'Just a few of those can do enormous damage' to fields
By SEAN ELLIS
Wireworm populations are increasing in Pacific Northwest wheat fields and the pest is causing more damage to cereal crops.
As a result, researchers and the industry have set their sights on the pest, which can increase weed pressure, thin crop stands and decrease yields and profitability.
Wireworms are the larvae of the click beetle. While the beetle is not a pest for cereal grains, the hard, slender, yellowish-white wireworm is.
"Just a few of those can do enormous damage," said Hans Hayden, an Idaho grain grower.
While the pest can't be killed with current recommended insecticide rates, it can be controlled, Washington State University Extension Agronomist Aaron Esser said during a recent webinar sponsored by the Idaho Wheat Commission.
Misdiagnosis of the pest is prevalent and wireworm is common throughout the Pacific Northwest, said Esser, who offered growers who are facing wireworm pressure methods for improving yield and profitability.
His recommendations are based on research conducted at two large on-farm trials in Eastern Washington in dryland conditions that are similar to Eastern Idaho. The trials examined varied rates of Cruiser insecticide and a high labeled rate of Gaucho insecticide.
In both tests, wireworm populations were significantly reduced and profitability significantly increased, Esser said.
Neonicotinoid insecticides are the main way to control wireworm, but they don't actually kill the pests, Esser said. "They are toxic to wireworm but at sublethal doses," he said. "They give them a tummy ache and don't kill them."
For that reason, he said, it's important also to use cultural practices such as delayed planting in the spring if possible, using fallow systems and increasing seeding rates because high plant populations can sustain a greater amount of damage and increase the amount of insecticide that can be used on a per-acre basis.
Putting down fertilizer with seeds also helps plants get a good start and withstand more wireworm damage, he said.
Cultural control methods are underutilized but "go a long way toward helping to minimize wireworm damage," Esser said.
Hayden said using a fallow system helps a lot. "The more annual cropping we do, the worse it seems to get," he said.
Increased weed pressure is one of the telltale signs of wireworm problems, Hayden said.
"If you have a lot of weed problems ... generally it's because you have a wireworm problem," he said. "Wireworm takes wheat out to where (weeds) can grow."
Esser said wireworms are found in most cropping systems in the Pacific Northwest and prefer grass systems. He said the pest's recent increase is due to several factors: cooler, wetter springs, increased cropping intensity, more conservation farming and no longer having the option to use the chemical Lindane, which was banned in agricultural use in 2009.
The webinar presentation, which includes specific insecticide rate recommendations, can be viewed at the Idaho Wheat Commission website at www.idahowheat.org