HANDY GRASSHOPPER BOOKLET
Agriculture and Agri-Food Canada and Saskatchewan Pulse Growers have a handy new booklet called “Grasshopper identification and control methods.” Dan Johnson at the research centre in Lethbridge developed the booklet with funding support from Saskatchewan Pulse Growers.
Grainews has a PDF version of the book we can email to you. Saskatchewan Pulse Growers has printed copies. To get one, call Jennifer at the SPG office at 306-668-0350 or email [email protected]
Grasshopper populations are set to increase in 2009 over 2008 based on counts of egg-laying adults last fall. But even if spring and summer conditions are warm and dry — which favours an early hatch and rapid growth — Scott Hartley, provincial insect management specialist with Saskatchewan Ministry of Agriculture, does not expect a repeat of 2003. The egg-laying population just wasn’t high enough last fall to produce a population big enough to reach economic control threshold across a broad section of the Prairies, he says. Lots of Saskatchewan and Alberta farms face virtually no threat at all.
But there will be hot spots, as usual. Manitoba counts reached “very severe” levels in the extreme southwest and “severe” levels in a few quite large areas, again in the southwest and around Neepawa and Carman.
Population spikes in Saskatchewan were recorded around Southey and Elrose, with moderate numbers in the southeast. Highest counts for Alberta were all along the Saskatchewan border. Growers within the orange, pink and red areas of the map should pay closer attention to grasshopper feeding.
“Moderate infestations of eight to 12 grasshoppers per square metre can represent a risk to most annual crops,” says a Saskatchewan Ministry of Agriculture forecast map report. The report also reminds farmers that the economic threshold, the pest population at which control measures are cost effective, is lowered as commodity prices rise.
WHAT TO WA TCH FOR
Monitoring should start in May. Grasshoppers tend to lay their eggs in fencelines and shelterbelts — areas where grasses are left to grow all year — and they’ll move into a field from there. Monitor these areas first. If you see severe numbers here, you will want to check your fields.
Grasshoppers go through five instar phases before they become flying adults. By the time the first-hatched have reached the third instar stage, most of the eggs that will have hatched. “At that point, you’ll know the population you’re dealing with,” Hartley says.
The flying adults are bigger and can cover more area, and therefore cause more damage. But you can get economic-level losses from instars if the numbers are high enough, says Dan Johnson, entomologist and grassland scientist at the University of Lethbridge. Instars walk through a crop from field edges, so they’re fairly easy to scout. If you see instars feeding along a field edge, a targeted spray along that field edge may be enough.
But don’t get too hasty. Johnson says holding back doesn’t hurt. “It’s better to be a little late. That way you get more of them.”
Rather than focus on the number of grasshoppers, the better plan is to watch for plant damage. Johnson says high numbers alone are not enough to warrant a spray. “Species, weather and crop type are all factors in how much economic damage you’ll get,” he says. “We often use a general threshold of 10 per square metre, but I’ve seen way higher numbers that cause no damage and much lower numbers that can cause big losses.”
As an example, Hartley says the thresholds are very low for flax and lentils. That’s because grasshoppers will go right after the moneymaker in these crops — the green flax bolls and the new lentil pods. Just two adults per square metre are enough to warrant a spray. But again, look for damage. If they’re not feeding, you don’t need to spray them.
A number of insecticide sprays are registered for grasshoppers. Before you spray, the Saskatchewan Ministry of Agriculture forecast report provides this reminder: “Most insecticides have broad spectrum activity and can be fatal to beneficial insects such as honey bees, other pollinators and parasitic insects capable of natural biological control, as well as pest species.”
Bees do more than just make honey. They are pollinators for many crops, garden plants and wild species. The report gives these strategies to avoid a negative impact on bees:
Avoid spraying or allowing spray to drift onto flowering crops or weeds where honey bees are foraging.
Spray in the late evening or early morning when the bees are not flying.
Contact local beekeepers to provide a few days warning of spraying intentions.
Keep in mind that the objective is to sensibly control grasshopper populations to protect the crop. One hundred per cent elimination of the insect is not a realistic goal.
Jay Whetter is the editor of Grainews.