David Owens, Extension Entomologist, owensd@udel.edu
Seedcorn Maggot
Overwintering seedcorn maggot adults are active now. Fields that have incorporated organic matter (cover crop, heavy residue, and especially poultry manure) are the most attractive to flies for oviposition. If planting in such a field within 3 weeks, be sure to have an insecticidal seed treatment. Diazinon is also labeled for some crops for other early season stand reducers such as wireworm and cutworm. It can also give excellent seedcorn maggot control. It needs to be incorporated into the soil prior to planting. Seeds planted deeper will also have a greater likelihood of sustaining heavier damage than seed planted at a shallower depth. We want seed to emerge and grow as quickly as possible.
Alliums
Allium leafminer should be active now. Scout for oviposition scars on the leaves. They will appear as a row of round circular lesions. Good control options include row covers for March and April and systemic insecticides used with a spreader type adjuvant. If you plan to use row covers, you might want to make an insecticide application first and then cover immediately after. Scorpion, Exirel, Radiant, and Entrust (OMRI) are the most effective materials, are translaminar or systemic, and will have the longest residual activity. Repeat applications a couple of times during the adult flight period which typically lasts 5-6 weeks. Pyrethroids should be applied more frequently.