1. Tyler Mays, Extension Agent-IPM, Hill and McLennan Counties

David R. Drake, Extension Agent-IPM, District 4 – Commerce, TX Email: drdrake@ag.tamu.edu

Matt Matocha, Extension Program Specialist- IPM,  Southern Blacklands, Thrall, TX, matthew.matocha@ag.tamu.edu

Hessian fly are being found in wheat fields across the Texas Blacklands and are a potential production issue this year. The Hessian fly is a small fly that during the larval stage can be a significant pest of wheat and some other small grain crops like barley, triticale, and rye. There are several wild host plant species for the Hessian fly including quackgrass, western wheatgrass, goatgrass, timothy, and various other wild grasses. The larvae are cigar shaped with a creamy white body that has a green streak down the middle of its back (Figure 1). After feeding for some time the larva forms a puparium which ranges in color from dark brown to black and resembles a flaxseed (Figure 2). A single generation of the Hessian fly can be completed in 40 to 50 days, but adults from a single generation do not emerge all at once and can survive in the puparium for upwards of four months before emerging.

Figure 1. Hessian fly larvae infesting a wheat tiller. Photo credit: D. Tyler Mays, Texas A&M AgriLife Extension

Figure 2. Hessian fly Puparia on a wheat tiller. Photo credit: D. Tyler Mays, Texas A&M AgriLife Extension.

The adult female lays her eggs on the leaf surface between the leaf veins, and the eggs are small, elongated, and red to orange in color. The eggs can hatch within 3-10 days depending on temperature, and at this time the larvae are red to orange in color and follow the leaf surface to move between the leaf sheath and stem setting up feeding sites in the crown of the plant, or just above the node on jointed wheat. After a feeding site is established, the larva develops its characteristic white color, and will not move from that site until it emerges as an adult. The extent of the damage caused by Hessian fly is dependent on when the infestation occurs, the level of infestation, and if the variety is resistant to the Hessian fly biotypes present in the area. Common damage symptoms characteristic of a Hessian fly infestation include: death of young tillers, stunting, and lodging. Research conducted in Georgia indicated that significant yield loss can be observed when 5-8 percent of tillers are infested in the fall, or when13-20 percent of tillers are infested in the spring (Buntin, 1999). This data also indicated that for every 10 percent of plants infested a yield loss of 1 bushel per acre can be expected. More recent data conducted by a graduate student at Oklahoma State University has found that 5 bushel per acre yield loss when a field averages 1 Hessian fly per tiller, and about a 35-bushel loss when the field averages 9 Hessian fly per tiller (Alvey et al., 2009). This data set showed a negative correlation between the number of Hessian fly per tiller and grain yield (Figure 3).

Currently, after looking at several fields in the Central Blacklands area experiencing the most Hessian fly issues, the number of Hessian fly per tiller are below damage threshold and seeing a significant yield loss may not occur. However, since we know Hessian fly are present and can expect to see more generations of Hessian fly to emerge this spring, as temperatures stay warm, fields could easily be infested to a level of seeing economic loss, especially from lodging.  As with all crop losses, the extent and risk of loss is influenced by present and future crop conditions and the amount of prevention practices used.

Figure 3. Relationship between the number of Hessian fly per tiller and wheat yield (Alvey et al., 2009).

MANAGEMENT OPTIONS:

Hessian fly management options are limited to only preventative practices. Insecticides applied after the crop is emerged and growing will not control Hessian fly once they enter the area between the leaf sheath and stem, as no insecticide can get to where they are located. Some people have questioned the use of pyrethroid insecticides to control the adults and although the adult is susceptible to this insecticide this is not a recommended management practice as timing adult emergence is extremely difficult, and because adults emerge through the growing season multiple applications would be needed. Additionally, the use of pyrethroid based insecticides will wipe out any beneficial insect in the field and could lead to an outbreak of other insect pest like aphids which can then transmit the barley yellow dwarf virus. Current management options for Hessian fly include crop rotation, tillage, managing volunteer wheat, planting resistant varieties, later planting, and using insecticide seed treatments. Crop rotation is the first line of defense against Hessian fly along with several other insect and fungal pests. When you rotate away from wheat or other suitable host like barley, triticale, or rye you reduce sites for the Hessian fly population to survive on before another susceptible host plant is planted. Managing volunteer wheat during fallow periods is also an important aspect of Hessian fly management as volunteer wheat can be an excellent food source for the Hessian fly to build up numbers that can infest the next wheat crop. Implementing tillage practices can also help reduce the Hessian fly pressure for subsequent years. This is because the Hessian fly survive in infested crop residue as a puparium and when buried beneath the soil surface it is hard for the small fly to emerge and lay eggs. Selecting a variety that is resistant to the Hessian fly is also an important management practice, as even though you implement crop rotation, volunteer management, and tillage there will still be Hessian fly present in the environment that can cause damage. By planting a variety with resistance, you limit the amount of Hessian fly that can infest the plants, and the plant will tolerate Hessian fly feeding better than a variety without any resistance to Hessian fly. Delaying planting can also be used to potentially reduce issues with fall infestations, however, unlike states farther north; Texas does not have suggested “fly free” planting dates and can still be warm later than agronomically suggested wheat planting dates.  The last management option is to treat seed with an insecticide seed treatment prior to planting. There are three insecticide seed treatments that can be used on wheat, Cruiser, Poncho, and Gaucho. By using an insecticide seed treatment, you will not eliminate Hessian fly infestations, but you will control Hessian fly infestations for about 21-30 days after planting. By using the seed treatment, you will prevent Hessian fly infestations from occurring during the stand establishment stage of wheat production, but after the seed treatment wears off Hessian fly will be able to successfully infest tillers. Data from Texas A&M AgriLife Research has seen a significant reduction in percent tillers infested with Hessian Fly when seed was treated with Gaucho, and a slight increase was observed between the insecticide seed treatments and the untreated control (Figure 4).

Figure 4. Impact of various rates of Gaucho Insecticide Seed Treatment on Hessian Fly infestation and Yield.

WHAT SHOULD I DO?

With the reports of Hessian fly being found across Central Texas, in particularly the Southern Blacklands around Taylor, it is recommended to scout fields for Hessian fly, especially if you do not know if your variety is resistant or if the variety is susceptible. Table 1 below show the Hessian fly resistance rating for some of the most common wheat varieties planted in the Blacklands. The 2021 Texas Wheat Variety Trial Results available at http://varietytesting.tamu.edu; also lists the most recent Hessian fly resistance ratings for classes of wheat grown in Texas. Scouting for Hessian fly is a time consuming and tedious process that involves digging plants up and inspecting between the leaf sheath and stem for larvae or puparia. Depending on field size at least 100 tillers from different areas of the field should be inspected for Hessian fly. If infestation is high, the field should be evaluated the same way you would for winter kill and decide on if you need to terminate the crop to plant a second crop on the field or if you want to keep the wheat crop to harvest for either forage or grain. The fields Matt Matocha and Tyler Mays looked at last week in the Taylor area, did not have enough Hessian fly per tiller to cause yield concerns, and did not see enough dead tillers to justify terminating the wheat crop. Hessian flys are present in Northeast Texas but also not at high levels. Additionally, we are still early in the wheat production year, and there is still some time left for plants to set new tillers that can contribute to yield. If your field(s) have a Hessian fly issue it is highly recommended that you rotate that field away from wheat or other suitable small grain crop for at least one season. Additionally, in these fields, once harvest operations are complete, tillage should be used to bury the crop residue to at least two inches deep, and any volunteer wheat should be controlled to limit the number of plants in the area for Hessian fly populations to sustain and build on over the summer and into the fall months. If you have a field that is going to be planted to wheat for the 2022-2023 growing season and it is near a field that is experiencing Hessian fly issues it is recommended to plant those fields with a variety that is resistant to Hessian fly. Using insecticide seed treatment and delaying planting until cooler weather should also provide some protection.

References

Alvey, D.R. 2009. Evaluation of the Impact of Hessian Fly (Mayetiola destructor) on Oklahoma Winter Wheat Systems. M.S. Oklahoma State University. Retrieved from https://shareok.org/handle/11244/8985

Buntin, G. D. 1999. Hessian fly (Diptera: Cecidomyiidae) injury and loss of winter wheat grain yield and quality. J. Econ. Entomol. 92:1190–1197.