Courtesy Arash Rashed
ABERDEEN, Idaho — University of Idaho and Washington State University researchers have been encouraged by results of studies in both states using beneficial fungus and nematode species to improve wheat survival and yield in wireworm-infested soils.
The researchers say farmers are limited in both the availability and effectiveness of chemicals labeled to fight wireworms, and new tools will be needed to help control the destructive pest.
Aaron Esser, WSU Extension director for Adams County, and WSU entomologist David Crowder conducted outdoor trials in two fields in 2016 and repeated the experiment in two more fields this season, using commercially available fungus and nematode species known to attack wireworms.
UI Extension entomologist Arash Rashed conducted a similar study this season with the same species of fungus and nematode inside of greenhouses at the UI Aberdeen Research & Extension Center. Rashed also added a treatment with diatomaceous earth — a powder form of a siliceous sedimentary rock known to cut the surface cuticles of insects, causing them to lose moisture. The projects received grant funding from USDA’s National Institute of Food and Agriculture.
“Usually biological control agents are not expected to completely replace pesticides and provide the same level of protection,” Rashed said, adding more research is needed to determine how common pesticides interact with his experimental treatments. “Our hope is to obtain an additional tool to employ in integrated pest management of wireworms.”
Esser said during its field trials in 2016 and this season, WSU planted soft white spring wheat in one field with a moderate wireworm infestation and another with heavy pressure. In 24-foot by 6-foot plots, they tested five different treatments in four replications including a control, varying levels of beneficial nematodes or fungus and combinations of the two.
In one field this season, Esser said the controlled check with no wireworm treatment yielded 51 bushels of wheat per acre, compared with 54 to 55 bushels per acre from either nematode or fungus treatments and 56 bushels per acre from a combination of the two biological controls. By comparison, applying 2 ounces of the leading wireworm pesticide, Goucho, resulted in 62 bushels per acre. Esser said the experiment generated similar results last season.
“We’re still trying to figure out if the nematode or the fungus is the better option,” Esser said. “Both organisms aren’t that easy to work with.”
Rashed conducted his greenhouse study last spring and repeated it again in the early summer. His treatments included a control, solo doses of diatomaceous earth and beneficial nematodes and fungi and combinations of the three. He evaluated the performance of potted wheat plants in wireworm-infested sandy and peat moss-enhanced soils.
Rashed saw little difference in plant biomass among treatments in soil with peat moss, which he believes enabled plants to withstand wireworm damage. But he noticed a relative improvement in plant biomass from the addition of beneficial nematodes and fungi.
“The initial analysis suggests the combination of the beneficial fungus and nematode, with or without (diatomaceous earth), may reduce the percent damage relative to other treatments,” Rashed said, adding additional research is needed.
Rashed said the tools could be useful in organic production, and he’d like to study if the treatments can persist in soil for several seasons, which would make them more cost effective.