Spider mites attack soybeans and now corn

Dry conditions across the province have encouraged an infestation of soybean and corn-sucking spider mites.

They look like little brownish-grey specks of ground pepper but can cause big losses in yield.

Spider mites are around most years but because it’s so hot and dry this year, they’re migrating fast from soybeans to corn. OMAFRA says the threshold is only four spider mites per single corn leaf before you’ve got a problem.

"They are yield robbers," said OMAFRA’s soybean specialist Horst Bohner. "They are across a huge geography, right across Ontario. I haven’t seen spider mites like this since 2003."

If you’re not looking closely, you might think the pale corn leaves are caused by drought, he said, adding that spider mites also make corn leaves look sandblasted.

One way to check for spider mites is to tap a corn leaflet over a white piece of paper and look for specks of brownish grey that fall onto the paper. But they’re hard to spot. It takes 25 of them in a row to equal one inch. While some farmers will have had to spray, a change in weather can knock down population, said OMAFRA crop specialist Gilles Quesnel. It needs to rain while temperatures drop under 25 C for two consecutive days, he said.