Warm, Dry Weather Means More Grasshoppers

Summer 2010 could see a substantially increased grasshopper risk across the prairies depending on the climate. John Gavloski, an entomologist with Manitoba Agriculture, Food, and Rural Initiatives, gives this message to farmers for 2010: “Be vigilant because if we have favourable conditions for grasshoppers — like dryer and hotter weather — we may see them do more damage than we did last year.”

Scott Hartley, provincial specialist, insect and vertebrate pests with Saskatchewan’s Ministry of Agriculture, says while isolated outbreaks in 2009 lead to some fall stripping of canola pods, and some lentil producers sprayed for grasshoppers (lentils have a much lower threshold than other crops), grasshoppers were not a major issue during the growing season. He notes, though, that in 2009 higher populations were found in northern regions in Alberta and Saskatchewan. Hartley says, “we usually think of grasshoppers as southern pests, but it’s not just a southern thing any more.”

A FINE SEPTEMBER FOR EGG LAYING

Risk forecasts each year are based on fall numbers. Agricultural field-men across the prairies count adult grasshoppers in August. The data from these counts, along with weather projections, go to make up the forecast for the following year. While a wet August prevented grasshoppers from laying eggs, Gavloski says a warm, dry September meant “they were hanging around longer than normal and probably did get to lay a full complement of eggs.” In Saskatchewan, September 2009 was the second warmest on record — making it ideal for egg laying. Hartley believes the western half of province, where conditions were driest, will probably be more susceptible in 2010.

If the warm, dry conditions continue this spring, grasshopper populations could surge; Hartley notes that in 2004, the cool, wet spring resulted in a significant drop in grasshopper numbers. Unfortunately, he also notes, a cool, wet spring isn’t the best for crops either.

IDENTIFY PEST SPECIES

One hundred species of grasshoppers can be found across the prairies but, according to Gavloski, only four of them are actually pests. Grasshoppers do have preferences when it comes to the crops they feed on. They prefer cereals and even have preferences within cereal crops.

SCOUT IN JUNE

June is a critical time for scouting for grasshoppers. Usually they are heavily concentrated around field edges, which makes scouting easier. Gavloski suggests walking an area, for instance the edge of a field or a field, and estimating the number of grasshoppers per square meter. Hartley encourages producers to check out any weedy patches in the field too.

Counting grasshoppers, Gavloski admits, is easier said than done; however, numbers don’t have to be exact. One or two grasshoppers are not a problem (unless the field is planted to lentils whose economic threshold is two grasshoppers per square meter). A heavy infestation will be obvious because grasshoppers will be jumping everywhere.

While more research needs to be done on the economic threshold for different crops, Gavloski provides a rough guideline: for most crops eight to 12 grasshoppers per square meter is the economic threshold. That number can be higher if you’re outside the field in the ditch. For that reason, it’s important not just to measure the edge of a field or a ditch. In some years, Gavloski notes, there has been very little movement of grasshoppers out of the ditches and into the fields.

Gavloski does say that earlier seeding helps alleviate damage because by the time the grasshoppers emerge, the crops are more mature and not as attractive to them. But of course, Gavloski notes, “seeding dates are determined by much more than the emergence of grasshoppers.”

CONTROL AT THIRD INSTAR

For the most part, Hartley says, “It’s a wait and see situation.” Hartley recommends that producers hold off on treatment, Otherwise, farmers have to see something above ground before they can make treatment decisions.

To achieve the most effective control, Hartley advises producers to delay treatment until the grasshoppers reach the third instar, when they are still nymphs and have wingpads instead of wings. By that time the hatch is probably complete. Also, before the third instar, the hoppers are not as mobile and don’t eat as much (though bigger populations can). After the third instar they are more mobile and have bigger appetites and will do more damage.

Gavloski suggests treating before they are adults (after the fifth instar), since they are less mobile. Because they are often concentrated on the edges of the field, one pass around the edge with insecticide may be all that is required. Once they are adults, they have wings and can fly; if they disperse, a farmer may have to spray the whole field.

Insecticide choices are made according to crop. To check, farmers in Saskatchewan can call the Ag-Knowledge Centre in Moose Jaw toll free at 1-866-457-2377 or look online at Saskatchewan’s Guide to Crop Protection www.agriculture.gov.sk.ca/Guide_to_Crop_Protection In Manitoba, farmers can call the nearest MAFRI GO Centre or check the Guide to Crop Protection at www.gov.mb.ca/agriculture/crops/cropproduction/gaa01d01.html

In Alberta, farmers can contact the Ag-Info Centre at 403-310-FARM. Growers can also find information about managing grasshoppers and pictures for identifying them at their province’s ag website.

Hartley encourages farmers to consider insecticide costs as part of their budget. He says, “If things go in favour of the grasshoppers, we will see high numbers and possible economic damage.”

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Patty Milligan is a freelance writer based at Bon Accord, Alta.

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