Twospotted Spider Mites, Whiteflies, and Potato Leafhoppers: Common Inhabitants of Many Soybean Fields

August 13, 1999
We've discussed management strategies for twospotted spider mites and potato leafhoppers in soybean fields in many previous issues of the Bulletin. In some drought-stressed areas of the state, isolated pockets of twospotted spider mites persist, and some localized rescue treatments (such as in Greene County) are being applied. Potato leafhopper populations also remain impressive throughout most of Illinois. Twospotted spider mites will most likely continue to remain a problem in drier areas of the state. Potato leafhoppers will persist until several hard frosts have taken place; there is not much relief in sight.

Although whiteflies are typically more of a curiosity in soybean fields throughout much of the Midwest, reports of infestations in soybeans have increased in many southeastern states. In northern Florida in 1988, the sweetpotato whitefly began to infest soybean fields. Significant reductions in soybean yields have occurred due to whitefly infestations. Damage to soybeans appears to be more acute in warm and dry summers. Whitefly infestations in soybeans throughout the Corn Belt have not been considered to be of major importance; however, these insect pests may become increasingly worthy of our attention. Sweetpotato whiteflies have a large host range and have been collected from 506 species (74 families) of plants.

Whitefly nymphs and adults have piercing and sucking mouthparts. They can be found most readily on the undersurface of leaves removing sap from plants. Large densities of whiteflies in soybeans may result in the development of chlorotic spots on leaves, wilting, and stunting of plants. These symptoms are caused by the introduction of saliva and/or enzymes into soybean plants. Similar to corn leaf aphids, whiteflies produce honeydew. This sugary solution can coat leaves, stems, and pods. A sooty mold can subsequently begin to develop on the honeydew.

No clearly defined thresholds are available for whiteflies in soybeans. The combination of mites, potato leafhoppers, whiteflies, and pod feeders will complicate treatment decisions in soybeans for the next several weeks. Please let us know if whitefly infestations are a severe problem in your area of the state.--Mike Gray

Author: Mike Gray