Army worms advance

Wednesday, June 6, 2012

by SUSAN MANN

If you have the greenest, most advanced winter wheat fields in your area watch out for armyworms.

That’s because armyworm moths can “actually sense how green the field is and they will lay their eggs in the greenest or the best fields,” Ontario agriculture ministry cereals specialist Peter Johnson says.

This year there is significant armyworm pressure in some fields but it’s not everywhere, Johnson says. One particularly hard hit area is the north shore of Lake Erie as armyworm moths fly into Canada on the trade winds from the United States.

But “we’ve had reports of heavy armyworm pressure from Niagara Falls to Windsor to as far north as Exeter,” he notes.

Johnson recommends farmers get out into their field and scout at dusk so they can act before the larvae get too big to control. The threshold is five larvae per square foot under one inch in length.

One unusual feature about this year is “there is quite an extended range of armyworm out there” whereas normally there is just one flush of the pests, he says. On the more advanced fields, the armyworms are already quite large and beyond control.

Once the armyworm larvae are more than one inch long the damage is effectively done. They don’t feed much more after they get to that size. When they’re about an inch and a half long they pupate, become moths and fly off to Quebec.

For some of the less advanced fields, the armyworms are extremely small, just one-quarter of an inch long, but are at quite high numbers. They need to be sprayed. “Don’t let them feed on the leaves forever,” he advises.

Johnson says this year’s armyworm infestation isn’t as bad as the one five years ago when growers didn’t catch it early enough in many fields. Farmers spayed anyway “because their wheat had no leaves left on it.” But once they’re an inch and a quarter long, it’s too late to spray them.

In addition to wheat, Johnson says they’re seeing armyworm damage in forages and a little bit in corn. For wheat, armyworms feed on the plants’ leaves. They can also start feeding on the bottom of the heads and chewing through the stems. That causes the heads to fall off. BF