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Grasshopper risk up in 2009

After lying low for several years, grasshoppers may be making a small but determined comeback in Manitoba.

A Manitoba Agriculture, Food and Rural Initiatives survey predicts pockets of moderate to severe grasshopper infestation in parts of southwestern and south-central Manitoba during 2009.

The most vulnerable area is the extreme southwestern corner of the province where MAFRI lists the risk of infestation as severe to very severe.

Small pockets of potentially severe infestations are located near Carman and in the rural municipality of Rhineland. Moderate infestation is also possible in these areas, as well as southeast of Winnipeg and around Brandon and Neepawa.

MAFRI’s survey is based on adult grasshopper counts in August combined with weather data during the egg-laying period.

Grasshopper populations have recovered a little after staying low for the previous three years. Counts were light in 2005 and 2006, rising slightly in 2007.

This marks the second straight year that grasshopper numbers have increased in agro-Manitoba, said MAFRI entomologist John Gavloski.

Even so, about three-quarters of the surveyed area is rated as light or very light for infestation risk.

And whether or not there’s a grasshopper outbreak depends largely on the weather in spring and early summer, Gavloski said.

Grasshopper eggs normally hatch in late May and early June. Hot, dry weather promotes the hatch while cool, wet conditions suppress it.

The number of eggs laid also depends on the weather. Warm, dry weather in late summer increases grasshoppers’ potential to lay the maximum number of eggs. Frequent rain in August and September restricts their ability to mate and produce egg pods.

Gavloski said very cold weather in winter with little snow cover can kill grasshopper eggs. However, grasshoppers tend to lay eggs in sheltered areas, such as roadsides and the edges of fields, where snow tends to accumulate and insulate them.

Gavloski encouraged farmers to monitor those areas closely in early June to see if emerging grasshopper numbers warrant the need for chemical control.

He said grasshopper counts can run in cycles, with populations building, declining and rebuilding later on.

According to MAFRI, 1999 and 2000 saw low grasshopper counts. Egg counts grew between 2001 and 2003, began falling in 2004, dropped off in 2005 and 2006, then started picking up again in 2007 and 2008.

But there’s nothing to suggest a return to the classic grasshopper plagues of the 1930s, unless conditions become really extreme. Gavloski said modern insecticides have hugely eclipsed insect controls of 70 years ago, when arsenic bait was the only effective weapon. [email protected]

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