Hessian fly is typically a bigger problem for wheat growers in the Upper Southeast in the fall than in the spring.
However, a number of growers have reported significant damage from late emerging flies in parts of North Carolina and Virginia this year.
Hessian fly typically has three to six generations per year in the South, with fewer generations in northern latitudes. Generations tend to overlap. The entire life cycle requires about 35 days at 70 degrees F, but takes longer at cool temperatures.
The first generation develops during September or October, depending on latitude and is generally found on volunteer wheat or wild grass hosts.
“I would say for most of the Upper Southeast that volunteer wheat in a double-crop with soybeans is the biggest source and host.
“Hessian fly can certainly harbor on weeds, but our problems are almost entirely from the no-till, continuous wheat-bean scenario,” says Dominic Reisig, North Carolina Extension entomologt.
There are often two more generations in the fall and early winter in Alabama and Georgia, but only one generation during the fall and winter in North Carolina and Virginia.
Wheat growers across the Upper Southeast planted a big crop of wheat last fall and another warm winter presents some challenges to maximize yield and quality of the crop. So far, one of the major challenges in some parts of the region has been managing this late emerging generation of Hessian fly.
With wheat prices holding steady in the $7-8 per bushel range, growers are going to seek maximum yields to take best advantage of the high prices. Unfortunately, the best control for Hessian fly occurred at planting when growers either did or did not plant wheat varieties with genetic resistance to Hessian flies.
The high prices of wheat and the economic advantages of double-cropping wheat and soybeans led many growers to plant extra wheat. With wheat seed supplies in some popular Hessian fly resistant varieties tight in some areas of the region, some growers rolled the dice, hoping for light Hessian fly populations.
Growers in this category are likely in for some tough times, especially if they planted non-resistant varieties earlier than recommended.
Planted in window
“Most of our growers with bad Hessian fly problems got their wheat in within the correct planting window. Generally, we discourage early planting, with late planting helping us miss some of the Hessian fly,” says Reisig.
This year was odd, since a lot of our early wheat missed the fly, while timely-planted wheat was hit. However, based on trapping data on adult flies from previous years, it may not actually be such an odd occurrence.
In Virginia and North Carolina, Hessian flies in damaging numbers have been reported and growers should scout for these pests, especially in early- and late-planted wheat with thin stands.
If pupae are found in thinning wheat, applying a long residual insecticide in March may help, but Reisig says to know your variety before spraying insecticides for Hessian fly control in March.
“Our research indicates fields that have some Hessian fly from the fall generation and are planted with a susceptible variety will not benefit from a spring foliar spray.” And, he adds, all fields with a susceptible variety likely will have Hessian fly at some level.
For some growers along the east coast of North Carolina and southeast Virginia, Hessian flies have already destroyed a few isolated fields of wheat.
Reisig says he recently checked several fields with 50-60 acre spots in Pamlico and Hyde counties, in North Carolina that may be total losses due to Hessian fly damage.
In areas with continuous wheat after soybeans, Hessian fly has been a significant problem, and combined with warm winter weather, can be a real threat to what is shaping up to be a good wheat crop in the Carolinas and Virginia.
Reisig says the majority of the damage from Hessian fly has been on wheat that was planted on time. A heavier than usual egg lay this past fall in some areas of the upper Southeast is a particular concern, he adds.
“I’m worried that parts of North Carolina that don’t normally have problems with Hessian flies may have problems this year,” he says.
Based on early reports of Hessian fly damage, Reisig says it’s important to scout wheat to determine if symptoms regularly seen in wheat fields, like yellowing, lack of vigorous growth, lack of nitrogen or cold weather damage; are being caused by Hessian fly.
To scout for pupae, carefully dig up tillers below the soil and peel back the outer layers of leaves. Often pupae will fall out into the soil or will be feeding on the base of the plant behind these leaves, Reisig says.
“Once you have determined the presence of Hessian fly, you need to make a decision about what to do with your field. Our resistant varieties are still holding up well, so you should focus on fields that are planted with a fairly susceptible variety.
“Then separate your fields with susceptible varieties into three categories independent of planting date,” the North Carolina State entomologist says.
These would be as follows
• Fields that have some Hessian fly from the fall generation and are planted with a susceptible variety.
The vast majority of wheat fields in the upper Southeast fall into this category. These fields will not likely benefit from March insecticide sprays.
• Fields that are moderately infested with Hessian fly from the fall generation and are planted with a susceptible variety.
These fields may benefit from a spring foliar spray, but timing will be critical. Reisig says,
Time spray for mid-March
“Try to time the spray for warm weather in mid-March. You can improve your chances for spray effectiveness by looking at the progression of pupae development. When you squeeze them and they begin to pop pink or red, instead of white, they are close to becoming adults. Remember that we are timing the spray to kill adults, so you should try to hold off your spray until most of the pupae are developed or some have emerged.”
• Fields that are severely infested with Hessian fly from the fall generation and are planted with a susceptible variety.
Unfortunately the best option for some fields will be to till them up. Fields approaching a 100 percent rate of infested tillers with plants that are dying or dead will fall into this category.
Hopefully, a high majority of wheat planted in the Southeast has some built in resistance to Hessian fly. Even so, recent research at Purdue University indicates some resistant varieties are breaking down in the presence of high and repeated populations of Hessian fly.
Although fly populations are suppressed by resistant wheat varieties, the insect has been able to evolve new races (biotypes) that can survive on and injure wheat plants with resistance genes, thus reducing effectiveness on control.
The Purdue-USDA study describes research to determine the frequency of resistance-breaking (virulent) biotypes in Hessian fly populations in the Mid-South and Southeastern U.S. and their response to wheat germplasm lines with 11 resistance genes that are being investigated in the Purdue/USDA program.
Laboratory research identified the major Hessian fly biotypes in 13 populations collected from Arkansas, Georgia, Illinois, North Carolina, and Virginia and determined shifts in virulence to resistance genes in these populations.
Results demonstrated that all genes presently incorporated into soft winter wheat varieties grown in the eastern U.S. are ineffective except in the extreme Southeast.
Newer resistance genes varied in effectiveness to the Hessian fly populations, but 7 of the 11 genes were highly resistant to the populations studied.
This information is vital to researchers developing wheat varieties for the Mid-South and Southeastern states, and will aid entomologists and wheat breeders in determining the most effective way to use resistance genes or gene combinations in the future to prolong their usefulness in controlling the Hessian fly.
(Dominic Reisig reported on the developing problem earlier in the year. For that, see Hessian fly problems apparent in North Carolina wheat.
To keep an eye on the ever-changing insect situation in the North Carolina area, visit his blog site at http://www.nccrops.com/).