Two-Spotted Spider Mite
Mites are not insects, but can be scouted as you would other insects. Mite damage can occur almost any time during the season, but is usually more prevalent during very dry conditions. It first appears as a slight yellowing of the leaves, which later changes to reddish to purplish or bronze color, particularly in the interveinal areas of the leaf. Mite damage can also be recognized by the presence of fine webbing on the underside of the affected leaves. This webbing often traps blown sand grains.
In severe infestations, spider mites can cause widespread defoliation. Spot check for mites while scouting for other pests. Even with obvious yellowing and defoliation, the presence of an active mite population throughout a significant portion of the field should be confirmed before treating. Populations will begin as individual locations in a field and will radiate out from a “hot spot.” A hand lens is very helpful in spotting the small moving adult and nymph stage mites and their very round shiny eggs on the undersides of speckled or bronzed leaves. A fungus that preys upon mites is often present, particularly under rainy or humid conditions, and may greatly reduce mite numbers while the damage symptoms are still present. If significant rainfall is predicted, do not treat but reassess the mite population a few days after the rain. A significant drop in egg levels often indicates a declining mite population.
Two-Spotted Spider Mite Thresholds
General leaf discoloration (chlorosis, bronzing, or both), plus live mites over most of the field and defoliation from mites in 25 percent or more of the field. (If rain is imminent, delay treatment and reevaluate 3 to 4 days after the rain. If a miticide is used, 2 applications are sometimes necessary.