Scout for Spider Mites in Dry Beans

The first reports of spider mites being found on field edges of soybeans came in this week from West Fargo, ND and Crookston, MN, according to the NDSU Extension Crop & Pest Report. Spider mites are small (1/50 of an inch long) and magnification is usually required to see them. A 10x hand lens is helpful in seeing spider mites
in the field.
Spider mite infestations typically are first noted near field edges, so start scouting at field edges to see if spider mites are present. A quick sampling procedure to determine whether mites are present is to hold a piece of white paper below leaves, then beat the leaves to dislodge the mites.
Spider mites appear as tiny dust specks and they move slowly after being knocked off the leaf. Another method is to pull plants and examine the undersides of the leaves for
mites and webbing.
The threshold for dry beans is when heavy stippling on lower leaves occurs with some stippling
progressing into middle canopy. Mites may be present in middle canopy with scattered colonies
in upper canopy. Leaf yellowing on lower leaves common.
If fields are above the action threshold for spider mites, then an insecticide or a miticide treatment may be necessary. Most of the insecticides and miticides available for control of spider mites in dry beans are listed here on page eight.