G. David Buntin, University of Georgia, Grain Crop Entomologist
The Hessian fly, Mayetiola destructor, can cause severe damage to wheat production throughout the southern United States. In spring of 2023, we had a serious outbreak of Hessian fly in wheat across the southern United States and Coastal Plain region of Georgia. Infestations varied but it has been over a decade since the last outbreak of this pest in winter wheat in Georgia. Wheat is the primary host of the Hessian fly, but it also can attack triticale, barley, and rye. The Hessian fly does not attack oats and ryegrass. The only important non-crop host in Georgia is little barley.
Adult Hessian flies are small black flies about the size of a mosquito. Adults live about two days and females lay about 200 eggs in the grooves of the upper side of the wheat leaves. The eggs are orangered, 1/32 inch long and hatch in 3 to 5 days. Young reddish larvae move along a leaf groove to the leaf sheath and then move between the leaf sheath and stem where they feed on the stem above the leaf base. Maggots become white after molting and appear greenish white when fully grown. Once larvae move to the stem base, they are protected from weather extremes and foliar-applied insecticides.
Maggots suck sap and stunt tillers presumably by injecting a toxin into the plant. Infested jointed stems are shortened and weakened at the joint where feeding occurs. Grain filling of infested stems is reduced and damaged stems may lodge before harvest. Usually, three generations occur in the Piedmont region and four generations occur in the Coastal Plain region of Georgia. The fall and winter generations stunt and kill seedling plants and vegetative tillers. The spring generation infests jointed stems during head emergence and grain filling. Yield losses usually occur when fall tiller infestations exceed 8% of tillers and when spring stem infestations exceed 15% of stems.
The Hessian fly is a cool season insect and is dormant over the summer in wheat stubble as a puparium, which is sometimes called a ‘flaxseed’. Adults begin to emerge in early September as soil temperatures decline. Since wheat is not yet planted, the first generation develops in volunteer small grains and little barley. Thus, reduced tillage, lack of crop rotation (wheat after wheat), and lack of volunteer wheat control in summer crops enhance problems with Hessian fly in autumn. Burning wheat stubble alone does not control over summering puparia but will make disk tillage more effective at burying puparia before fall emergence.
Planting a Hessian fly-resistant variety is the most effective way to control Hessian fly.
The following table is the list of wheat and triticale varieties recommended by the UGA Small Grains Commodity Team for production in Georgia for 2023-2024 season. The letter after the variety name indicates adaptation as S = statewide, P = piedmont region and C = coastal plain region. I have highlighted varieties based on the level of resistance to Hessian fly as yellow indicates good resistance, blue indicates fair resistance, and white or no highlighting are susceptible to the Hessian fly. Ratings are based on several years of data where generally good is 0 – 10% infested plants, fair is 11 -20% infested plants, and poor is greater than 20% infested plants.
All varieties in the Georgia state wheat variety trials are evaluated for Hessian fly resistance each year. A complete list is in Table 3 at the end of this document and in the 2022-2023 Small Grain Performance Tests Bulletin at https://swvt.uga.edu/ (click on the Winter Grains and Forages, 2023 report, pages 22-23).