Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Early Season Moth Activity
Many thanks to Joanne Whalen and David Armentrout at UMD for assistance with monitoring pheromone traps. Moth activity continues to remain low; I do not anticipate major issues with armyworm in small grain or early pasture at this time.

Location # of Nights Total Catch
Salisbury, MD 7 0 6
Seaford, DE 5 0 8
Sudlersville, MD 7 0 13
Harrington, DE 5  —  —
Smyrna, DE 7 1 0
Middletown, DE 14 0 0

Corn and Soybean
Any soybean that has gone in the ground in the last week is at higher risk for slugs and a moderate risk for seedcorn maggot due to cooler, cloudy conditions and recent rainfall. Be sure to scout beans carefully and often as they are expected to emerge so that if a slug rescue treatment is deemed necessary, it is done timely. That can be a challenge with soybean. Make sure seed slots are closed. If open, look at the condition of the seed and cotyledon, they may be fed upon before they emerge. For corn, the risk of injury is greatest when the plants have 3 leaves or less, there is active feeding on the whorl leaf that has not fully unfurled, and the plants appear to be ‘going backwards’. They may do that this week in problem fields given several bouts of rain in the forecast and overcast, cool days.

As a caveat, for both corn and soybean, the relationship between slug feeding and yield is murkier. If whorl leaves are not being fed upon and the weather conditions are warm and dry, corn can recover. Soybeans can compensate for considerable stand loss provided the stand is more or less even. A stand of 70 thousand plants per acre, especially with irrigation, can yield up to 95% of original stand target, or if there are heavily damaged areas, fill-in replanting may be necessary as opposed to the entire field.

Rescue treatments are limited to granular baits: metaldehyde such as Deadline or iron phosphate such as Ferrox AQ. There are others on the market and this is not meant to be an endorsement. Check labels and your state’s department of agriculture for state registration availability. Applying them can be a challenge, it can be applied by plane or by spreader. In small pot trials I use a little hand spreader which is obviously not feasible on more than a half acre or so.

If scouting a just planted field, sift through ground residue. A field with 2 or more slugs per square foot should be monitored carefully.

Opposite of slugs are seedcorn maggot, which is attracted to tilled fields with organic matter incorporation, whether that be manure, crop residue or cover crop. There are no rescue treatments for SCM, but it can be preventatively manged with an insecticide seed treatment. If an insecticide seed treatment was not used, and the field worked, scout plants about a week after emergence for signs of seedcorn maggot damage to plants and seed. On the cotyledon it will appear as black etching. Seedlings will wilt in place and the stems will be hollowed.