Grasshoppers should not be a significant threat in Alberta this year, but parts of the province could see higher numbers than they did in 2008.
Alberta’s 2009 grasshopper forecast map predicts a decreased risk of economically significant grasshopper populations throughout the province’s central and southern regions.
However, parts of eastern Alberta along the Saskatchewan border and some parts of the Peace River region may see an elevated risk of damage.
The 2009 map is based on adult grasshopper counts conducted across the province last July and August.
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The counts indicate the number of adult grasshoppers capable of laying eggs.
Scott Meers, an insect management expert with Alberta Agriculture, said weather conditions that occur after the counts can alter the potential risk levels.
“We’re a bit concerned that last fall was a warm, open fall so there was a long egg laying period,” he said.
“That means there is the potential for the grasshopper risk to be higher than forecast (in the maps).”
Meers said a cool, late spring will likely delay the emergence of new grasshoppers, but populations will increase quickly when warm weather arrives.
John Gavloski, an entomologist with Manitoba Agriculture, said provincial grasshopper forecasts are a useful indicator of potential damage, but they do not negate the need for scouting.
Provincial forecasts are presented over a wide geographical area, so localized hot spots often aren’t shown, he added.
“Regardless of what the forecast says, do that early season scouting and if you do get really high populations in a field edge or in an area where they’re concentrated, remember that they’re much easier to deal with when they’re young,” he said.
Adult grasshoppers will lay their eggs in fall in green areas that will offer abundant food for the young insects that emerge the following spring.
Hot spots often include fence lines, ditches and field margins.
Gavloski said scouting should begin in early to mid June, before grasshoppers develop wings and become mobile.
To get an accurate count, producers should peel back the grass and see what’s happening at ground level. Newly hatched grasshoppers will be small, about the size of a wheat kernel, but they are visible to the naked eye.
“They’re not flying yet, so you’re not going to be able to kick the grass and see them flying around,” Gavloski said.
“Later on, when they get bigger, they’re much more mobile and much easier to see so just by kicking around the vegetation, you’ll be able to get an estimate of what the numbers are like.”
Gavloski said getting an accurate estimate of grasshopper numbers is difficult.
“If anyone tells you they can get an accurate grasshopper count, they’re probably lying,” he said.
“Regardless of when you scout, you’re trying to get an estimate. You’re trying to get a gut feeling of whether there’s 10, or two, or 20 grasshoppers per sq. metre.”
Different crops have different economic thresholds for chemical control, but the generally recognized threshold for treatment is eight to 12 insects per sq. metre, Gavloski said.
Timing of application is critical.
If chemicals are applied too early, many eggs won’t have hatched yet and the unhatched eggs will likely result in a second flush of insects.
Conversely, if chemicals are applied too late in the life cycle, grasshoppers will have well developed wings and will disperse over a wide area to escape the chemical.
If grasshoppers are flying, spraying will be required over a much wider area and control efforts will be less effective.
Ideally, spraying should occur when the insects are in the third to fifth instar stage.
At this stage, insects will be too young to fly but they will have small, partially developed wing buds.
Spraying ditches and field edges, rather than entire fields, will probably be sufficient.
“If you do have to control, get them in that mid to late juvenile stage,” Gavloski said. “That’s when you’ll get the best control.”
Grasshopper populations have been increasing gradually over much of Manitoba during the past few years so producers should make scouting a priority.
Producers in southwestern Manitoba should be especially vigilant, as should producers around Brandon, Neepawa and Carman.
Manitoba’s grasshopper forecast map can be viewed on-line at www.gov.mb.ca/agriculture/crops/insects/forecast/grasshopper_interp.html.
Saskatchewan’s map can be viewed at www.agriculture.gov.sk.ca/Default.aspx?DN=b07d649b-9449-42a9-b2ef-30489d2fbde3.
