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Weather Vs Insects 2010

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alberta farmer | stettler

There’s an old Prairie saying that three things always go together – drought, grasshoppers and tight money.”

Money may not be so tight right now but but the first two seem set to continue their old partnership, and grasshopper populations are on the rise in many areas of the province. Large numbers are expected in the Peace and in the central area around Lacombe.

“We are set up for big problems in those areas. What happens in May will tell the story,” says Scott Meers, an Alberta Agriculture insect-management specialist in Brooks.

Meers told a meeting here that heavy rainfalls in May would cut down on the emerging grasshopper populations, but hot dry conditions will mean potential for serious outbreaks.

Areas north of Calgary and around Lethbridge saw a resurgence in grasshoppers last year. New species are contributing to the larger numbers, including the red-legged grasshopper, the northern grasshopper and Dawson’s grasshopper.

Pea leaf weevil increase

Meers said the pea leaf weevil, a relatively new pest in the province, has been in the increase since 2008. Warm spring weather is essential for the pea leaf weevil to move into fields and populations decrease in drier years because the larvae go down into the soil, pupate and get stranded inside the soil in dry weather.

New-generation adults emerge in August, lay their eggs and then overwinter as adults. “We’re seeing them overwinter in alfalfa and in the headlands,” said Meers.

Pea leaf weevils can easily find isolated fields as they are good fliers, and only fly when temperatures reach above 15 C. They are the most destructive in the larval stage since they consume root nodules by hollowing them out. This results in reduced yield of pea crops due to denitrification. The adult insects, who are difficult to find in the fields, are not as much of an economic threat. The pea leaf weevil’s territory includes the areas around Lethbridge, Medicine Hat, Vulcan and Olds.

Meers said seed treatments can combat this insect and have proven consistently beneficial. Foliar treatments are also available, but researchers have yet to see economic returns from using them, he said.

Midge on decline

Meers said wheat midge has been declining for the past two years despite an infestation in Wheatland County. However, the insects have recently been found throughout the irrigated areas in southern Alberta and could become an economic concern for growers of irrigated wheat.

“If you grow irrigated wheat on irrigated wheat, or a lot of irrigated wheat in a rotation, it is entirely possible that midge can build up,” said Meers.

The midge overwinters in the soil until spring moisture causes the breakup of the cocoon, and the insect pupates. “Spring moisture is critical,” said Meers. “If it’s dry, it will stay in the cocoon and try to make it through to the next cycle or the next year.”

The insects emerge as adults in late June or early July and then lay eggs on developing wheat heads. The developing larvae feed on the developing kernels of wheat, which damages the plant.

Cereal leaf beetles

Another insect that could cause a lot of potential problems is the cereal leaf beetle. The insect was discovered in Alberta in 2005 and caused limited damage in 2006.

“Every Canadian province that grows cereals has the insect,” Meers said. “We’re not concerned that much about the adult stage, what we’re worried about is the larval stage.”

Other insect concerns

It has been several years since a large outbreak of bertha armyworm across the province, but there was a significant number trapped last year.

“We’re at the low end of the cycle right now and I don’t expect that we will have trouble with the armyworm in 2010,” Meers said.

However, he added that regular surveying is always important.

“One thing I’ve learned throughout the years is that if you say something is absolute with insects then they break the rules.”

Meers said there are still pockets of diamondback moths across the province, but numbers are still down from the past eight to 10 years.

The wheat stem sawfly has a weather-driven cycle and is abundant in dry years. “We tend to get an increase in sawflies during the early harvests,” said Meers. During later harvest years, creatures which prey on the sawfly are better able to maintain control and reduce the population. “We really are seeing a big decrease in sawfly,” said Meers.

About the author

Reporter

Alexis Kienlen

Alexis Kienlen lives in Edmonton and has been writing for Alberta Farmer since 2008. Originally from Saskatoon, Alexis is also the author of two collections of poetry, a biography, and a novel called "Mad Cow."

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