Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

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. Moth counts were fairly low this week, possibly as a result of cooler night temperatures.

Location # of Nights Total Catch
Salisbury, MD 7 2 1
Seaford, DE 7 0 0
Sudlersville, MD 7 0 8
Harrington, DE 7 64 8
Smyrna, DE 7 138 55
Middletown, DE 7 6


Early season insect pest injury is beginning to reveal itself. This week there were reports of cutworm and seedcorn maggot, and wireworm/white grub damage will also be evident. With cool weather and rain, we are entering a period of higher risk for slug damage. Young corn is at the greatest risk for heavy feeding damage. If the plants and the stand appear to be going ‘backwards’, multiple slugs are present under residue near the plants, and the forecast indicates cool weather which reduces crop growth, a treatment might be advised. Deadline MPs at 10 pounds per acre has given us great slug reduction in previous experiments. Ferroxx AQ is an iron phosphate bait that is safer for vertebrates and can be as effective as Deadline. It has a label rate of 4-25 pounds per acre. Slug baits work best if a couple of days of dry weather occur after application.

A report came in this week of cutworm activity in field corn. There are a couple of different groups of cutworm. Some species like Dingy and Clay Backed overwinter as larvae and can be present at planting. The field we visited had large caterpillars, large open circular tunnels, and, most importantly, corn that was not quite yet at V2. These plants will recover from cutworm feeding. Large cutworms are difficult to kill and these cutworms were about ready to cycle out of the field. On the other hand, Black cutworm moths are laying eggs now, and are attracted to weedy fields. Our first significant flight occurred about 3 weeks ago as indicated by our Smyrna and Middletown pheromone traps. By the end of next week, the first black cutworms should be large enough to cut plants. Pay attention to weedy fields and fields that had cover crop terminated late, close to or even after planting. Black cutworm hides during the day in tunnels and will cut plants and drag the cut plant into its burrow to feed. If a field is above threshold and cutworms are present, a pyrethroid application is recommended.

Seedcorn maggot damage can be a bit more subtle, resulting in withered plants or, more often, stunted plants. Wireworm damage will appear either as withered plants with a small hole underground or plants with yellow streaks. There are no rescue treatments for either.

Last year, we made a short video showing some of the early season pest damage on corn. You can check it out at

Pay urgent attention to emerging soybean planted in no-till, high residue fields or fields with high cover crop biomass for slug damage this week. We have seen a sizeable increase in gray garden slug activity this week in New Castle County in fields that had low counts. Thresholds for soybean have never been worked out, and soybean can tolerate considerable stand damage without compromising on yield, or at least enough to offset the cost of a rescue treatment. Rescue treatments for soybean probably should be made before the crop emerges out of the ground. Often times, most if not all of the seed has emerged by the time such an application is made, by this time, slug damage has been done.

Cultural strategies include closing seed slots, row cleaners, and turbo tillage. Pop up fertilizer may help in corn. Ammonia and possibly liquid potash might be used to burn slugs if applied on a warm, humid, still night so that the material comes into direct contact with the slugs. Otherwise, they are unlikely to have significant or lasting effect.

Small Grain
Several calls have come in over the last couple of weeks regarding barley yellow dwarf. There has been more BYDV this year than there has been since the early to mid-2010s. Fields with even low aphid populations in the fall exhibit symptoms. It is possible that some of our stunted plants were infected with the February aphid population increase. Some wheat varieties have some degree of BYDV tolerance, check with your seed salesmen or company agronomist. Seed treatments are an option and should provide between 4 and 9 weeks of aphid control. I reckon a seed treatment would probably cost between 10-15 dollars. Endigo is labeled for barley and should give the longest residual control and may cost a bit less. Sivanto is labeled for both barley and wheat but is a very expensive product. Pyrethroids and OPs are labeled and do a good job killing aphids but have very limited residual activity.

There is an excellent publication detailing what is known about BYDV and observations from multiple states, including proposed thresholds for managing for BYDV, the impact of planting date, and ideal treatment windows. You can find it here:

Continue scouting for armyworm activity, especially in Kent and New Castle counties. Larvae may be present on plants early in the morning, but they tend to hide underneath residue during the day. Armyworm are susceptible to pyrethroids.

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