A few years back Owen Olfert and other entomologists approached a group of growers with what might have seemed like an outrageous request — don’t spray for wheat midge.
They were in the process of introducing a new parasite to knock back midge populations, but there was a problem — the critter in question was susceptible to the same insecticides the growers were using to protect their crops, the AAFC research scientist told Country Guide recently from his office in Saskatoon.
The scientists knew they might be asking farmers to make a difficult decision, but they were willing to help.
“We talked to the farmers in the area and explained what we were doing, and asked them if they’d like to collaborate,” Olfert says. “We got unbelievable support, even though this meant they’d have to look after wheat midge without spraying until the new predator was established in the area.”
The growers were good to their word and several seasons later, the new beneficial insect is well established and busily eating its way through midge populations season after season. It appears to have tipped the scales in favour of growers, as it teams up with another parasite that moved in at the same time as wheat midge, keeping populations below economic thresholds.
Olfert says it’s a heartening experience that proved growers understand the challenges and benefits of an IPM approach to insect control.
One reason IPM insect control may have taken a few years to catch on is a common misconception that’s long dogged the system — that it somehow seeks to totally eliminate the use of insecticides. Olfert says that’s simply not the case. He describes IPM as an approach that incorporates a number of tools so it can leverage knowledge and understanding of both crop pests and beneficial insects.
“It’s using a combination of tools ranging from cultural controls like planting early or varying seeding rates to taking steps to protect and enhance beneficial insects, all to keep the pest population below the level where chemical control methods are necessary,” he says.
So the IPM approach can involve the use of chemical controls as part of the arsenal, but it seeks to deploy these very powerful weapons strategically in order to control the target insect without wiping out the beneficials.
“Wheat midge is again probably the best example — we’ve narrowed it down now so the recommendation is to only spray adult wheat midge after the plants are in boot, but before flowering,” Olfert says. “It is a very narrow window to control adult wheat midge, but I do see producers more and more aiming for this target.”
Taking this approach will protect wheat yield and quality, but also gives beneficial insects a fighting chance to survive. Without them, wheat midge will have a vacuum to fill and a population boom becomes more likely.
Manitoba provincial entomologist John Gavloski agrees that growers appear to be interested in this approach, noting that it can also reduce control costs over time. That’s becoming more important to farm managers as crop prices have fallen, causing every input on the farm to get a hard second look.
Lower prices make every farmer sharpen the pencil just a bit more and cast a skeptical eye on each decision, all with an eye to making the operation that much more resilient.
“When economics get tougher, everyone begins looking for ways to use inputs more efficiently,” Gavloski told Country Guide during a recent conversation.
Gavloski says the concept most growers will be familiar with is economic threshold. The simple definition is the level at which insect damage is high enough to make a pesticide application economical. But it’s not always simple to apply in practice.
For some insects, the threshold can move, depending on crop prices. With higher prices come lower thresholds, and vice versa. For other economic thresholds, such as for soybean aphid, the threshold does not change with price because it’s already well below the level where control costs equal the injury the insect would do to the crop (referred to as the economic injury level). Some recent thresholds incorporate the realization that beneficial insects can play a major role and need to be accounted for in making control decisions.
“Those beneficial insects, if they’re protected, can prevent the need for a control application either that season, or later down the road,” Gavloski explains.
That’s because, unsurprisingly, the insect population of any field is a complex web of predator and prey and for every pest there are multiple predators and parasitoids, insects that don’t eat their prey instantly but suppress them in other ways. Small parasitoid wasps, for example, lay their eggs inside insects you want to control, killing them for free. Likewise lady beetles, lacewings, hover fly larvae, and minute pirate bugs will happily devour soybean aphids.
“That means when we’re looking at aphid populations, you will make better and more economical decisions if you can identify lady beetles and these other beneficial insects, and take them into account,” Gavloski says.
That might raise the threshold high enough that a control application can be skipped entirely. Or it may mean you want to make a treatment, but pick one that’s more selective, and will protect the beneficial insects.
“Selective pesticides are sometimes a bit more expensive, but they’re often not dramatically more expensive, and maintaining those beneficial populations can lower overall costs over time,” Gavloski says. “Pesticides can be part of an integrated pest management system, but only if you’re using selective pesticides when practical.”
Scott Hartley, an entomologist with the Saskatchewan Ministry of Agriculture, echoes Gavloski’s assessment of the changing economic times.
“Higher crop prices do affect how IPM is viewed,” Hartley says. “When prices were higher, growers were still doing things like seeding early, but if they saw pests in their field, there were a bit less likely to pay attention to economic thresholds.”
However, he says, over time, the trend line appears to be in the direction of taking a multi-pronged approach, partly for sustainability reasons, but mainly for economic ones. He says growers appear to be starting to take the IPM message to heart, and more and more understand if they apply the theories, the practical result will be lower costs.
“It’s all about keeping the pest levels below the economic threshold, eliminating the need for pesticide applications,” Hartley says.
He also notes that most concerns surrounding pesticide use were based on the relative toxicity of the products and their effect on non-target organisms, rather than worries over resistance due to selection pressure through repeated applications.
“It’s true that, over time, any of these products can cause pests to develop resistance, but it’s not as big a concern as with a herbicide or fungicide,” he says. “Those type of products are applied much more frequently, while pesticides are used more occasionally.”
Scout it out
All three entomologists call scouting the most important aspect of IPM. Olfert says it’s always his first recommendation to interested growers.
“Scouting is the biggest thing,” he says. “You can’t do it and make the decisions you need to make without being out in the field, looking for pests and their biocontrols.”
Since identification is key, Olfert recommended the new AAFC publication Field Crop and Forage Pests and Their Natural Enemies in Western Canada.
“It’s available in hard copy, but you can also download it as a PDF and take your iPad or tablet to the field and use it to help identify insects and their beneficials,” Olfert says.
The guide includes photos of pests and beneficials at various stages, among other resources.
Managing and sourcing this sort of information is going to be more important as farm size continues to grow, Olfert says.
“I go out to farms today and my jaw drops at the number and kind of decisions these folks need to make.”
This reality has made hired crop scouting far more common, especially on larger farms. Olfert says he’s spent a lot of time talking to professional agronomists in the past few years. He’s convinced most are well aware of the IPM approach to insect control, but that it’s always worth bringing up.
“It might not be a bad idea to talk to them, just to make sure they’re using these strategies,” Olfert says.
There’s little question that large farms capture economies of scale, spreading overhead costs over a larger acreage. But when it comes to fine-tuning their field management to reduce costs, Gavloski says these farms have a special challenge.
“These farms get to a stage where scouting fields becomes more difficult, which can result in unnecessary pesticide applications,” he says.
It’s not a question of right or wrong, just the reality of the time-consuming process of scouting for insect pests. Proper scouting usually requires five or more randomly selected sample sites throughout the field, and the time to perform proper counts on sometimes moving or hidden pests.
That doesn’t stop Gavloski from recommending good scouting to large operations. He says it’s the bedrock of a good insect management plan that will let growers manage their pest problems, improve the economics of their operation, and make it more biologically resilient and less prone to future outbreaks.
“Scouting really is the key to it all,” Gavloski said.
Scouting provides a clear picture of whether what you’re dealing with is just a handful of pests that won’t really set back production, a hot spot that could benefit from a spot treatment, or a full-blown infestation that requires a full field treatment.
“This is why we say a minimum of five sites, spread out through the field,” Gavloski says. “For most insects a quick look along the field edge won’t give you a true picture of what’s going on. If you do that when you’re making your decisions, a lot of times you’re going to make the wrong call.”
Gavloski, says, too that while insecticides are powerful tools, they’re tools to be respected, not least because many are toxic to mammals including humans.
“Any pesticide application has its risks and benefits,” he says. “Applying an insecticide just in case an insect is present at economic levels, or as a tank mix because you are already applying another pesticide, can sometimes not only be uneconomical but costly if it also reduces beneficial insects or interrupts pollination.”