Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

 

Soybean

Stink bugs continue to be very active, and more reports of fields at or near threshold at R3 were received this week. 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.

The 2022 corn earworm flight is beginning. Open canopy, drought stressed fields are the most attractive to earworm. Flowering soybeans R1-R3 are also highly attractive as moths will feed on nectar. It takes 2-3 days for earworm eggs to hatch, and there tends to be high mortality in early instars. It takes about 6 days for larvae to molt to the third instar. Begin scouting for earworm by the end of next week. If earworms are found, NCSU has a handy threshold calculator worth checking out to determine if a field is above threshold: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html. Remember: corn earworm control with pyrethroids can be inconsistent (see also the efficacy note in the vegetable sweet corn scouting segment). If using a pyrethroid because of the lower price, it is possible that a field may still be above threshold after treatment.

Sorghum

Begin scouting flowering or head-push sorghum for corn earworm. Take a bucket and beat 5-10 sorghum heads in 5-10 locations in the field, counting number of earworms that fall out. Texas A&M has a threshold calculator similar to the North Carolina soybean calculator: https://extensionentomology.tamu.edu/sorghum-headworm-calculator/. While scouting for earoworm, look for signs of sugarcane aphid infestation. So far, reports from North Carolina and Virginia have not indicated elevated activity, but this aphid can reproduce extremely quickly.