Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Early Season Moth Activity

Many thanks to Joanne Whalen for assisting with trapping efforts. Moth captures are beginning to decline but be sure to start scouting small grains for armyworm activity.

 

Location # of Nights Total Catch
TAW BCW
Willards, MD 6 5 8
Laurel, DE
Seaford, DE 6 2 9
Sudlersville, MD 7 0 55
Harrington, DE 6 71 30
Smyrna, DE 6 132 43
Middletown, DE 13 148 48

 

Corn

Now that corn is up, begin scouting for cutworm injury, especially in fields with a short period of time between cover crop termination and plant emergence. Initial injury generally appears as a row of circular holes across the leaf blade. Look at 10 plants in 10 locations per field and consider a treatment if 10% show cutworm feeding. Cutworm injury can be confused with stink bug injury, but stink bugs will leave very ragged holes, not circular holes. Some of the Bt traits in corn do a great job preventing cutworm injury from progressing, so you may also want to continue watching a field that has plants with small holes in leaves to see if it progresses to actual cut plants before pulling a trigger on a spray. The handy Bt trait table can be found here: https://agrilife.org/lubbock/files/2022/02/BtTraitTable-March2022.pdf

You may also begin seeing signs of wireworm injury in fields. Wireworm injury will appear either as a portion of a leaf blade with a bright yellow streak or as a dead whorl leaf. There are no rescue treatments for wireworm, but if you see damage, it may be useful to dig 12x12x6 holes to determine what the population is in the field for future decision making.

Finally, in no-till corn, be sure to scout for slug injury. The next week looks very favorable for slugs. Damage is most severe prior to V3. There are no established thresholds for slugs, although Penn State suggests a threshold of 1 slug per square foot. I have heard rumor that the price of Deadline is higher this year, which if so, could warrant a bit more of a wait-and see approach. Other options include cultivation and application of a 30% urea solution at night on a humid, still night when slugs are active on the surface, minimum 10 gallons per acre broadcast. Soil cultivation or tillage will also decrease slug activity.

Soybean

Our two most damaging early season invertebrate pests should be very active this week: slugs and seedcorn maggot. Soybeans planted into thick cover crop or high residue environments without turbo tillage or vertical tillage need to be scouted carefully for signs of stand loss. Rescue treatments are very difficult if not impossible to time once plants are emerging out of the soil.

The other important pest, seedcorn maggot, is, unlike slugs, favored by tillage. Organic matter incorporation, and especially manure or a legume cover crop such as crimson clover or vetch, is highly attractive to flies. We planted our second seedcorn maggot seed treatment trial in Georgetown this week, basing our timing off of a degree day model of 1,080 degree days with a base temperature of 39. Adult flies will continue to be active for the next two weeks or so. An insecticidal seed treatment may be warranted for soybean planted in these high risk scenarios.

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