Winter grain mite and possible return of the Hessian fly may be of concern for Oklahoma wheat producers.

Jeff Edwards, OSU Extension small grains specialist and the Warth Distinguished Professor of Agronomy, discussed both pests in recent blogs at www.osuwheat.com.

“Over the past week, I have received a few reports of winter grain mite activity in southwest Oklahoma,” Edwards writes. “Winter grain mites are small (about 1 mm long) with black bodies and orange-red legs. Winter grain mites complete two generations per year and the adults can live for up to 40 days. The generation we are dealing with now resulted from over-summering eggs laid last spring. The second generation peaks in March/April and results from eggs laid in January/February.”

Edwards recommends that wheat growers scout fields to identify infestations. Scouting early in the morning or late in the evening may be best since the mites “are light sensitive and prefer calm air to windy conditions.” Cloudy days are also good for scouting.

“Be sure to look under residue in no-till fields and under clumps of soil in conventional-till fields,” he says.

 

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These mites feed by piercing plant cells in the leaf, which results in stippling. “As injury continues, the leaves take on a characteristic grayish or silverish cast.  Winter grain mites are more likely to cause injury in wheat already stressed from lack of moisture or nutrients (deficiency). Also, freeze injury can easily be confused for winter grain mite injury.”

Edwards says no economic thresholds have been established for winter grain mite control. “Healthy, well-fertilized wheat plants generally outgrow injury, so it takes large numbers to justify control,” he says. “If injury and large numbers of mites (around 10 per plant) are present in wheat (planted) for grain only this time of year, you might consider control. If the wheat is to be grazed, I would simply monitor the situation in most cases and only spray if injury becomes severe.”

Spray options are limited. Few insecticides include winter grain mites on the label and most also have grazing restrictions. “Malathion and methyl parathion have been shown to provide effective control in the past,” Edwards says.  He suggests growers check the OSU Current Report 7194 Management of insect and mite pests in small grains for a more complete listing of available pesticides.