Too early for aphids in Ontario's soybean crop

Monday, June 4, 2012

by SUSAN MANN

The aphids southwestern Ontario farmers were seeing in their wheat crop a few weeks ago won’t affect soybeans, says a provincial agriculture ministry soybean specialist.

That’s because the aphids that attack wheat are a different species from the ones that go for soybeans. “They really have no connection,” says Horst Bohner.

Bohner hasn’t seen any soybean aphids in fields yet nor has he heard if anyone has seen any. The pests are blown in from the United States causing a lot of the soybean aphid problems in Ontario.

Aphids can reproduce quite quickly when the weather is dry and hot but in a cool, wet year aphids don’t proliferate as well. Soybean aphids seem to like temperatures in the 25 degrees Celsius range. If it gets hotter than 30 degrees Celsius their reproduction slows down and their numbers might not explode.

In wheat, agriculture ministry cereals specialist Peter Johnson says more than three weeks ago there were some high aphid numbers in wheat fields predominately in Kent County “and we were doing a little bit of spraying.”

There were only a few isolated fields that got enough aphids to be over threshold.

Johnson says it’s quite unusual in Ontario for there to be aphid numbers in wheat that are significant enough to raise concerns. The standard threshold is 12 to 15 aphids per stem before heading and 50 per stem once the head has come out.

There are always some aphids in wheat every year, he adds. But it’s unusual to see high enough numbers that require spraying, he explains, noting the species they found predominately this year was the bird cherry oat aphid.

One of the main things aphids do in wheat is transmit a disease called barley yellow dwarf virus that affects all cereal crops, including barley, oats, spelt and rye along with wheat.

For soybeans, typically there are a few aphids in a few pockets across the province every year. But the real question is whether they will reproduce quickly and move around. For that to happen, it depends on the weather and the number of beneficial predators around. Bohner says it’s way too early to predict what kind of aphid situation there will be in soybeans this year.  “All I know for sure is I don’t see any right now.”

So far the soybean crop has had a very good start. “Whenever you have heat early on like we did after seeding, beans love that so they had a good push to get out of ground,” he says. BF