Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Timothy

A report came in this week of very high aphid numbers in timothy following a pyrethroid application. There are several aphid species that will get into grass forage, but the most damaging species is greenbug. Greenbug injects a toxic saliva that will cause the plant to yellow and be stunted. Other labeled insecticides in grass hay besides pyrethroids are Malathion and Sefina. Sefina is a newer insecticide that is aphid specific, very low use rate, and has a 0 day PHI. If looking for its label, be aware that grass forage crops appear as a supplemental label and not on the primary label. If you try to access the label through CDMS, you will need to scroll through the list of 2ee and supplemental labels to find it.

Small Grains

If wheat or barley did not receive an insecticide with a head-stage fungicide, scout it now for cereal leaf beetle and for true armyworm. True armyworm thresholds are 2 per row foot (or 3-5 per square foot) in wheat and 1 per row feet in barley. They are most active at night and will hide under soil residue during the day. If you do choose to spray your small grains, keep in mind most of the pyrethroids have a very long pre harvest interval.

Corn

Cutworms are large enough now to cut plants. Look for wilted leaves on the soil surface or partially dragged into the soil. If an insecticide was used in the furrow, do some digging before thinking about a follow up spray. In one such field I visited this week, two thirds of the cutworms were dead or dying. Varieites with the Cry1F toxin will control cutworms; you can find the trait packages with Cry1F in them here: https://agrilife.org/lubbock/files/2021/02/BtTraitTable_Feb_2021B.pdf. Thresholds are 3% plants cut on 1-2 leaf stage corn. The only labeled products are pyrethroids.

Soybeans

Several reports came in this week of seedcorn maggot damage to soybeans. Affected plants will have scarring on the cotyledons, wilting plants, wilting cotyledons following complete stem severance at the ground, swollen below ground stem tissue and holes with a shredded looing appearance. Affected plants sometimes recover but may also be permanently stunted. Careful stand assessment is called for; there are no rescue treatments for seedcorn maggot. With warming soils, the likelihood of a second round of seedcorn maggot damage decreases considerably should a replant be necessary.

Continue scouting carefully for slugs. Despite the warmth and sunshine, we have adequate soil moisture for slugs to remain active. Be sure to scout carefully where seed slots are open. Slug feeding on the cotyledon is different from seedcorn maggot in that it looks more like a regular gouge, almost as if someone tried to take a pencil through it.

Bean leaf beetles are now active in soybean.

Early Season Moth Trapping

Many thanks to Joanne Whalen and to the farmers that permitted us to put taps on their land this spring. This is the final armyworm and cutworm trapping update. Armyworm continues to remain somewhat elevated in the Smyrna area.