Agronomic Crop Insect Scouting

David Owens, Extension Entomologist;

Early Season Moth Activity

Trap Location True Armyworm per night Black Cutworm per night
Willards, MD 0 1.7
Salisbury, MD 0.1 2.0
Laurel, DE 0.1 6.0
Seaford, DE 0.7 1.3
Bridgeville, DE 0
Harrington, DE 0.1 1.7
Smyrna, DE 0.3 13.3
Kenton, DE 0.1 2.6
Pearson’s Corner, DE 0 1.6
Sudlersville, MD 0 0.3


Black cutworm larvae have been observed in some fields cutting plants. Most infestations are well below economic thresholds. Cutworms are large enough to cut plants once 300 DD have passed from a ‘significant moth flight’. This is defined as a trap catch of 9 moths or more for 2 consecutive nights. Since we only check our traps once a week, it is more difficult to determine when this happens, but a trap would have to catch at least 18 moths in a week. We had a large number of moths in Seaford and Laurel the week of April 10, spreading to Smyrna the following week. We have now accumulated enough degree days to see large worms. Scout your fields, and especially fields that had living cover crop or living weeds in the middle to end of April. Remember, moth counts in a trap do not mean that your field will have a damaging level of black cutworms. Also, black cutworm, while notorious, is not the only cutworm species present. Whether or not cutworms develop into large worms will depend, in part, on the Bt trait package present in your corn. Trait packages with Cry1F or Vip3A proteins should control cutworm. You can find all of the trait packages effective on cutworm and true armyworm here:

True armyworm developing in cover crop has been observed feeding on corn in nearby states, including Maryland’s eastern shore. Threshold are pretty high, 25% infested plants. True armyworm is only going to be controlled by Vip3A containing traits.

Be sure to watch emerging soybean stands like a hawk. There are three pests that we have to think about when planting soybean: seedcorn maggot, slugs, and bean leaf beetle. The first two do not have good rescue treatment options. We are at generation 1’s peak seedcorn maggot flight activity now. They are favored by cool, wet conditions with very recent cover crop incorporation (within the last few days). You can either delay planting about a week to avoid maggots or plant with an insecticidal seed treatment. With slugs, recent cool weather and rains will favor their activity. Early in the morning or at night, kick some field residue around and you may find them, or you can place a square foot shingle or board or cardboard out in location and count slugs underneath it the next morning. Generally, a good level of concern is 3 or more slugs. This doesn’t mean you will have problems, because slug activity is heavily influenced by environmental conditions. Hot, dry conditions are not favorable for slug activity. Slug bait is an option, but by the time stand loss is observed, damage has already been done. Vertical tillage or turbo-tilling can help disrupt the slugs. By the time a field is replanted, weather conditions may change and then it becomes a question of did the intervention work or the weather is just better? Planting without a neonicotinoid seed treatment can help preserve beneficial, slug-feeding ground beetles. Closing furrows and removing residue around the furrow with row cleaners can also help protect the seed and encourage faster germination. Once seedlings emerge from the soil, they become harder for slugs to kill. Bean leaf beetle are also active. Most feeding is cosmetic; the soybean plant will recover. Thresholds prior to 2nd trifoliate are 2 per foot AND 25% stand reduction. After this stage, thresholds increase dramatically to 2-3 per plant and 30% defoliation.

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