Farmers across the Prairies might be wise to spray for insects this year even if they find fewer bugs than what they would normally consider the economically viable point for spraying.
The economic thresholds for applying insecticides are dropping as commodity prices rise. The higher the price farmers can get for their crops, the less damage the crops can withstand before it pays to control the problem.
With grain and oilseed prices higher by an average of about 20 percent over the past two crop years, producers must adjust their control strategies, said Agriculture Canada entomologist Hector Carcamo.”You need to consider controlling lygus bugs, for example, at a far lower number (of insects) in canola when it is $9 a bushel than when it is $6,” Carcamo told the Southern Applied Research Association’s Diagnostic Field School in Lethbridge last week.
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When canola is $300 per tonne and the cost of control is $10.50 per acre, the economic threshold for the insects is 12 lygus bugs per 10 sweeps with a sweep net.
Canola at $220 per tonne has an economic threshold of 17 lygus bugs per 10 sweeps.
If insecticide costs increase, then the number of bugs increases as well. At $13 per acre, 21 lygus bugs becomes the economic threshold for treatment.
John Gavloski of Manitoba Agriculture said most published ranges for insect control from previous years are still relevant, but producers should consider the bottom end of the ranges in all crops as the current economic thresholds.
“If the range (for economically effective control) for your crop is 20 to 30 insects then consider 20 as the right number this year,” he said.”Insecticide costs may be up, but commodity prices are the more important factor.”
Consider yield potential
Gavloski also noted that the thresholds are based on average crops and producers should assess their potential yields.
“If you have a low yielding crop, then you have to think about how much you are willing to invest to control damage,” he said.
Lloyd Dosdall of Alberta Agriculture said higher grain prices should drive more producers into the fields, sweep-nets in hand.
“There is more money at risk this year and that should provide greater inspiration to find out what is out there,” he said.
Pea aphids and wheat midge have reached economic thresholds in some areas of Manitoba and Saskatchewan. Control measures for midge are complete in earlier crops and some spraying is ongoing in later cereals. Midge control begins with one per five heads of wheat.
Jim Coward of Drinkwater, Sask., said he has nearly finished spraying for orange blossom wheat midge on his farm.
“I think I’m like most producers, we hate to spray for insects. You kill the beneficial ones too. But the cost is just too great if you don’t. The crops are good and prices are up a bit and we need to protect the yield to stay viable.”
Aphids in peas have an economic threshold of one to four aphids in 20 centimetres of stem in mid to late flowering; Bertha armyworm control begins to pay off when there are 22 larvae per sq. metre, costs are $10 per acre and canola is $8 per bushel; diamondback moth control begins to pay dividends when 200 to 300 larvae are found per sq. metre.
Odd critters
Carcamo said producers should contact provincial entomologists if they encounter damage from insects they can’t identify.
“There are some new pests out there. Some haven’t caused economically significant damage yet, but we expect there will be new challenges for pulse crops and cereals over the next few seasons,” he said of cereal leaf beetle and pea leaf weevil.
Economic thresholds and control strategies are available for insect pests at www1.agric.gov.ab.ca/,www.gov.mb.ca/agriculture/news/insect/index.html and www.agr.gov.sk.ca/docs/production/thresholds.asp.
