Agronomic Crop Insect Scouting

David Owens, Extension Entomologist;

Continue scouting flowering to milk stage sorghum for corn earworm. Earworms generally have a ‘bumpy’ appearance, and in sorghum, a darker striping pattern. The head is orange. Fall armyworm may also be present in heads, and is generally considered to be equally damaging. Fall armyworm are usually gray, although lighter greenish color morphs can be found. Lighter color morphs usually have a dark spot on the side behind the thoracic true legs. The head has an inverted Y faint line and the last abdominal segment has 4 ‘dots’ arranged in a square pattern. One worm per head is generally associated with a 5% yield loss. You can use this to determine an appropriate threshold. Thresholds are generally between 1 and 2 worms, but this can differ depending on control tactic, price of sorghum, and expected yield. Vial testing on this week’s moths indicate near 50% survivorship. Pyrethroids may not provide adequate control by themselves. Use high rates and high pressure if going out with a sorghum head spray.

Corn earworm is active in fields. Be sure to scout double crop fields, open canopied fields, and dry pivot corners the next 3 weeks. Vial testing results on moths indicate near 50% survivorship, indicating a risk that a pyrethroid alone may not provide satisfactory control. If a pyrethroid is applied, be sure to follow up scout a couple of days later to determine efficacy. Stink bugs are also active and are pests up until beans reach later R6 stages. Thresholds are 5 per 15 sweeps, however, if a field is 3 or more, follow up scouting is going to be important, particularly in taller soybean fields. Stink bugs move throughout the canopy and can move deep enough that they may not be captured in a sweep net. Finally, soybean loopers are now active in Virginia. I expect to start seeing moths in our area soon. Generally, the final week of August to the second week of September is when soybean looper populations peak.

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