Monday, September 1, 2014

Whitefly Feeding Causing Soybean Field Edges to be Yellow

In mid-August, I observed yellow patches within a field in Southern Illinois.  A closer look and an insect sweep revealed tiny, whiteflies on the lower sides of leaves.  No other insects such as soybean aphids or two-spotted spidermites were found within infested areas.

Yellow area within a field - whitefly infestation, picture provided by John Howell, Burrus Acount Manager
Yellowing of soybean leaves due to whitefly feeding - picture provided by John Howell, Burrus Account Manager.
 Whiteflies are related to aphids and are in the insect order Homopera.  They are usually found in dry areas and favor warm temperatures (57 - 97 F).  I can only speculate that the whitefly populations started to multiply in areas that had not received much rain until later in August.  Most of the infestations as of now appear to be minor and are often seen on field edges.  Whiteflies have a wide host range and will feed on around 500 species of plants.  A common host is velvetleaf or buttonweed.  I suspect that mowing roadside ditches will promote feeding within soybean field edges.
Whitefly injury to soybean on field edge
Whiteflies can reproduce quickly and will hatch from eggs, pass through 4 nymphal stages, then molt into adults every 18 to 22 days.  The adults and nymphs have mouth parts that will pierce then remove fluids directly from the lower side of the leaf.  Whiteflies can also inject saliva and phytotoxic enzymes into plants.  After whitefly populations feed on lower leaves, symptoms such as yellow leaf speckling, chlorotic areas on leaves, or drying of leaves can appear.  Soybean plants can also become stunted.  Just like aphids, whiteflies can produce honeydew, which can consist of sooty mold on leaves.
Whitefly feeding on the underside of a soybean leaf.
There really is not much known about the effects of whiteflies on soybeans in the Midwest.  There have been numerous reports of whitefly infestations in year's past, but little to no economical damage has been reported.  This year we were lucky not to have other insect problems in soybeans.  As the presence of two-spotted spidermites and soybean aphids, along with whiteflies, can cause complications when it comes to chemical recommendations.  For now, we generally do not recommend insecticides for the treatment of whitefly.  There have been reports of the development of chemical resistance by the whitefly in other agricultural regions.

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