Soybean farmers aren't the only ones with aphids on their minds. Canola farmers should be keeping an eye out for the common pests.

It's more difficult for aphids to cause economic damage to canola, or rapeseed, plants. But the number of different types of aphids that can infect a field are greater than with soybeans. That means the threat those aphids pose lasts longer throughout the year than that posed by soybean aphids, according to North Dakota State University Extension entomologist Janed Knodel.

The biggest concern for aphid damage at economic levels lies in later-planted fields. Bugs like the green peach aphid, cabbage aphid and turnip aphid are all more likely to cause damage at or near treatment thresholds. But, that's a moving target, Knodel says.

"There are no established thresholds for aphids on canola. In most cases, spraying is not economical, because aphids are located on the top 2-3 inch of the plant where pods are the smallest and contribute little to the overall yield," she says. "However, treatment may be justified when at least 20% of the stems are infested with a cluster of aphids in late flowering or early pod stages."

If you suspect you've got aphids working their way toward the treatment threshold in your fields, make sure you scout well. That's not just frequency, either.

"Note the presence of natural enemies as well as aphids," Knodel says. "A treatment may be necessary when the following conditions are met: 1) canola was planted late; 2) plants are still in pod development; and 3) low populations of natural enemies are present, such as lady beetles, syrphid flies, or lacewings."

• Get more information on treating aphids in canola