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The Hessian Fly: A Pest of Wheat in North Carolina

North Carolina Cooperative Extension

Prepared by:
S. Bambara and J.W. Van Duyn, Extension Entomology Specialists

N.C. Agriculture Extension Service, AG-368

Dated 8/86 (revised 2/95) Placed on the Web 3/95 by the Center for Integrated Pest Management


The Problem

The Hessian fly, traditionally a pest of wheat grown in the Midwest, has been an infrequent pest of wheat in North Carolina but could easily be a serious pest of this important crop. Recent changes in wheat production have permitted this insect to reach pest status in North Carolina, and some wheat fields have suffered extensive losses as a result. Currently, infestations appear to be the greatest in the Piedmont. The fly prefers wheat but will also attack barley and rye.

Accidentally introduced into the U.S. in the late 1700s, the Hessian fly became the most damaging pest of wheat in the Midwest and Great Plains. The use of resistant varieties and "fly-free" sowing dates has greatly reduced the impact of this insect. Unfortunately, the resistant varieties used in the Midwest are not well-suited for use in North Carolina, and in some parts of the state "fly-free" dates may not exist.

Description

The adult is a small, long-legged, two-winged insect that resembles a sorghum midge or small mosquito. The reddish female flies are about 4 mm long (1/6 inch), while the slightly smaller males are brown or black.

The eggs, deposited on leaves, are red and the newly hatched larva or maggot is also red for 4 or 5 days before turning white. As the larva matures, a translucent green stripe appears down the middle of its back. When full grown, the maggot is about 4 to 5.5 mm long (1/6 to 1/4 inch). The maggot transforms into an adult fly inside a case called a puparium that is dark brown and resembles a flaxseed in size and shape. These puparia, or "flaxseeds," are located on the leaf surfaces.

Life Cycle

The Hessian fly has four distinct life stages: egg, larva, pupa, and adult or fly. In the Midwest, there are two generations each year (the spring or first generation and the fall or second generation). Hessian flies in North Carolina probably have three or more generations each year, except in the western Piedmont and Mountains, where they may have two. These additional generations are the result of warm weather in the fall.

Hessian flies can attack any wheat crop that is fall-planted and spring-harvested. In late August and September, adults emerge from "flaxseeds," which survived the summer on wheat stubble, and lay eggs on the upper leaf surfaces of fall-seeded wheat. Adult life is short, lasting an average of only two or three days.

Eggs hatch within a few days and the tiny maggots migrate to the base of the leaf sheath where they feed between the sheath and the stalk for 4 to 6 weeks. They then change to the puparia or "flaxseed" stage.

The pupae that survive the winter emerge as adults in the spring to begin the next generation. The maggots of the spring generations feed by extracting juices from the stem at the crown or joint, and after approximately 4 weeks, they enter the "flaxseed" stage to pass the summer on the stubble. In late August through September, flies emerge to deposit eggs on fall-planted and spring-harvested wheat.

Damage to Small Grain

Maggots feeding on wheat in the fall weaken and stunt plants. This may result in greater winter kill of plants and reduced spring tillering. Stems infested by the spring generation may die but usually lodge before harvest from feeding activity on the first or second node or joint. Frequently the heads of infested plants are smaller and poorly filled with low-quality grains.

Conditions Favoring the Hessian Fly

Trends in conservation tillage and no-tillage of soybeans following wheat has led to more remaining stubble and late-season volunteer wheat. The use of small grains (particularly wheat) for cover crop or grazing also helps ensure high survival and reproduction of Hessian flies. Early planting (before mid-October) of small grains and the use of largely nonresistant varieties have been added factors. The estimated net results of these practices are that adult Hessian flies have a susceptible host available at each generation and that flaxseed-stage flies pass the summer without being destroyed. More Hessian flies and yield losses are the final result.

Management

While Hessian fly infestations cannot be predicted yet, current production practices favor continued problems with this insect. As a result, the use of cultural practices is necessary to reduce the threat this insect poses in wheat production

1. Resistant Varieties. Although the Hessian fly is managed in the Midwest using resistant wheat varieties, these do not perform well in the Southeast. The southern varieties -- Coker 9543, Coker 9134, and Coker 9835 -- have shown some resistance against some fly biotypes. Programs are under way to evaluate and select resistant wheat varieties that are adapted to the Southeast and our fly biotype.

2. Destroying Volunteer Wheat. Flies emerging in the late summer or early fall will lay eggs on any available host plant, including volunteer wheat. If this wheat is destroyed, the earliest emerging flies have fewer egg-laying sites, thereby reducing the spring generation that might attack nearby wheat grown for grain.

3. Harvest and Residue Destruction. By harvesting wheat early and disking under or burning stubble, much of the population can be eliminated. Disking the stubble completely under is more effective than burning.

4. Rotation. The Hessian fly is a weak flier, so rotation of crops over a wide area can help reduce infestations. Never plant wheat in the same field two years in a row, especially if no-tillage practices have been followed.

5. Planting on Fly-Free Dates. Since the fly lives only a short time in the fall, delayed planting of wheat can help eliminate the overlap between the presence of flies and newly emerged wheat. Wheat planted in early October will most likely be susceptible to attack. The fly-free date is simply the date to sow wheat that will ensure emergence of the wheat after all the flies have died. Approximate fly-free dates are after October 16 in the northwestern portion of the state and after November 1 in the southwestern portion. The rest of the state may experience more than one fall generation and, as a result, the fly-free date may prove ineffective in some years. One could expect to significantly reduce infestation in most instances by planting after mid-November.

For such a program to be most effective, growers would need to combine all the above management tools throughout the community. Failure to do so in one field will allow the fall generation to develop and then spread to adjacent late-planted fields the next spring. Additionally, the use of wheat as a cover crop or forage frustrates this effort by providing the fly with more plant hosts.

6. Chemical Control. One Hessian fly has infested a field, chemical control practices are not effective. In southeastern counties where fly problems may be perennial, application of disulfoton at planting may be helpful.

Life Cycle of Hessian Fly in North Carolina. Below are photographs which show various stages in the life cycle of the Hessian fly and wheat damaged by the fly. All photgraphs were taken in Benton County, Washington in 1980-81, except the stunted wheat, which was taken in San Juan County, Washington in 1978. All photographs were taken by K.S. Pike, except the thin wheat stand was taken by M. Glazer.