Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Soybean

Continue scouting for defoliation, stink bugs, and podworms. Generally, stink bug threshold is 5 bugs per 15 sweeps (nymphs and adults, brown, green, brown marmorated and dusky all combined). I suspect that a lower threshold may be justifiable in Plenish soybean, perhaps ~ 4 bugs per 15 sweeps.

For worms, check out NCSU’s handy threshold calculator. Keep in mind that good efficacy among pyrethroids is not guaranteed. I have smoked earworms with pyrethroids in soybean before, and I have also had poor efficacy in spray trials. I generally think of Hero and Baythroid providing greater efficacy than others. Please note though that I have not tested lower rates of Hero (rate range is 4-10.3 fl oz). If you are at or above a threshold for a more expensive “worm” product (examples in no particular order include Intrepid Edge, Steward, Vantacor, Besiege, Radiant, Blackhawk).

Sorghum

Scout heads for earworm. Beat 50 heads into a container and count earworms, fall armyworm, and sorghum webworm. Webworms are not very common, small, and have a higher threshold than the earworm and armyworm. Texas A&M has a headworm calculator: https://extensionentomology.tamu.edu/sorghum-headworm-calculator/. In previous years, earworms have been spotty, apparently depending heavily on when the sorghum is pollinating in relation to when moths are flying; much in a similar way to sweet corn. Unlike in sweet corn, there is a high level of mortality in first and second instars.

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