Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Alfalfa weevil continue to be active in other parts of the region. This past week, Dr. Kelly Hamby was able to capture a large number from alfalfa plots at Beltsville. Recent spray trial data from a population in MD indicates that dimethoate efficacy on weevils is limited. A report of very high aphid activity came in this week from a field that was treated with a pyrethroid for alfalfa weevil two weeks ago. Suggested thresholds are 50 aphids per sweep. In the absence of beneficial insects such as ladybugs, syrphid maggots, or parasitoid wasps, an early harvest is generally advisable.

We are at our cereal leaf beetle degree day target for eggs. Two years ago, when we were looking, 182 degree days (base 8C) was around the first observation of eggs. So far, this insect has been very quiet. Right now, moth flights are very low in most of Delaware (but see this weeks moth counts), and I anticipate that generally the pest population is low enough not to need a blanket pyrethroid tank mix with a head spray fungicide. Having said that, we do not know how wide of an area a trap capture is indicative of a pest population, and our trap near Smyrna has been capturing high numbers of armyworm moths.

Seedcorn Maggot
First generation seedcorn maggot flies peak emergence will be occurring this week coming. This next flight is usually the last one to potentially cause significant injury. I am starting to see flies again in my maggot field, with many pupae still developing. Fields at risk will have just had a cover crop or manure tilled into the soil. In such fields, use of a seed treatment is strongly advised.