Issue No. 13, Article 3/June 29, 2012
Whitefly Infestations Reported in Some Northern Illinois Soybean Fields
Some soybean fields in northern Illinois are currently infested with whiteflies, a pest with a complicated taxonomy. A 2011 Annual Review of Entomology article indicated that "B. tabaci is a complex of 11 well-defined high-level groups containing at least 24 morphologically indistinguishable species" (DeBarro et al., "Bemisia tabaci: A Statement of Species Status," Vol. 56, pp. 1–19). The common names used most often include sweetpotato or silverleaf whitefly.
I anticipate that if hot and dry conditions persist, whitefly infestations will intensify, along with twospotted spider mite challenges in the same fields. Historically, whiteflies have caused more problems in soybean fields in southeastern areas of the United States. In 1988, whiteflies were reported in soybean fields in northern Florida. Since then, infestations have been more common in southeastern soybean fields. In most seasons, whiteflies are far less common in north-central states, but in hot and dry summers, 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 following hatch from eggs and then molt into adults. Adults and nymphs have piercing and sucking mouthparts and remove fluids directly from plant tissue, which occurs primarily from the lower surface of leaves. Leaves may become discolored and begin to wilt. Stunting of plants also may occur where infestations are heavy. In addition to removing plant fluids, whiteflies inject saliva and phytotoxic enzymes into plants. Similar to aphids, whiteflies 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, contributing to significant yield losses.
Development of whiteflies occurs between 57 and 97°F with an average generation time of 22 days (range 18 to 30 days). Management decisions for whiteflies will be complicated by the fact that most fields are likely to have spider mites 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. Let’s hope the state begins to receive some rain soon.--Mike Gray