David Owens, Extension Entomologist, owensd@udel.edu
Alfalfa
Begin scouting regrowth for potato leaf hopper, which typically appears towards the end of May. Stubble treatments are rarely necessary, as cut alfalfa stimulates adults to seek ‘greener pasture.’ Resistant varieties have glandular trichomes that glue nymphs down and trap them; these varieties may have as much as 75% fewer leafhopper than non-resistant varieties. There are also non-yellowing varieties which still need to be scouted for as they will suffer leafhopper damage even without the visual after-the-fact symptoms.
Field Corn
Continue scouting for cutworm damage to corn. We have now accumulated degree days to where black cutworm larvae, if present, are large enough to cut plants.
Soybean
In the past few days, reports of seedcorn maggot damage have come in on early planted soybean. Affected plant stems have a shredded appearance internally from where maggots have been feeding. Cotyledons may also have small holes and pathways etched into them that look similar to, but smaller than, slug feeding. Seedcorn maggot is favored by cool conditions and recent tillage incorporating crop residue or manure. Unfortunately, there are no rescue treatments. Even neonicotinoid seed treatments may not provide adequate stand protection in situations in which a large number of flies migrate into a field to lay eggs. The best thing to do is to do stand counts and discuss with your county agent as to whether or not the damage would justify replanting. The first two generations of seedcorn maggot are the most damaging. The second generation is passing, meaning that beans should not face seedcorn maggot again this year.