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Hessian Fly Damage

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ST. LOUIS (DTN) — Wheat growers shouldn’t be too quick to diagnose those brown patches in their wakening wheat fields as winterkill.

The Hessian fly threatens to be a significant wheat pest in the Great Plains this year, after several years of little activity. (Photo courtesy USDA-ARS)

The Hessian fly is another possible culprit, as infestations have been reported in many winter wheat fields in Kansas since February, Kansas State entomologist Jeff Whitworth told DTN.

“I’ve seen and heard of more Hessian fly-damaged wheat this spring than I have for the past 10 years,” Whitworth said.

Some varieties might be able to compensate with more tillering this spring, he added. However, already some fields with up to 60% wheat damage from Hessian flies have proven unsalvageable and will be plowed under for soybeans, Whitworth said. The infestations have mostly surfaced in southeast, south-central, and north-central Kansas, but all growers should investigate irregular-shaped patches of dead wheat for the pest, he added.

Oklahoma growers have seen more limited damage so far, said Oklahoma State University entomologist Tom Royer. “I have seen a few infestations, but so far they occurred in fields not planted with a Hessian fly-resistant variety, such as Duster or Gallagher,” he told DTN in an email. “All fields are theoretically at risk, especially if they are growing continuous wheat in reduced tillage,” he added.

The Hessian fly first arrived in the U.S. on infested straw bedding used by Hessian soldiers during the Revolutionary War. It quickly became a regular and major pest of wheat, before resistant varieties were developed in the 20th century to help control it.

Unfortunately, the mild fall last year likely helped the pest overcome wheat farmers’ typical protections against it, Whitworth said.

Usually, planting in mid- to late-October lets growers dodge Hessian fly activity, which ceases in cold temperatures. However, the long, warm fall probably allowed adult flies to continue laying eggs later than usual into the season, up until a severe and sudden mid-November cold snap, Whitworth said.

Moreover, research has shown that warm weather can break down Hessian fly resistance in wheat plants, which is probably why some of the infestations this spring have occurred in varieties with moderate to good resistance levels, he added.

When scouting for the Hessian fly, growers should gently pull back the leaf sheath of the sampled plants and look for tiny, mahogany-colored structures that resemble flaxseeds, where the pest overwinters as pupae. If you spot these structures, the damage from the Hessian fly is already done, Whitworth said. Adult flies lay their eggs in winter wheat in the fall, and the emerging maggots make a meal out of the stem of the plant — damaging or killing tillers — before hunkering down in their flaxseed bunkers for the winter. They emerge from the flaxseeds in the spring as adults, ready to mate and start a new generation of pests.

No rescue treatments exist for the Hessian fly, so winter wheat growers will have to assess the extent of the infestation carefully, Whitworth said.

A field with less than 10% Hessian fly-infested wheat might be able to compensate with spring tillering and recover enough to take the field to harvest. But in fields with infestations over 10%, growers will need to examine their variety and its spring tillering abilities before making the decision whether to plow the field under, Whitworth said.

Even additional spring tillering may not be enough to save an infested field, because the Hessian fly can produce multiple generations in a growing season and continually attack growing wheat plants, Whitworth said. Any spring wheat planted this year will also be at risk, as fly populations will only build up in winter wheat this spring.

Growers who don’t scout now might be surprised to find badly lodged winter wheat from the pest after the plants are mature, he added.

“Hessian fly feeding in the stem can cause plants to lodge just before harvest, and suddenly it looks like pick-up sticks in your field overnight,” he said.

Growers who have problems will have to focus on prevention for next year, he added.

A top priority will be destroying any volunteer wheat this summer and early fall, where Hessian flies can lay eggs and survive until wheat is planted again in the late fall, Whitworth said. Even a small patch of volunteer wheat can house thousands of eggs.

Growers should also select resistant varieties and try to plant wheat as late as possible, he added.

For more information on Hessian fly infestations in Kansas, see Whitworth’s alert here:…

For more details on managing and avoiding Hessian fly infestations, see this KSU article:…and this Texas A&M guide:…

Emily Unglesbee can be reached

Follow Emily Unglesbee onTwitter@Emily_Unglesbee

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