Some soybean fields in northern Illinois are currently infested with whiteflies (Bemisia tabaci) said Mike Gray, University of Illinois professor of entomology and crop sciences Extension coordinator.

B. tabaci is a complex of 11 well-defined high-level groups containing at least 24 morphologically indistinguishable species. The common names of this complex include sweetpotato or silverleaf whitefly.

"If hot and dry conditions persist, I anticipate infestations of whiteflies will intensify along with twospotted spider mite challenges in the same fields," Gray said.

In 1988, whiteflies were reported in soybean fields in northern Florida. Since then, infestations have been more common in the soybean fields of the Southeast, with few infestations reported in fields in the north-central states. However, in hot and dry summers, whitefly reports begin to surface in the Corn Belt. The host range for whiteflies is impressive, with over 500 species reported for the sweetpotato whitefly.

Whiteflies pass through four nymphal stages after hatching and then molt into adults. Adults and nymphs have piercing and sucking mouthparts. They remove fluids directly from plant tissue, mostly from the lower surface of leaves. Leaves may become discolored and begin to wilt. Stunting of plants also may occur under heavy infestations.

In addition to removing plant fluids, whiteflies inject saliva and phytotoxic enzymes into plants. Like aphids, they produce honeydew, which can collect on the surface of leaves, stems, and pods and subsequently develop a sooty mold. Leaves covered with sooty mold have reduced photosynthetic efficiency, which contributes significantly to yield losses.

Development of whiteflies occurs when temperatures are between 57 to 97ºF. The average generation time lasts 22 days (range 18 to 30 days). Management decisions for whiteflies will be complicated by the fact that most fields are likely to have spidermites along with some Japanese beetles.

The prolonged hot and dry weather also will intensify infestations and make soybean plants more susceptible to yield loss.

"Under the very hot temperatures forecast for the next week, pyrethroid effectiveness and residual activity will not be enhanced," said Gray. "Let's hope the state begins to receive some rain soon."