Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Stored Grains
Recently a question came in regarding what products are labeled for stored grains. Many easily found extension fact sheets are also nearly 7 years old or older. South Dakota State University’s Dr. Adam Varenhorst wrote an excellent fact sheet recently that may be helpful, including a list of current products: Please also note that the use of chlorpyrifos is no longer an option where it might come into contact with agricultural produce including grain bins.

Pay attention to flowering alfalfa for blister beetles. Recently we have seen large numbers of yellow striped blister beetles in non-crop areas. There are no thresholds for blister beetles. Insecticides can reduce live blister beetles, but if the dead insect does not fall completely out of the canopy, it could still cause problems in the cut forage. Nebraska’s Gary Stone writes that “haying equipment without conditioners has shown to reduce the number of dead beetles. If the hay is harvested in this manner and the hay is allowed to dry in the windrows, the majority of Blister beetles can move out of the windrows before the hay is baled. The use of sicklebar mowers has shown an increase in Blister beetles in the harvested crop because the Blister beetles are crushed driving over the cut hay and then picked up when raked into windrows and baled.”.

Scout for potato leafhoppers. By the time yellowing leaf margins are observed due to hopperburn, yield has already been impacted. Thus, routine scouting needs to be performed, especially in alfalfa that is not ready to harvest. Cutting alfalfa will kill nymphs and drive adults out of the field for a period of time. Leafhopper threhsolds per 100 sweeps increase as plant size increases, but can vary anywhere from the low teens to more than 100 per 100 sweeps. For more information, visit our insecticide recommendation guide (with information borrowed from Penn State

Grasshoppers and worms are the most abundant defoliators present in soybean fields. Grasshoppers seem to be especially thick along grassy, sprayed ditchbanks and vetch cover crops. Be sure to scout areas with late terminated cover crops and double crop soybeans as they emerge. Defoliation thresholds for vegetative soybean are very high, around 40%, but once we progress into R2-R3, defoliation thresholds decrease substantially. If a treatment for grasshoppers is deemed to be necessary or desirable, high pyrethroid rates should be used, low to mid rates sometimes do not result in significant grasshopper reduction. Other products for which we have seen very good efficacy in limited trials include dimethoate at a 1 pint rate and Elevest tank mixed with MSO (per Elevest’s label). Given Elevest’s good efficacy in a 2020 trial, I expect Besiege would also have similar efficacy. Curiously, Vantacor (formerly Prevathon) and Elevest both advise to add MSO, but this stipulation is not present on the Besiege label.

Begin looking for and noting fields with Dectes stem borer.

Some of our earliest fields are starting to move into the R3 stage. Pay attention to stink bug numbers in these fields. R3-R5 are the most susceptible soybean stages to stink bug damage. Current thresholds are 5 per 15 sweeps.

Field Corn
Continue scouting tasseling field corn for stink bugs. They will most likely be present along field edges, especially edges that border grassy areas or previous small grains. If a significant number of stink bugs are found along edges, check field interiors. Check field interiors for late planted fields into late terminated small grain cover crop. If stink bugs are present only along edges, a simple border spray may provide good control.