Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Early Season Moth Activity
Many thanks to Haley Sater with UMD Cooperative Extension and Joanne Whalen, Extension entomologist emeritus extraordinaire for assistance with checking traps.

For the third year in a row, Smyrna traps are catching extremely high numbers of true armyworm. This may be a landscape quirk or indicative of greater pest pressure in the northern Kent/southern New Castle County area, especially along the coast. Black cutworm trap counts are also extremely high in Smyrna, more so than the last several years of trapping. Cutworm numbers also came up in Seaford and Harrington, but so far are in line with this time last year.

Given the unusually high activity in one trap, I highly recommend cover crop and weeds be terminated well in advance of planting. Both species can cause significant damage to corn. True armyworm prefers to lay eggs in grasses while black cutworm is much less choosy. Neonicotinoid seed treatments are not effective on either species, and only a few of the Bt trait packages are. Early larval feeding often appears as small, circular holes in leaves (often paired and symmetrical).

Alfalfa
Continue scouting alfalfa. Many fields were sprayed within the last two weeks for alfalfa weevil. Weevil activity began more than 3 weeks earlier than usual this year, but larvae have grown slowly until most recently. Because of several cold spells, larvae might not have come into contact with an adequate amount of insecticide residue before it degraded, thus it is possible that product efficacy targeting these early, small larvae may not have been as great as expected. Adults are active and laying eggs, thus we also get a continuing ‘trickle’ of new larvae in fields. Third, many of the fields that we scouted had populations many times above threshold. Given these three factors, products that ordinarily would achieve high rates of control might not bring the larval population down enough to be under a treatment threshold. Recent spray trial work continues to show Steward has the greatest weevil activity, followed by Warrior II and tank mixes of pyrethroid + dimethoate. Combinations that have not been tested and will be next season include pyrethroid + Lannate and pyrethroid + Imidan. We tested Carbaryl two years ago and it was about equivalent to a pyrethroid but had shorter residual activity.

With the current crop and insect conditions, follow-up scouting is extremely important.

Morgan Malone and I filmed a video discussing alfalfa weevil management and is posted to UD Cooperative Extension’s YouTube page. Many thanks to Michele Walfred for editing assistance. You can find it here: https://www.youtube.com/watch?v=HY6RPjC8oE0&t=7s

Corn and Soybean
In addition to the elevated moth counts observed in the Smyrna area, gray garden slug eggs have hatched, courtesy of an unusually warm February. This is considerably earlier than usual. Dry weather, soil disturbance, moving residue out of the way, and ensuring seed gets into the ground will all help reduce the likelihood of significant damage from slugs.

Small Grains
A report came in earlier this week of elevated aphid activity in a malting barley field. Fortunately, natural enemies were present and they may be able to hold aphids back until a flag leaf fungicide or scab fungicide application. Several fields are exhibiting signs of root pathogen and barley yellow dwarf virus, even in fields that had low aphid counts up until February. At this point in the season, any continued virus transmission is unlikely to cause significant damage. Cereal leaf beetle, if you can find it, should be laying eggs now. Pyrethroids are very effective on all small grain pests, but pay attention to the long PHI’s of some of them, especially once we move into May.