Experts stress awareness as first line of defense
SAN ANGELO – With the start of the fall wheat planting season only days away, Texas A&M AgriLife Extension Service experts warn of a looming Hessian fly problem facing the future crop.
“Growers and consultants in the Uvalde area report that Hessian fly is an increasing problem in that area,” said Dr. Allen Knutson, AgriLife Extension entomologist at Dallas. “Some fields there were not even harvested this past spring due to Hessian fly damage.”
Dr. David Drake, AgriLife Extension agronomist at San Angelo, said he found high numbers of the pest in demonstration trials near Brady, which prompted both men to believe raising awareness among the region’s wheat growers is warranted.
Knutson said in many cases it’s a little late for producers to implement integrated pest management strategies this season, but since the pest has been on the increase in recent years, current awareness is key to its future management.
“Warm winters, higher rainfall in recent years, along with the increased use of minimum tillage farming practices and the lack of controlling volunteer wheat sprouting from grain dropped from a previous crop, are all contributing to the problem,” Knutson said.
Hessian fly larvae feed on the wheat stem beneath the leaf sheath consuming the resulting plant sap that bleeds from the injured stem, Drake said.
“Infestations stunt the plant’s growth in the fall, potentially limiting its forage production for livestock,” Drake said. “Infestations in the spring stunt tiller growth, reducing grain yields and can cause lodging or stem breakage, making it difficult or impossible to harvest.“
Knutson said current conditions indicate the fly may be a greater threat from both a crop damage standpoint and over many more acres of wheat in South and West Central Texas this fall.
“Hessian fly damage has been increasing in recent years and given the high populations in some areas, preventive practices to reduce risk of crop loss will be especially important,“ Knutson said. “Hessian fly is able to continue to reproduce during mild winters, resulting in higher infestations in early spring. Higher rainfall and humidity, such as we are seeing over much of the state now, ensure a high survival of the pests’ larvae into the fall and following spring.”
Both men stressed that once a planted field is infested with Hessian fly, there is little a grower can do to protect the crop.
“Effective management depends on preventive measures,” Knutson said. “Eliminating volunteer wheat in the early fall is especially important, as early emerging Hessian flies can reproduce in volunteer wheat and later move to the fall- or spring-planted wheat crop once it starts to grow. Although they are weak fliers, the tiny adult flies can be carried on the wind from volunteer wheat or early planted wheat to adjacent wheat fields.”
Drake said volunteer wheat is also a source of other wheat diseases and insect pests, including wheat curl mites that transmit wheat streak mosaic virus, often another serious source of yield loss in wheat.
“Simply destroying volunteer wheat two to three weeks before planting the wheat crop can save the producer much grief by reducing the instances of a number of wheat pests, not the least of which is Hessian fly,” Drake said.
Selecting the right wheat variety is another means of defense, Knutson said
“Planting wheat varieties with genetic resistance to Hessian fly can also be effective in controlling this pest and should be the growers’ first line of defense after the destruction of volunteer wheat,” he said.
He warned though that Hessian fly biotypes that do survive on a specific variety, even a resistant variety, can increase in number if that same variety is grown year after year across a region.
“For this reason, it may be necessary to change to wheat varieties that have shown resistance to biotypes currently present in a given area,” he said. “Unfortunately, it may be hard to find an adapted wheat variety that yields well and also has resistance to Hessian fly. As an example, some promising varieties with Hessian fly resistance didn’t vernalize in 2015-16. They did not receive the amount of cold weather necessary to produce a grain crop during last season’s mild winter in South Texas.”
A list of wheat varieties that Drake said have been evaluated by Texas A&M for yield, adaptability and level of pest resistance, including Hessian fly, is available at: http://varietytesting.tamu.edu/wheat .
Seed treatment insecticides are the third line of defense Knutson recommends.
“The insecticides Cruiser, Gaucho and Nipslt Inside are formulated to be applied to the wheat seed. As the seed sprouts, the insecticide is picked up by the roots and moved systemically within the wheat seedling,” he said. “Seed treatments can reduce infestation of Hessian fly for several weeks after planting, but do not last long enough to stop infestations from later generations. Seed treatments are especially important when Hessian fly-susceptible varieties are planted and when wheat is planted early for grazing purposes.”
Drake said delaying planting until the arrival of cooler fall temperatures can also reduce Hessian fly infestation and survival, which also holds true for fall armyworms, another early season pest of wheat.
Knutson said Hessian fly survives through the summer as inactive, non-feeding puparia in what is called the “flaxseed stage” in the residue of the previous wheat crop. Plowing the old crop stubble and volunteer wheat under to a depth of 4 to 6 inches before late August will reduce emergence of adult flies.
“Although minimum tillage has a number of advantages, when it comes to wheat, it probably increases Hessian fly survival as the crop residue containing over-summering Hessian fly puparia is not buried,” he said.
Knutson said crop rotation is the final step in limiting damage from the pest.
“Where wheat has been planted for a number of years, crop rotation can help reduce the risk of Hessian fly outbreaks within that field,” he said. “Burning straw is of limited value, as it only kills the puparia above the soil while those below the soil line survive. So we don’t recommend burning as a control practice for Hessian fly.
“If current conditions continue through the fall and winter, this could be a bad year for Hessian fly damage on what could otherwise be a promising wheat crop across West Central and South Texas,” Knutson said. “So cultural practices including destruction of volunteer wheat, burying crop residue, planting resistant varieties and insecticide seed treatments will be more important now than ever to reduce the risk of Hessian fly damage to the coming year’s wheat crop.”
For more on Hessian fly, see http://agrilife.org/texasrowcrops/2016/06/07/managing-for-hessian-fly-in-texas-wheat/