Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete. 3 MF-1076 Hessian The Hessian Fly

Understanding its Importance and Management in Production

A lthough the leaves. Seedling wheat seems Hessian fly is often ranked to be preferred. The eggs, as the most important although very tiny, can be seen pest in with the unaided eye and tend production, this small gnat- to resemble wheat leaf rust in like fly and the injury it its early stages. Within three to causes frequently goes H. Leroy Brooks 10 days the reddish, oblong Extension Specialist, Entomology unnoticed. Infestations are eggs will hatch into tiny larvae fairly common in all but the or maggots. This is the stage extreme western and that injures the plant. southwestern portions of the Eggs generally hatch in the state. While seriously evening and larvae migrate damaging losses are downward during the night Extension Entomology currently uncommon in when humidity is high. Larvae Kansas, the insect does cannot survive in the exposed have the capacity to cause devastating detected in Kansas in 1871. During the condition on the leaf surface. The injury to wheat during periods that are first half of the present century, only larvae move downward on the plant favorable for its development. about one out of every four years was between the sheath and the stem and Staggering losses resulting from large designated as being free of serious fly finally stop just above the crown at a multi-county outbreaks have been injury. Infestations have generally been site generally just below the soil experienced several times during the lower during the past 25 to 30 years surface. Larvae feed by withdrawing fly’s 100 year period of existence in and resulting losses have been sap from the plant for a period of eight the state. It is important for growers to relatively modest, although localized to 30 days. The rate of development is recognize that no remedial measures areas of economic damage occur influenced primarily by temperature. are available to save a crop that is somewhere almost every year. Most complete their development presently infested. Proper management before the onset of cold weather. in relation to Hessian fly is therefore Mature larvae are shiny, whitish, similar to the control of most plant Life History legless and headless maggots about diseases; that is to use practices that and Development three-sixteenths inch in length. Full will decrease its ability to survive and During the Fall grown larvae gradually form one- reproduce. Such practices are usually, eighth inch long, brownish, elongated, but not always, compatible with most The adult Hessian fly is a tiny capsule-like cases (puparia) commonly other production objectives. Of the insect about one-eighth inch long, dark called “flaxseeds.” The pass the small grains, wheat is a preferred host; colored, and resembles a gnat in winter as flaxseeds. and may become infested, appearance. On warm days during the Beginning signs of fall infestations but to a lesser extent. fall (September to October), often may or may not be conspicuous. following a rain, these tiny fragile Infested shoots are stunted and emerge and females begin to seek the sometimes killed. The entire stand may Historical Importance young leaves of fall-seeded wheat on The Hessian fly was first observed be lost, especially if heavy infestation which to lay their eggs. The period of occurs shortly after emergence while in New York in 1779 in the vicinity of adult activity is short, flies live for only a Hessian soldier encampment. From the plants are in the seedling stage. If a few days, and during this time, the tillering has begun at the time of there it spread rapidly throughout most females will deposit their eggs in the sections of the U.S. It was first infestation, some plants may be killed grooves on the upper surface of wheat (continued on page 2)

Cooperative Extension Service ¥ Kansas State University ¥ Manhattan Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete. 24

while others survive. Examination of injury may be overcome, but an infested plant will usually reveal an the stem is usually undeveloped central shoot with an weakened resulting in heads unusually broad and thickened dark that are only partially filled green leaf. To confirm the diagnosis, and breakage just above the carefully remove the plant along with infested node. If infestation the roots from the soil and look closely is severe, the stem may be for maggots or flaxseeds by gently killed outright. Low levels pulling the leaf sheath away from the of infestation are not stem and inspecting carefully in the obvious and are frequently crown area. overlooked.

Spring Infestation Supplementary Emergence of adults that produce Broods the spring brood may begin during late The generalized seasonal March, although peak emergence is cycle includes the usually during April. Females prefer occurrence of a main spring young leaf blades for egg deposition. brood, followed by flaxseed Now, the plants are usually jointing, which lie dormant in the much larger and better able to stubble until they emerge to withstand the infestation. The point of produce the main fall brood. "Flaxseed" stage — about 1/8 inch attack by the spring maggots may be at It is important, however, to recognize the base of the plant, below the surface that a portion of the population fail to later than the period of main of the soil, or just above any of the emerge as adults at any one period. infestation, and the point of attack is nodes higher up on the stem. At the Some of the flaxseeds survive in a often higher up on the stems of the point of attack, the tissue of the stem dormant stage for weeks, months or in infested plants. appears to cease growth while the some cases even years. Hence, the surrounding tissue continues to exact source of a given infestation may develop. This forms a niche just large be difficult to document. This also Management Approaches enough for the maggot to lie in. The allows for additional broods 1. How to look for signs of to develop. The presence of infestation. volunteer wheat in or Determining whether a problem adjacent to infested fields exists and its seriousness if present is allow for the development the first step. In the fall, check fields of a summer brood when during late October and November, weather conditions are look for signs of infestations as favorable. The injury on the previously described. Pay particular volunteer is usually of little attention in early planted fields of consequence, but the susceptible varieties. Infestations may individuals arising from be greater in field margins adjacent to this brood, may in turn volunteer or stubble fields. Signs of produce a secondary fall damage early in the spring are not apt brood that is likely to to be obvious unless infestations were produce injury in planted high during the previous fall. Signs of wheat. (Secondary broods spring infestation are best evaluated can develop from other after the wheat is mature just prior to sources as well). Here, harvest. At this time, look mainly for damage is likely even signs of stem breakage. Stems that though the fly-free date was break over just above the node are followed at planting time. particularly suspect. Closely examine An additional brood is also behind the leaf sheath, just below the sometimes observed in the break, for signs of larvae or flaxseed. Adult Hessian Fly — about 1/8 inch long spring. It usually occurs Look also for short undeveloped heads Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete. 35

and tillers that are stunted or dead. it on in greater numbers to the regular help. The risk of fall infestation is Finding some signs of infestation (less crop. Thus, volunteer not only serves to almost always greater where wheat is than 5 percent of stems infested) is not increase the population, it may also planted before the fly-free date and unusual in the eastern two-thirds of the render other practices, such as planting especially during years that are state. Infestations that average less than after the fly-free date, less effective. favorable for fly development. The 10 percent of the stems infested with Keeping volunteer destroyed is also of observance of the fly-free date also is a one flaxseed per stem would probably vital importance in helping to keep useful way to reduce the incidence of result in less than one bushel lost per wheat streak mosaic under control in wheat streak mosaic. The fly-free dates acre; but losses increase rapidly at areas where this disease is of concern. are based on an average time of higher infestation levels and strongly emergence and are the result of signal the need for changes in 5. Plant after the fly-free date. detailed observations made by research production practices. Observing the fly-free date means workers several years ago. As a result, delaying planting until the fly-free date the accuracy of this prediction will 2. Destroy infested stubble. is reached for your location. Waiting vary some from year to year. It may The fly population passes the not always represent the best period following harvest as planting date for optimum yield, flaxseeds in the stubble. but on the average, it correlates Undisturbed stubble will favor the quite well. The fly-free date may survival of the insects. Experience be used locally on a field by field has shown that thorough basis, or during times of concern incorporation of the stubble where it will probably be more effective soil erosion management practices where it is practiced on an area- allow can be a useful technique. wide or community-wide basis. Thorough incorporation must be stressed, however. In one study, 6. Planting too late is also flaxseeds buried one inch below risky. the surface of the soil allowed 26 Growers may be surprised to percent of the population to learn that delaying planting too emerge; at two inches only 6 late in the fall can actually percent emerged and none increase the risk of Hessian fly emerged where the stubble was infestation. While late planting buried to a depth of four inches. In dates do protect the field against another similar study, it was fall infestation, the result is determined that double discing smaller plants in the spring; and was five times more effective than when the spring brood of flies are single discing. active in March or April, those females prefer younger plants for 3. What about burning and Mature Larvae — about 3/16 in length egg laying. Thus, if a source of grazing? infestation is nearby, very late planted Studies have shown that burning until this date allows time for the main wheat of a susceptible variety may will destroy those flaxseeds that are fall brood of adult Hessian flies to suffer extensive damage from spring present on the above-ground portion of emerge and die before the wheat is infestation. the stem. Usually, however, a high planted. Without live wheat plants percentage occur at or below the soil available, the emerging female flies are 7. Resistant varieties — perhaps the line and burning will have little effect deprived on a place to lay their eggs, best answer! on the survival of these individuals. and the grower is therefore able to Often the best answer is to consider The effect from grazing would be avoid fall infestation. There is still planting a resistant variety. Currently, somewhat similar. some risk if a nearby source of our choices are more limited than we infestation exists, and if for some would prefer, yet growers should 4. Destroy volunteer. reason a secondary fall brood develops. consider this option carefully during Volunteer that is allowed to grow Also, observance of the fly-free date times when fly populations appear to for a period of two to three weeks can, does not necessarily prevent the be on the increase. It deserves special especially in wet summers, enable the possibility of spring infestation, consideration where one plans to plant fly to produce an extra brood and carry although in most instances, it should early for fall pasture, and where Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete. 64

usefulness of other options are limited. discussions on varietal performance is A great number of factors must be beyond the scope of this leaflet, thus Acknowledgements: Thanks to Jim considered in making varietal we encourage you to consult with your Hatchett USDA Research Entomologist selections and since our options are county agent for additional information for suggestions and contributions; limited, one factor must be weighed on performance of varieties in your thanks also to Phil Sloderbeck, Don against others in making final locality. In addition, an Extension fact Mock, Bob Bauernfeind and George determinations. A number of varieties sheet, MF-991 should be consulted for Lippert for reviewing and suggesting carry good fly resistance. Detailed the latest information on disease and changes in the final manuscript. Hessian fly ratings.

Cooperative Extension Service, Manhattan, Kansas Issued in furtherance of Cooperative Extension Work, acts of May 8 and June 30, 1914, as amended. Kansas State University, County Extension Councils, and United States Department of Agriculture Cooperating, Richard D. Wootton, Associate Director. All educational programs and materials available without discrimination of the basis of race, color, national origin, sex, age, or disability. Revised August 1993 File Code: Entomology—2, 1-85—5M; 10-85—5M; 8-93—5M