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Hessian fly infests Arkansas wheat

Hessian fly infestations have been found in some areas of Arkansas this spring. The damage was evident in lodging that occurred following spring storms. Many growers blamed the lodging on the storms, but closer examination showed that many of the lodged plants were infested with the Hessian fly.

Larvae of the Hessian fly feed on the stem, underneath the leaf sheath near the node. This feeding will often weaken the stem, resulting in lodged plants.

We saw from 10 to 50 percent lodging in some areas. The Hessian fly is responsible for a good part of this lodging.

Delayed planting date is a common cultural practice used to reduce the likelihood of infestation in a wheat crop, but planting date does not seem to have had any effect on the fields that were infested this year. In fact, many of the fields that were planted in late October seemed to have higher levels of the fly than earlier-planted fields.

This may be due to the extremely dry October we experienced last year. In northeast Arkansas, there was no significant rainfall until early November. The Hessian fly adults emerge from puparia after a good soaking rain. This may account for the infestations showing up in those fields planted in October. Due to the weather conditions at that time, the fly apparently did not emerge in good numbers until early November and then began infesting the wheat crop.

While there is nothing growers can do to protect this year's wheat crop from the fly, there are some things that can be done after harvest that will reduce populations this fall. The fly survives the summer months in the wheat straw in what is commonly referred to as the “flax seed” stage. This stage is actually a late instar larva enclosed in a hard, dark-brown covering about the size and color of a flaxseed.

While in this developmental stage, the fly can survive adverse environmental conditions such as extreme hot and dry weather as well as extreme cold.

These larvae can be found in the straw, underneath the leaf sheath near a node. Larva will remain in this stage throughout the summer months until September or October, emerging after a good soaking rain.

Growers should destroy wheat straw after harvest either by burning or disking. Disking once does a good job of burying the larva deep enough to cause significant mortality. However, research has shown that further disking actually decreases fly mortality. It is believed that subsequent disking may bring the small flax seed stage larva back to the surface where they have a better chance of survival.

The increase in the fly may be the result of increased no-till or reduced-tillage in the state. Some growers leave the wheat stubble in the field, leaving the field fallow or double-cropping with no-till soybeans. This practice significantly increases the survival of the fly for next growing season.

Coupling this with a dry fall results in basically no fly-free planting date in Arkansas and high populations of the fly infesting some wheat.

Growers should examine stubble left in fields to determine if any fly reside is present. They should look for the small flax seed stage near a node. Information on proper identification can be obtained from University of Arkansas Cooperative Extension Service offices.

If no flies are found, no-till practices can be initiated without contributing to the fly population this fall. However, if significant numbers of flaxseed stage flies are found, stubble should be destroyed as outlined above.

Glenn Studebaker is an Extension entomologist with the Cooperative Extension Service, University of Arkansas. e-mail: [email protected]

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