Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

Field Corn
Western corn rootworm is active in corn fields that have not been rotated in north and western Kent County and New Castle County. If you observe more than one beetle per plant, there is potential for significant rootworm populations in next year’s corn. Beetles are highly attracted to the silks and pollen. If you see them in your field and you are planning to put corn in the same field next year, consult the Handy Bt Trait Table for selecting an effective trait package to prevent root pruning:

Fall armyworm is active in whorl stage sorghum, but treatment is only advised if 75% of whorls are infested. A new sorghum pest management sheet was posted to the UD extension pest management page earlier this year:

All of the typical defoliators are present in soybean. In some full season bean fields defoliation had reached 10%; such fields need to be examined closely over the next week or so to make sure that there are not enough defoliators to go over the threshold. Also pay attention to drought stressed fields that are not growing quickly as defoliation will have a greater impact on them than on irrigated beans. Spider mites continue to be active, especially along field edges with ditchbanks by roads. I have a glorious mite outbreak at Carvel where my untreated check plot is pretty obvious with yellowing plants.

Some fields have large numbers of grasshoppers in them and also blister beetles. Be careful when reaching into the sweep net! Low numbers of podworms and stink bugs can be found in full season fields, but are not considered much of a threat until R3 – R4, beginning pod to full pod stage.

Continue scouting for potato leafhopper. While sweeping, pay attention to blister beetles. Blister beetle infested alfalfa that is about to be cut should not be fed to horses. Pay attention to PHI’s of pyrethroids, and beware that dead beetles might not ‘fall out’ of the canopy and can still cause problems. Beetles are attracted to flowering alfalfa, if you observe a large number of grasshoppers and beetles in weedy edges, you may want to consider making your next cut before flowering.