Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Early Season Moth Trapping
The black cutworm flight continues in the Laurel and Harrington areas. Be sure to check crops going into late cover crop termination fields. Recent southerly winds and warmer weather have most likely contributed to this increase. Also, for the second year in a row, our trap in the Smyrna area is catching very high numbers of true armyworm. It will take a couple of weeks for moths to lay eggs, those eggs hatch, and larvae begin feeding on wheat. Please note that trapping data is meant to be correlative over time, we do NOT have thresholds or make recommendations for individual fields or crop considerations based on them. We do not know at what point these traps indicate a potential problem, short of comparing true armyworm counts to some long term data collected by University of Kentucky. Many thanks to Joanne Whalen for assisting with trapping efforts.

Location # of Nights Total Catch
Willards, MD 6 2 21
Laurel, DE 7 53 86
Seaford, DE 7 21 43
Sudlersville, MD 7 (4/8) 3 2
Harrington, DE 7 136 74
Smyrna, DE 7 576 9
Middletown, DE 7 63 18

Small Grains
In addition to the armyworm note for Smyrna, we have reached the cereal leaf beetle target degree days for peak egg lay. In previous years, we have attempted to use this threshold but cereal leaf beetle counts have been too low. In 2018, we started seeing our first eggs around this target. When Bill Cissel and I surveyed for cereal leaf beetle, the greatest concentration was at the Wye REC in MD. Threshold for cereal leaf beetle is 25 eggs or larvae per 100 tillers. Aphids are generally low this year.

Corn and Soybean
The first of our corn and soybean crop is going in the ground. Next week’s weather looks favorable to slugs; cool weather, recent rains, and some more in the forecast to keep them happy. We picked up our first gray garden neonates four weeks ago, but now we are seeing more of them, suggesting that we are nearing peak egg hatching.

Save riskier fields for later in the planting season if possible. Fields that have been turbotilled in the fall or this year are much less likely to have significant slug populations. Remember to avoid adding insecticide in burndown herbicide applications to conserve slug predators. Having said that last point, if planting into a green cover crop that has not died prior to planting, scout it carefully. We have been picking up a greater black cutworm flight in our pheromone traps than last year or the year before. These moths may have been aided by strong southerly winds last week. I do not make specific recommendations on cutworms based on pheromone traps, but monitoring them is useful for starting a degree day calculator to estimate when larvae may be big enough to cut corn.

Finally, a discussion of tillage would be incomplete without mentioning another early season pest that is favored by tillage: seedcorn maggot. Seedcorn maggot like incorporated organic matter. Right now in Georgetown we are in between generations. We tilled under Austrian winter peas and chicken manure in a field setup for seedcorn maggot three weeks ago. Most of the larvae in the field are almost done with their feeding and are beginning to pupate, suggesting that the next 7 to 10 days pose lower risk for seedcorn maggot. Seedcorn maggot is another pest favored by cool soil temperatures. As with slugs, anything that favors earlier vigor and faster growth will go a long way towards reducing stand loss risk to seedcorn maggot.

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