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.

Hessian fly

Hessian fly may also cause trouble this year.

Edwards says development of Duster wheat variety reduced the effect of Hessian fly infestations “after building to alarming levels in 2006.  Back then, it appeared that Hessian fly was going to be the demise of no-till wheat in Oklahoma. Early planting, lack of crop rotation, and no-till, monocrop wheat all create a favorable environment for Hessian fly, and several early-sown fields were completely lost to the Hessian fly in 2006 and 2007.”

About that same time, OSU released Duster, an excellent wheat for grazing but with good grain yield potential. Duster also happened to be Hessian fly resistant. “This resistance was a clear proton torpedo in the thermal exhaust port of the fully operational Hessian fly Death Star (to use a Star Wars metaphor).”

The fly has been quiet for several years. “Over the past four years, I received very few calls about Hessian fly,” Edwards says. “It seemed that the adoption of Duster and unfavorable environmental conditions resulted in a dramatic reduction in Hessian fly in Oklahoma.”

But it may be back.  “There are indications that Hessian fly is making a return,” Edwards says. “I have received calls about Hessian fly this fall, most from southwest Oklahoma. In most cases, producers had either switched to a newer variety that was not Hessian fly resistant or changed to a non-resistant variety because they were displeased with Duster’s performance the past two years.”

Prevention

Prevention is the key to managing the pest. “There are no curative treatments for Hessian fly in wheat. If you currently have a field infested with Hessian fly, the first step is to assess the level of infestation. If a plant with four viable tillers has one tiller infected, the impact on yield might not be great, as we could have additional tillering in late winter. A field with most tillers infected is likely a good candidate to graze out.”

He says preparing for next year should begin now. “It is never too soon to be thinking of how to limit the impact of Hessian fly on next year’s crop. Planting a resistant variety still remains the most effective technique in Oklahoma for dual-purpose wheat farmers. To determine which varieties are resistant, consult a current OSU Wheat Variety Comparison Chart.

“Insecticide seed treatments are effective early in the season,” he adds,” but typically do not last long enough to provide season-long control in Oklahoma.” Other options include cultural practices such as crop rotation and delayed planting until mid-October. Those measures might not work for all operations.

Growers should take the pest seriously. Without adequate precautions, wheat used for grazing may suffer significant damage and can be pulled out of the soil by grazing cattle, leaving thinner stands for harvest.

Pulling some wheat stalks is an important diagnostic practice. “Above-ground appearances can be deceiving, so it is important to pull plants to ensure crown roots are there, even if the plants appear large enough for grazing.

“It is also important to prepare fields to measure first hollow stem prior to turning cattle on wheat pasture. Grazing delays plant development; therefore, first hollow stem has to be checked in a non-grazed area.”

The check plot need not be large and can be created with a panel exclosure or by moving an electric fence in a few feet. “The key is to plan for the non-grazed area now so you can measure first hollow stem in February.”

They key for both pests, Edwards says, is to assess infestation levels. Knowing what’s there provides producers information they need to develop management strategies.

 

Also of Interest:

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