Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Soybean
Check stands on all April-planted soybeans now. Rain is feast or famine this year, and right now, rain, soil moisture, and cool temperatures have combined to cause major problems in soybean fields planted within the last two weeks. Gray garden slug eggs have hatched recently, causing a very large increase in slug populations. In one field we visited, soybeans were largely up and out of the ground and expanding unifoliates before last weekend’s rain came in. I am optimistic that those soybeans will outrun major damage. Soybeans that were just starting to crack might not be so fortunate, and now that eggs have hatched, slugs are going to be increasing in size as we start planting into wet soil. Close your seed slots. Use row cleaners to move residue out of the way. If using any sort of tillage, be sure to have an insecticidal seed treatment on the beans, because cool wet weather combined with tillage sets fields up for seedcorn maggot damage. Reports came in at the end of this week, and more will come in next week of seedcorn maggot damage to soybean stands. Soybean affected by SCM will be stunted, growing slower than healthy plants, the stems below ground will be swollen and off-color. The center portion of the vascular system will turn brown. As damage progresses, plants will wilt and collapse. There are no rescue treatments for SCM. If you see SCM damage, wait a week or so to assess plant stand, this should give weak plants enough time to fall out of the stand, giving you the ability to make a better stand assessment. Narrower row soybean under irrigated conditions and with a branching habit can compensate for a surprising amount of stand loss, down to as few as 70 thousand plants.

Seedcorn maggot damage to soybean

Corn
Cutworm injury reports are coming in, along with reports of bird damage. Cutworm tend to make burrows scattered around the fields and may drag plants into burrows. Birds tend more to pluck plants out, leaving holes at the base of plants and may pull up below ground portions of the plant. We had a major flight of black cutworm at the beginning of April in the northern half of the state. Those cutworm larvae may be large enough to begin cutting plants this week. Pay attention to weedy fields, fields with late terminated cover crop, and late planted fields. Another pest that will be hiding in small grain cover crops at this point is brown stink bug. Fields planted into green or late terminated rye, wheat, or barley are at greater risk for stink bug damage. Treat if you find more than 13 stink bugs on or at the base of 100 plants.

Small Grain
Scout for armyworm activity, particularly in the northern part of the state. Examine first the debris and undergrowth on the ground surface along field margins and lodged areas. Check for small armyworms curled in a C-shape at the base of plants or under debris and weeds. Examine 5 linear foot of row in at least 10 locations throughout a field, count the worms and note any leaf defoliation and/or head clipping. Armyworm frass or droppings also may be found on the soil surface. As a general rule, barley should be treated if the number of armyworms exceeds one per linear foot between rows. In wheat, armyworms tend to nibble on the tips of kernels rather than clip heads; thus, populations of one to two worms per linear foot between rows are required to justify control. In high management wheat fields, treatment is recommended when armyworm levels exceed 3 to 5 per square foot of surface area.

Early Season Moth Activity
Many thanks to Haley Sater with UMD Cooperative Extension and Joanne Whalen, Extension entomologist emeritus extraordinaire for assistance with checking traps.