Chemicals ineffective in mealy bug trials

John O'Connell/Capital Press Caribou County, Idaho, dryland grower Sid Cellan shows a plant damaged by barley mealy bugs during a July 28 field day at University of Idaho test plots on his farm.

SODA SPRINGS, Idaho — University of Idaho researchers say insecticide treatments have failed to visibly improve the health of Caribou County dryland grain test plots infested with barley mealy bugs.

Though the trial plots, located in Soda Springs, have not yet been harvested for yield comparisons, plots protected with a seed treatment and plots treated with foliar insecticides applied at herbicide timing appear to be as hard hit by mealy bugs as control plots, said UI Extension cereals pathologist Juliet Marshall.

“The populations are so high I would say they’re overwhelming any control of the insects,” Marshall said.

This season, researchers say mealy bugs, a longtime problem in Caribou County grain, have also exploded in heat- and drought-stressed dryland spring wheat in the Ririe area, where the insects were previously confined mostly to barley.

Mitch Landon, a farm manager in Ririe, had never noticed mealy bugs in his fields before this season.

“It probably was there, but it never was noticeable until this year. Now, it’s like a plague,” said Landon, who failed to control mealy bugs with a citric acid product and will try more summer fallow in the future.

Mealy bugs cause greater yield losses in barley but can also affect wheat, especially spring-planted fields.

UI Extension entomologist Arash Rashed hopes to conduct mealy bug variety trials to test for variety resistance, which thus far hasn’t been documented, starting with greenhouse work this winter.

In a wetter year, Rashed remains hopeful that seed treatments may prove somewhat more effective at controlling the pest. In the future, he’d also like to test foliar treatments applied earlier than herbicide timing.

“Even in the greenhouse, it’s really hard to get mealy bugs because they have this waxy layer, and they’re protected by it,” Rashed said.

Another challenge with controlling mealy bugs is that they live below the soil surface, where foliar insecticides have trouble reaching them.

Caribou County dryland grower Jeff Godfrey said his cousin attempted applying a foliar insecticide with about 20 gallons per ace of water to help the chemical penetrate deep enough to reach the bugs. The approach wasn’t effective, as the water seemed to dilute the chemical, Godfrey said.

“We’ve been experimenting with mustards a little bit, just trying to see if that would be an alternative crop we could use,” Godfrey said. “I haven’t really planted enough mustard to know yet, but I’m sure it’s helping. I’m going to do a little more (mustard) in the rotation.”

Sid Cellan, who owns the fields where the mealy bug trials were conducted, said his northern slopes are moistest but have the most damage from mealy bugs, which like dry conditions. Cellan noted the northern slopes also have the most straw from the previous crop, providing a continuous food source. Cellan believes discing straw into his soil may help in the future. Cellan also plans to try planting Austrian peas as a cover crop — grown only to incorporate into his ground for soil benefits — and to leave about 300 more acres in summer fallow.

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