (Table 1). Crop rotation with a non-grass crop, conventional tillage, and timely planting in good soil conditions can help reduce corn seedling stress and align timing of corn insect susceptibility with lower insect pressure. With the subterranean pests, there are no responsive management tactics available so the reliance on preventative tactics is the only management strategy. Insecticide rescue treatments are available for some insects; however, timing is critical, which makes preventative treatments beneficial and necessary for some insect species. Insecticidal seed treatments can help to control several early season insects for up to 30 days after planting. Insecticide seed treatment products, such as clothianidin, can help reduce damage caused by secondary pests including: seedcorn maggot, white grub, wireworm, black cutworm, Japanese beetle larva, and chinch bug.

Article Link

Sources
1North, J.H. et. al. 2018. Value of neonicotinoid insecticide seed treatments in mid-south corn (Zea mays) production systems. Journal of Economic Entomology. Volume 111. pp. 187–192. https://www.researchgate. net/profile/John_North4/publication/321336086_Value_of_Neonicotinoid_Insecticide_Seed_Treatments_
in_Mid-South_Corn_Zea_mays_Production_Systems/links/5aecb687aca2727bc004ee2b/Value-of-Neonicotinoid-Insecticide-Seed-Treatments-in-Mid-South-Corn-Zea-mays-Production-Systems.pdf
Reisig, D. 2015. Scouting for Seedling Insects. North Carolina State University Extension. https://entomology. ces.ncsu.edu/field-corn-insects/scouting-and-thresholds/scouting-for-seedling-insects/
Reisig, D. 2018. Are Insecticidal Seed Treatments and In-Furrow Insecticides Worth It in Corn? North Carolina State University Extension. https://entomology.ces.ncsu.edu/2018/04/are-insecticidal-seed-treatments-and-in-furrow-insecticides-worth-it-in-corn/
Sappington, T., Hesler, L. Allen, C., Luttrell, R. and Papiernik, S. 2018. Prevalence of Sporadic Insect Pests of Seedling Corn and Factors Affecting Risk of Infestation. Journal of Integrated Pest Management. Volume 9. https://academic.oup.com/jipm/article/9/1/16/5033787
Legal Statement
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
Tank mixtures: The applicable labeling for each product must be in the possession of the user at the time of application. Follow applicable use instructions, including application rates, precautions and restrictions of each product used in the tank mixture. Not all tank mix product formulations have been tested for compatibility or performance other than specifically listed by brand name. Always predetermine the compatibility of tank mixtures by mixing small proportional quantities in advance. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1215_60951