Biology And Management
Of Hessian Fly In Wheat

In 2008 and coming years, entomologists expect the risk of economic losses from Hessian fly to be as high, or higher, than they were in the 1980s. Reasons for this include increased wheat acreage, supply shortages of Hessian fly.resistant wheat varieties, widespread occurrence of a strain of Hessian fly that overcomes resistance in most wheat varieties, increased conservation tillage, and disrupted crop rotation schemes as farmers plant the crop that offers the best promise for an economic return. A last and very important factor is that phorate and di-syston insecticides can no longer be used at planting to control Hessian flies. This publication discusses the biology of the Hessian fly and provides suggestions for managing this insect.

Historically, Hessian fly has caused the greatest problems in the southern two-thirds of Alabama. Outbreaks of this insect have occurred periodically in the United States since the mid 1800s.

The Hessian fly is believed to have been introduced into Long Island, New York, in straw bedding used by Hessian soldiers during the Revolutionary War. Hessian fly prefers to feed on wheat, but may also infest triticale, barley, and rye; Hessian fly does not attack oats or ryegrass.

Description and Life Cycle

The maggots (larvae) hatch from the eggs after 3 to 10 days. Hessian fly maggots cannot live in the open, so they crawl down to their preferred feeding site, at the base of a leaf sheath, between the sheath and the stem. In the fall, the maggots crawl down to the crown of the plant. As the wheat stem elongates, maggots are usually found just above a leaf node. Infestations of Hessian fly tend to be found further up the plant as the stem elongates, because females prefer to lay eggs on newly emerged leaves.

Newly hatched maggots are reddish brown and about ¹/50-inch long. As they grow, they become white, then greenish white, and grow to be about ³/16-inch long (Figure 3). The maggots feed by scraping the stem, then sucking up the sap that oozes out of the wound. The maggots feed for 14 to 30 days.

The last stage of the maggot is spent inside the "flaxseed." The flaxseed is a shiny, brown protective case about ¹/8-inch long (Figure 4). It is built from the insect's skin, and named for its resemblance to a seed from the flax plant.

If weather conditions are favorable (between 40 to 80°F), the Hessian flies will pupate (transform into adults) inside the flaxseed. Adults then emerge and start a new generation. If it is too hot or cold, Hessian flies remain as maggots inside the flaxseed until the weather moderates. It is not uncommon to find Hessian fly maggots or flaxseeds stacked up one behind the other, particularly in heavy infestations (Figure 5).

There are 4 to 6 generations per year of this pest in the South. The entire life cycle requires about 35 days at 70°F, longer at cool temperatures. Generations tend to overlap. The pest oversummers as flaxseeds in wheat stubble. The first generation in September is generally on volunteer wheat or on wild grass hosts, the most important of which is little barley. Then there are often two more generations in the fall and early winter.

Maggots continue feeding as long as temperatures are above 40°F. In spring, adults emerge, become active when temperatures reach between 50 to 60°F, and start a new generation. There is usually one spring generation in northern Alabama, and there may be two spring generations in southern Alabama.

Damage

If fall infested tillers do produce grain heads, these heads are small and the stems are stunted. Spring infested plants have weakened stalks, which can lead to stem breakage and lodging. These plants also have poorly filled, smaller grain heads. Hessian fly reduces forage production of winter wheat, but does not greatly affect wheat forage quality.

Management of Hessian Fly

Planting Resistant Varieties of Wheat

Plant breeders try to stay ahead of the biotypes by producing wheat varieties with different resistance genes. These resistance genes are usually given the letter H and a number, for example, the H6 gene, the H7H8 gene, etc. Unfortunately, the Hessian fly can overcome host plant resistance mechanisms, resulting in the formation of new strains, called biotypes (as strains are discovered, they are named with letters). Hessian fly biotypes look identical to each other, but differ in the varieties they can develop and reproduce on.

For southeastern Alabama, there are many wheat varieties that have resistance to the prevailing biotypes of Hessian fly (Table 1). Most of these contain the H7H8 gene for resistance. For more information on Hessian fly resistant varieties, consult the University of Georgia Hessian fly screening test results from Plains (see the insects section of "Small Grain Updates" for the most recent year). The biotypes of Hessian fly at Plains are similar to those that occur in southeastern Alabama.

Only a few wheat varieties are resistant to biotype L, which occurs in northern and in western Alabama (Table 1). Breeding lines with biotype L resistance should result in more Hessian fly resistant varieties for these areas. The University of Georgia tests from Griffin, Georgia, will provide some guidance on what varieties do well under pressure from biotype L.

Table 1. Wheat Varieties That Are Resistant or Susceptible to Hessian Fly

Resistant to most southern strains of Hessian fly1	AgriPro Hickory, AgriPro Crawford, AgriPro Magnolia, AGS 2000, AGS 20102, AGS 2020, AGS 20262, AGS 2485, AGS 2060, Florida 304, GA-Dozier, GA-Gore, GA-Stuckey, Madison, Novartis Coker 9134, Novartis Coker 9766, Novartis Coker 9835, Oglethorpe2, Pioneer 2555, Pioneer 2566, Pioneer 2580, Pioneer 2628, Pioneer 26R31, Pioneer 26R38, Pioneer 26R612, SS 8641, Saluda, Stacy, USG 3592
Susceptible to most southern strains of Hessian fly	AgriPro Mason, AgriPro Panola, AgriPro Savannah, AGS 2031, AGS 2050, Clark3, Clemson 201, Dominion, Fleming, Florida 301, Florida 302, Florida 303, Hunter, Jackson, Jaypee, McIntosh, Novartis Coker 9227, Novartis Coker 9543, Novartis Coker 96634, Novartis Coker 9803, Novartis Coker 9511, Novartis Coker 9553, Novartis Coker 9700, Novartis Coker all 3-digit lines, Pioneer 2548, Pioneer 2643, Pioneer 2684, Pioneer 2691, Pioneer 28974, Pioneer 26R12, Pioneer 26R15, Pioneer 26R22, Pioneer 26R24, Pioneer 26R87, Roberts, SS 520, SS 524, SS 535, SS 560, SS 83084, SS 8404, Tribute, Verne3, Wakefield, USG 3209, USG 3295, USG 3477, USG 36654, USG 3910, Vigoro V9510, Vigoro V9412
1Resistant to Biotypes E, G, M, and O. 2Varieties with resistance to Biotype L (see text). 3Contains Hessian fly resistance genes that are no longer effective in the South. 4Moderately resistant to Biotypes E, G, M, and O. Variable results observed in field, depending on Hessian fly pressure.

Variety recommendations change from year to year. Check the latest version of "Small Grains Insect, Disease, and Weed Control Recommendations," in Extension's ANR-500-A, Alabama Pest Management Handbook, Volume 1.

Practices that Reduce Number of Hessian Flies

Control of volunteer wheat well before planting is recommended because Hessian flies are attracted to volunteer wheat when they emerge in September. Wildlife plantings of wheat, which are often planted early, can be a source of Hessian flies.

Crop rotation helps reduce the chance of infestation by Hessian flies, but is not infallible, because Hessian fly adults will fly up to a mile in search of host plants.

Practices that Prevent or Avoid Fall Infestation

Table 2. Recommended Planting Dates for Wheat in Alabama

	Wheat Planted For
	Grain	Forage Plus Grain	Forage Only
North	Oct 15 - Nov 1	Sept 15 - Nov 1	Aug 25 - Sept 10
Central	Oct 15 - Nov 15	Sept 15 - Nov 1	Sept 1 - 15
South	Nov 1 - Dec 1	Oct 1 - Nov 15	Sept 15 - 30

Few insecticide options are currently available for control of Hessian fly. At-planting granular insecticides, such as Di-Syston or Thimet are no longer registered for use on wheat and cereal grains. The seed treatment Gaucho 480 or Gaucho 600 provides fair to good control of fall infestations of Hessian flies when applied at the high rate of 0.06 pound (ai) per 100 pounds of seed. Cruiser 5FS applied as a seed treatment at the maximum rate of 1.33 ounces/cwt of seed also provides suppression of fall infestation. The low rates of Gaucho and Cruiser (1 fluid ounce/100 pounds of seed) used for aphid control generally are not effective against Hessian fly. These seed treatments tend to be more effective in the northern portions of the state than they are in the southern portions. They will not provide control of the late winter/spring infestation.

Controlling Hessian fly in susceptible varieties using insecticides after planting is difficult. Other states have had some success using lambdacyhalothrin (Warrior, Karate, and similar products) as a foliar application in late winter. This application must be applied when adults are actively laying eggs and larvae are hatching. Properly timing this application without repeated sampling is difficult. In northern Alabama, the best time to suppress infestation with a foliar spray would most likely be in early to mid March. In southern Alabama, egg laying varies with weather conditions and it may be more difficult to properly time an application without sampling.

Late Winter Scouting for Hessian Flies

Post-Harvest Practices that Spread New Biotypes

Summary of Hessian Fly Management Practices

• Select a Hessian fly resistant variety.

• Plant rye, oats, or a Hessian-fly resistant wheat for grazing.

• If possible, use a tillage method that will bury wheat debris.

• Control volunteer wheat.

• Do not use susceptible wheat for wildlife plantings.

• Avoid continuous planting of wheat in the same field.

• Do not plant wheat before the recommended planting date for your area.

• If a susceptible variety is grown, consider using a systemic seed treatment.

ANR-1069 Revised May 2008. Kathy L. Flanders, Extension Entomologist, Associate Professor, Entomology and Plant Pathology, Auburn University; G. David Buntin, Research Entomologist, Professor, University of Georgia; and Paul L. Mask, Extension Assistant Director, Agriculture, Forestry, and Natural Resources, Auburn University.