2014 University of Minnesota Cooperative Black Cutworm Trapping Network

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1 2014 University of Minnesota Cooperative Black Cutworm Trapping Network Report # 7 Week of May 17- May 23, 2014 For more information and daily trap capture values: work/index.htm Issue #2) Migration patterns, # 3) Cutworm species and what makes a field at risk, #4)Predicting cutworm development with degree days, #5)Scouting for black cutworm and thresholds. May 29, 2014 There is still activity but much less than last week. Steele County had 11 moths on 5/19. This has been a very active trap. I'd be looking hard at susceptible crops and fields for scouting. Black cutworm cutting forecast Pay close attention to any leaf feeding as you scout. There are at least two flights, April 28 and May 8 (Table 1), where larvae would be large enough show leaf feeding (Table 2) and may be large enough to cut corn in warmer locations Table 3. The highest, but not exclusive, risk for black cutworm infestations is highest from Faribault and Steele County in SC MN and northwest up the Minnesota River to southern WC MN. The late April flight detected in Lac Qui Parle and Faribault counties could lead to cutting stage cutworms attacking small corn. In addition to the black cutworm larvae found in my Brown county yard, I just received a report of black cutworm leaf feeding on corn near the Sibley/Renville County line (Curt Burns). Fields along the diagonal from Faribault to Lac Qui Parle are at some risk from the April 28, flight. The 5/12-5/14 period was the most active of the season with Murray, Lyon, Redwood, Sibley and Freeborn having multiple captures/night but less than eight in a two night period. The 5/08/2014 flight detected by the Swift County trap seems more localized with the bulk of that system north and west.

2 Table 1. County Dates Faribault 4/28 5/13-5/14 Lac Qui Parle 4/28-4/29 Murray 5/10-5/11 Steele 5/11-5/12, 5/19-20 Swift 5/07-5/08 Look at the tubercles on the cutworm picture below; the small black bumps on each segment near the back of the cutworm. The unequal size is a characteristic of black cutworms. The overall appearance of black cutworm larvae is black and "greasy". Under a good hand lens, the skin of the black cutworm has a granular appearance.

3 Table 2. Cumulative Black Black Degree Cutworm Cutworm Days Stage Activity 0 (Biofix) Significant Moth Capture Egg laying 90 Egg hatch st-3rd instar Leaf feeding th instar Cutting begins th instar Cutting begins th instar Cutting slows Pupa No feeding Black cutworm larvae smaller than 3rd instar are very difficult to find. Look for the larvae under clods and crop residue. They can usually be found at the boundary of wet and dry soil. Leaf feeding is usually the first sign of black cutworm injury to corn. Look for injury to weeds in addition to the crop. Corn less than 4 leaf stage is most susceptible to cutting. However, late instar cutworms can still kill up to 6 leaf corn by burrowing into the growing point. Sugarbeets and other dicot crops have their growing point above ground at emergence and are at greater risk from death from cutworm cutting. Table 3. Growing Degree Day Summary through May 27, 2014 Base 50/86 Flight Flight Flight Flight 4/28/2014 5/8/2014 5/12/2014 5/19/2014 departure from Location total normal total total total Crookston Moorhead Alexandria Montevideo Morris Wheaton Becker Collegeville Melrose Olivia St. Cloud Willmar Forest Lake MSP Airport Mora St. Paul - UofM Lamberton

4 Marshall Redwood Falls Sioux Falls North Mankato Owatonna Waseca Winnebago La Crosse Preston Red Wing Rochester Rosemount How to prioritize fields for cutworm scouting You can't scout everything at once. While I can't guarantee all cutworms will follow the rules, the following tips might help you schedule your effort. 1) Fields that are worked and planted late are at higher risk for egg laying by immigrating black cutworm moths. Un-worked soybean stubble may be somewhat more attractive than corn. Early moth flights and late planted corn lead to higher risk for cutting corn. Soybean ground tends to warm earlier in the spring leading to point 2. 2) Fields with early season weed growth are at higher risk from egg laying. Winter annuals and early emerging spring annuals are attractive areas for female black cutworms to lay eggs. Common lambsquarters seem to be a favorite. Tillage removes weeds and the field becomes less attractive for egg laying. Pay close attention to areas that had weed pressure when scouting. 3) Fields where thunderstorms moved through prior to tillage. The significant captures (Table 1.) shows when we have had flights into MN. 4) Fields with low lying areas and windbreaks tend to concentrate moths dropping out of thunderstorms. How to prioritize corn hybrids for cutworm scouting Nothing is guaranteed and the following are not guaranteed when large cutworms attack small corn. However, you can assign higher risk to some varieties. 1) Non-Bt hybrids and Bt hybrids without the Herculex I or Viptera above ground traits are not protected against black cutworm.

5 2) Fields with a corn rootworm insecticide labeled for cutworm have some protection from attack. Neonicitinoid seed treatments (Poncho, Cruiser, Gaucho) can provide some protection, particularly at higher rates but they can be overwhelmed. If you are unsure, seed suppliers can provide the information on the cutworm protection of the seed you planted. Don't Overreact Labeled rescue foliar insecticides work well and localized cutworm infestations can be spot treated. However, Before you treat: Make sure cutworms are the cause of your injured or missing corn. Make sure cutworms are still present! Cutworms need to eat Bt to be affective. Some leaf feeding can be expected on Herculex, Smart Stax and Viptera hybrids before they are affective. Neonicitinoid seed insecticides are similar. There is little benefit to spraying dead or pupated cutworms. Always read and follow the pesticide label Products are mentioned for illustrative purposes only. Their inclusion does not mean endorsement and their absence does not imply disapproval. Good luck, Bruce Potter Travis Vollmer Extension IPM Specialist SW MN Research Plot Technician University of Minnesota University of Minnesota Southwest Research and Outreach Center Southwest Research and Outreach Center th Street Lamberton, MN Phone: Cell: Fax: bpotter@umn.edu 2014, Regents of the University of Minnesota. All rights reserved. The University of Minnesota Extension is an equal opportunity educator and employer.