Farmers in Alberta and Saskatchewan could see grasshopper infestations this year. But before spraying, make sure the hoppers in your crop are actually pests
Of the 80 grasshopper species on the prairies, only a few are pests. Some non-pests will eat weeds, including kochia, Russian thistle, and ragweed. The two-striped, Packard’s, lesser migratory and clear-winged grasshoppers are the most common grasshopper pests on the Prairies.
“If it’s flying in the spring, it’s not a major pest species. If it’s singing, it’s not a major pest species. If it has coloured wings, it’s not a pest,” says Harry Brook, crop specialist with Alberta Agriculture and Rural Development. “If you’re out scouting and you see grasshoppers, you need to be able to identify them to make sure you’ve got the right species.”
Each August, field staff count adult grasshoppers. Based on these numbers, Alberta Agriculture creates a grasshopper forecast map that shows areas that may have grasshopper problems the following growing season. The 2012 forecast shows severe or very severe risk zones in Alberta’s Peace and northern regions. Central and southern Alberta also have some severe risk zones. In Saskatchewan, the Meadow Lake and southwest areas have the highest risk for infestations in 2012. Most of Manitoba is forecasted to be very low risk for this year.
“Even if you’re in a green area, where it looks like there won’t be many, you’ve still got to check. You’re more likely to have a problem in those areas with higher numbers. But that doesn’t mean you’re free and clear in the other (areas),” says Brook.
Brook recommends scouting regularly throughout the growing season. Grasshoppers lay their eggs in the fall on undisturbed soil, traditionally found at the field edges. However, from farmers who practice zero-till, Brook has heard that grasshoppers may lay their eggs throughout the field. Brook also suggests checking south-facing slopes first, as the grasshoppers may hatch first there.
Environmental and biological conditions often keep grasshopper populations in check. Wet conditions can drown newly emerged grasshoppers. Danyk flies will pounce on grasshoppers to deposit maggots, which eat the grasshoppers from the inside. Like a scene from a horror film, the maggot eventually emerges from the grasshopper’s neck. Grasshoppers are also vulnerable to a fungus that forces them to climb a high piece of vegetation. The grasshopper dies while clinging to the plant and spreads spores to other grasshoppers.
When to spray
Once grasshopper populations reach economic levels, farmers need to consider spraying. Brook suggests an economic threshold of about 18 grasshoppers per square metre. Younger crops, or crops under heat stress, are more vulnerable to grasshopper damage.
Timing is crucial to effectively treating problem grasshoppers. Farmers who spray when grasshoppers first emerge will miss the unhatched grasshoppers, which may make up the bulk of the population. Dan Johnson has written a grasshopper identification and control guide for the Saskatchewan Pulse Growers and Agriculture and Agri-Food Canada. Johnson suggests considering control methods only once the grasshoppers start feeding and look like they will cause significant damage.
But waiting until the grasshoppers are fully mature isn’t recommended either.
“The later you wait, actually, the less effective are the insecticides you’re using, and the more mobile the bugs become. Once they become adults, you’re really stuffed because you can spray them all out, but even if you have an effective chemical, they’ve got wings,” says Brook. He recommends spraying once the grasshoppers are about a quarter-inch long.
Whether or not the neighbours are spraying can also affect application effectiveness. “There’s nothing more frustrating than spraying your grasshoppers, and then they come off the neighbour’s property onto yours. So you spray them again. Then they come in off the neighbour’s property and you spray them again. Sooner or later you’ve got to say ‘enough’s enough,’” says Brook.
Chemicals registered to control grasshoppers include Decis, Dibrom, Ecobran, Malathion, Matador/Silencer, Monitor, Sevin XLR, Cygon/Lagon, Ripcord and the chlorpyrifos group. Not all chemicals are registered to control grasshoppers on all crops. See provincial crop protection guides for details.
Johnson’s grasshopper control and identification guide is available through the Saskatchewan Pulse Growers’ website (search for “grasshoppers” at www.saskpulse.com). The guide contains more detailed information on identifying grasshopper species, as well as cultural control methods. †