For the most part, Saskatchewan farmers are unlikely to be fighting waves of grasshoppers this year, according to Saskatchewan Agriculture’s 2014 hopper forecast.
But Saskatchewan’s 2014 forecast does show one bull’s eye of severe risk.
“And in the middle of that bull’s eye is Meadow Lake,” Peter Walsh told farmers at Cavalier Agrow’s farm forum in North Battleford this April. Walsh teaches courses in insect, weed and disease management, along with crop agronomy, at Lakeland College in Vermilion.
A count of at least 12 adult hoppers per square metre in the fall adds up to a severe risk forecast the following year.
Meadow Lake farmers aren’t the only Prairie producers likely to suffer hopper plagues this year. Alberta Agriculture and Rural Development’s forecast shows very severe risk (more than 24 hoppers found per square metre) near Grande Prairie, along with areas in the northeast and west-central regions.
Farmers in zones not rated as high risk aren’t necessarily going to get off scot-free this year, though.
Forecasts partly depend on weather and natural enemies, Dr. John Gavloski, entomologist with Manitoba Agriculture, Food and Rural Development, said in an interview. And local populations can vary.
“We try to do our best to make sure that the counts are representative, but that’s not always the case,” said Gavloski.
Not all grasshoppers are crop killers and it’s well worth knowing which are friend and which are foe.
Manitobans walking the ditches might see bright green insects resembling grasshoppers. They are katydids, Gavloski said. “They’ll never move in and damage the crop.”
Both Gavloski and Walsh cited the Russian Thistle Grasshopper as a species that only eats weeds.
But farmers don’t have to be able to name the specific specie to know if a hopper will gorge itself on grain. Any grasshopper that makes a clacking noise while flying, has colourful wings (yellow or rose-coloured), or is flying in April or May is not a pest, Walsh told farmers.
“All of our pest species over-winter as eggs. That’s why in June they’re just hatching out,” said Gavloski. Pest species usually aren’t adults until July.
But some non-pest species over-winter, said Gavloski. “So they’re nearly mature early in the season.”
Females that are common pests will lay eggs in the fall “until the frost shuts her down,” said Walsh.
Nymphs emerge and begin feeding immediately, Walsh added. “The grasshopper does not have a resting stage. There is no stage in the hopper like a cocoon.”
Scouting and thresholds
Alberta Agriculture and Rural Development’s website recommends checking field edges, fence lines and ditches for grasshoppers. Egg beds generally line field edges so instars will be found there first.
To count grasshoppers, Manitoba Agriculture’s site suggests starting in one field corner, walking diagonally past the centre, and then walking straight out to one side of the field. While walking, note how many nymphs jump from a square foot area.
The ministry suggests taking at least 20 of these counts per survey. Dividing the total by two will give an approximate number of hoppers per square metre.
The economic threshold for grasshoppers is eight to 12 hoppers per square metre, according to Manitoba Ag’s site. Gavloski said this threshold is nominal, meaning there isn’t quantitative data correlating insect damage to yield loss.
“It’s basically a best guess of what people think is likely economical,” he said.
Farmers with lower-value crops should err on the high end of the economic threshold, Gavloski said. But for high-value crops, action is needed when grasshoppers breach the lower end of the spectrum, he added.
And crops such as lentils and flax likely require action before the grasshoppers hit the low end of the threshold. In fact, lentils at the flowering and podding stage have a recommended threshold of two hoppers per square metre.
Soybeans and canola aren’t preferred snacks for most hoppers, but there are species that will eat them once their preferred food sources dry down, Gavloski said.
“Cereal crops are favoured by some of our pest species, so they’re certainly more vulnerable,” said Gavloski.
Gavloski suggested controlling hoppers at roughly the third or fourth instar stage, before they start damaging crops.
“Adult grasshoppers are much harder to control than juveniles,” said Gavloski. “And the juveniles are often concentrated along field edges and borders.”
Walsh also recommended farmers delay spraying until nymphs hit the third instar. At that stage they’ll have small wing pads.
“What you’re waiting for is the complete hatch. If you jump the gun the first time you see those little nymphs out there, you may have to spray a second time,” said Walsh.
But farmers will need to weigh this advice against how much damage is already being done to the crop and the crop type, said Walsh. Grasses, such as wheat, will outgrow some of the early damage, Walsh added.
“And if I’m still waiting for the rest of the hatch, I probably don’t have peas or canola into bud or any kind of stage like that,” Walsh said.
It ultimately comes down to individual farmers’ risk tolerance, Walsh said. “Where’s your line? Everybody’s got their line. And just some cautions that if you can hold off a bit, you may only have to spray once.”
Common wisdom says that a wet spring is hard on newly-hatched hoppers, but spring rains don’t always drown grasshoppers.
Instars “breathe through their abdomens. And they can’t lift their abdomens out of the muck and the mud and the water,” Walsh explained.
But wet weather doesn’t affect the eggs, so whether or not spring rains kill instars comes down to timing.
“Heavy rains in June could potentially kill lots of grasshoppers. Heavy rains in April will do next to nothing,” said Gavloski.
And a cold spring will delay the hatch, and so if the wet weather passes, the eggs will still be viable, said Walsh.