Dale Whaley/Washington State University
Winter canola farmers should check their fields for grasshoppers, a Douglas County, Wash., researcher says.
Dale Whaley, extension educator in agronomy for Washington State University in Waterville, recently found a damaged field of winter canola where plants were “severely” defoliated.
“Grasshoppers are voracious predators, they can eat half their body weight per day in forage,” Whaley said.
Farmers should go out and look for damage and the insects themselves using a sweep net, he said.
Farmers may have grasshoppers that have reached an economic threshold, of roughly 7-12 grasshoppers per square meter, Whaley said.
“That’s pretty high pressure,” he said. “That would warrant an action threshold, some kind of a chemical treatment.”
Farmers don’t want to reach the point where the cost of controlling the insects would equal the amount of damage they caused, he said.
A killing frost would kill any mature grasshoppers, but eggs survive in the soil over winter and hatch the following spring, Whaley said.
Grasshoppers typically migrate into the edges of fields, so Whaley recommends farmers start scouting there, where they should see the most damage. If they’re seeing enough damage to warrant pesticide treatment, they may only have to treat borders and not the entire field, he said.
“You can save money by making sure you’re only treating the damaged areas,” he said.
USDA Animal and Plant Health Inspection Service conducts grasshopper surveys throughout Eastern Washington to monitor for grasshopper nymphs in May and then adult insects later in the summer to determine potential for grasshopper outbreaks, said program coordinator George Bruno.
“I’d say in general the grasshopper populations are down overall,” Bruno said. “We always have some isolated outbreaks that occur in any of the 20 counties we survey.”
Most surveys are conducted on rangeland. APHIS doesn’t typically survey crop land, Bruno said, but grasshoppers can easily move in and damage crops adjacent to affected lands.
“Generally, grasshoppers build up for four to five years and reach peak populations where they cause some damage and then, depending on weather, their populations will crash and return to more normal levels,” Bruno said.
Grasshopper numbers reached fairly large outbreaks in recent years, but have returned to more normal levels, he said.
Grasshoppers are common every year, said Karen Sowers, WSU Extension outreach specialist for oilseeds, although this year, farmers saw more green stinkbugs, which don’t appear to cause damage.
Sowers isn’t aware of much damage caused by grasshoppers this year.
“It’s a field-by-field and year-by-year diagnosis,” she said. “That’s the importance of scouting and knowing what the thresholds are for each particular insect. Grasshoppers are the type that tend to move in and move out. They can do a lot of damage in some situations. Always be vigilant, is the number one thing on any of these insects.”