Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Many thanks to Joanne Whalen for assisting with trapping efforts. Somewhat moderately high populations of true armyworm continue to be detected in the Harrington and Smyrna area while remaining traps have quite low populations.


Location # of Nights Total Catch
Laurel, DE 9 1
Seaford, DE 9 5 11
Sudlersville, MD 7 0 4
Harrington, DE 8 34 86
Smyrna, DE 8 130 19
Middletown, DE 8 53 69



Continue to scout for alfalfa weevil. We saw numerous weevil feeding and oviposition scars in samples collected two weeks ago. Most of the early weevil larvae are now pupating, but we may have another round of larvae soon. Most alfalfa should have flower buds by now, meaning that rather than treat an above threshold alfalfa weevil population, early harvest is a viable management tactic.

Corn and Soybean

There are reports of damage to early planted soybean caused by seedcorn maggot and by slugs. Recent cool, wet weather is favorable to both. Seedcorn maggot is attracted to fields with cover crop or manure tilled in and incorporated into the soil. Soybean might fail to emerge. Plants that do emerge may wilt or remain stunted because of the compromised root system. Cotyledons will have small pin holes and etchings, the roots will be brown and the stem will have a shredded appearance. Unfortunately, there is nothing that can be done after planting. Soybean treated with an insecticidal seed treatment (which can be found at the end of the UD soybean insect pest management publication: can help reduce seedcorn maggot damage, but with weather conditions such as we have had and if a field is highly attractive to flies, seed treatments can be overwhelmed. Corn is able to withstand greater injury as the maggots often feed on the senescing kernel rather than the root or stem, but can still be stunted. If a stand is damaged by seedcorn maggot, assess stand carefully and discuss with your local agronomist or extension agronomist Jarrod Miller or our new farm business specialist Nate Bruce to determine understand the cost, implications and justifiability of replanting or overplanting.

This past week, reports have also come in of slug damaged stands in no-till soybean fields. A large number of slug eggs have been hatching this past week, especially in fields with heavy crop residue or thick cover crop. If planting into these conditions, make sure the seed gets into the ground first and foremost. If scouting fields prior to planting, be aware that there are no established thresholds for soybean. If a field averages greater than 1-2 slugs per square foot, it is at a higher risk. Anything that encourages rapid seedling growth will help reduce slug damage. Row cleaners can help to push residue off the furrow so the ground warms faster, and delaying planting until the soil warms can also help. Slug baits can also help reduce slug damage. Slug bait is most effective in soybean if applied before or just as soybean begins emerging, following rain but followed by warm, dry weather so that intoxicated slugs dry out in the sun.

Later this week coming up, we will have accumulated enough growing degree days for cutworms to be large enough to cut corn plants. We had an early cutworm flight in Kent County in April. This does not mean that a given field will have cutworm injury, and in corn, some of the Bt traits are especially suited to reduce cutworm injury. If planting under late terminated conditions or planted green, be aware that additional scouting is warranted. Look for plants with rows of circular holes or cut plants.

Small Grains

Continue to scout for armyworm activity in small grains, especially in the Harrington and Smyrna areas where traps intercepted large numbers of moths earlier this season, and especially fields that did not have an insecticide tank mixed with a fungicide application. Be mindful also of the long pre harvest intervals of all pyrethroids except for Mustang. Armyworm threshold is 2 per row foot. In the last few years, we have not had an above threshold population of armyworm.

Spotted Lanternfly

Spotted lanternfly eggs are hatching. Be on the alert when moving equipment or plants out of the quarantine areas. Early instar nymphs are black with white spots.