See a bug, spray a bug might be the philosophy for some growers. But not all bugs are created equal.
OMAFRA’s field crop entomologist Tracey Baute explained that an insect-prone year like 2020, the temptation can be to spray, just in case. But with few new chemistries coming down the pipe in the next decade and increasing concern about resistance, limiting how often farmer spray for pests will be critical to maintaining functional control for as long as possible.
That’s where what Baute calls natural enemies come in. Simply, they’re other insects and pests that eat, infect or parasitize pests. Predators are the most obvious and recent data in Ontario on soybeans sheds some remarkable light on how effective they can be. According to research from the University of Guelph, an individual ladybug can eat 100 aphids per day. “On average. Some species are much higher,” Baute said. It led to the creation of what’s called a dynamic action threshold, where the decision to spray or not isn’t just based on pest population but natural enemy populations as well.
And while a scorched-earth policy of spray them all might sound like the safe measure, there’s a couple reasons it’s not. The first is resistance. Resistance is already developing in some pests to major chemistries used to control them, said Baute, and it’s not as though a whole new wave of pesticides is coming down the pipes. “We need to maintain the ones we do have as much as possible.”
The other factor is cost. Spraying costs money. Natural enemies don’t. Control thresholds were developed so producers don’t spend more spraying than they would in lost crop, and natural enemies fit into that equation as well.
Baute added that she’d never recommend natural enemies as the sole control method for pests. Unsurprisingly, predators rarely eat every single prey item in their area. But natural predators can reduce how often producers need to spray, which can both save money and make sure that resistance to pesticides doesn’t develop before farmers have a backup option. Because without a backup, natural enemies are going to the only method of control.
Obviously there’s a huge variety of natural enemy species, which can vary by crop. OMAFRA’s latest agronomy guide, available on the organization’s website, is a good resource, Baute said.