Agronomic Crop Insect Scouting

David Owens, Extension Entomologist;

Armyworm and Cutworm Trap Counts
Cutworm adult counts have risen a bit since last week in several locations. I expect they will continue to rise, especially after storm fronts last Sunday and forecast for today. These storms literally rain moths. Trap counts are as follows:

Trap Location True Armyworm per night Black Cutworm per night
Willards, MD 0.1 0.7
Salisbury, MD 0.1 0.7
Laurel, DE 0.9 2.7
Seaford, DE 7.4 7.0
Bridgeville, DE 4.9 1.7
Harrington, DE 0.9 1.0
Wilson (6) 10.2 5.2
Owls Nest (6) 3.8 0.5
Thompson (6) 0.2 0.5
Sudlersville, MD 0 0.1

Insecticides are sometimes put in a herbicide burn down spray, usually with the intended target being black cutworm. Bt corn almost always comes with a neonic seed treatment, either Cruiser or Poncho. Both the traits and seed treatments will provide some protection vs small cutworm larvae. Larger larvae that cut plants are not going to be controlled by either. When might we see larger larvae? If a burndown spray is going out less than 1-2 weeks before planting, there is a possibility that cutworms are hiding in the cover and will not starve before the corn is up.

Scouting for rescue applications can be timed based on degree days. It takes up to 300 degree days (base 50) between an intense moth flight and larvae to reach a size where they begin cutting plants. The definition of an intense moth flight varies depending on the style of trap being used, but conservatively, we can use April 11 as a biofix date to begin accumulating degree days in DE. If we expect corn to emerge after 300 degree days, and corn is being planted into a cover crop within 1-2 weeks of termination, there is the possibility that large damaging larvae can be present. Severe infestations of cutworms are, however, infrequent.

There is a potential drawback to insecticide use at burndown: slugs. Survey work from Virginia in 2018 found a strong correlation between slug injury and early insecticide use. Pyrethroids will eliminate ground beetles that feed on slugs, but the insecticide will not touch the slug. If your field has had a history of slug issues, you may want to consider leaving the pyrethroid out to give beneficials a chance to work on the slugs.

Small Grains
According to degree day models, we are at peak cereal leaf beetle egg lay right now. CLB is very quiet, few adults and even fewer eggs have been observed in fields across the state. Our next pests to be scouting for are sawfly and armyworm.

Aphid pressure in the last two weeks has increased in many fields. Although wasp activity is increasing, there are fields with well over 150 aphids per foot. In high pressure fields, honeydew is obvious, parasitoid activity is low. If heads are peaking out, pay attention to English Grain movement onto the head. Bird Cherry Oat Aphid is also present, it prefers the bottom half of the plant and can build up to numbers just as high as the EGA in the upper canopy/head. If you are planning a flagleaf spray, it may be worthwhile in some of these fields to include a pyrethroid. Having said that, there is not much data to indicate what, if any, yield response may result.