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Corn+Soybean Digest

Perennial Weeds Can Quash No-Till

If you've been no-tilling several years and don't have a special strategy to battle perennial weeds, you're in for some misery.

That's almost a sure bet. But if you do it right, you can whip any perennial invasion nature throws at you.

That's the assurance of George Kapusta, a Southern Illinois University weed scientist. In more than 25 years of no-tilling, he's never found a perennial critter he couldn't control.

The challenges are probably stiffer in no-till soybeans in the South than in the North. But, in both cases, weed scientists and growers recently got a new and potent weapon - the Roundup Ready system.

"It's a fact of life that, if farmers are in no-till for an extended time, they are going to get more and more perennial weeds unless they get on them like mad wolverines when the first ones show up," says Kapusta. "So they have to plan a strategy to avoid what can become real problems."

"In the western part of our state, we have been in continuous no-till corn and soybeans long enough that the perennial weed problem is increasing quickly," warns Alan York, North Carolina State University extension weed scientist.

"I don't think we are losing tremendous amounts of yield, but some of those fields look ugly. And the number like that is increasing.

"It's time for a wakeup call on this problem," York adds. "We now have some options that are pretty darn good, but too many growers just aren't doing it." Kapusta agrees.

"Occasionally, farmers will get into such a predicament that they absolutely don't know what to do," the veteran scientist observes. "Their fields might be 50% infested with perennial weeds."

It's no big sweat to control perennial grasses, the scientists say. There are several herbicides that nail them readily, if you match the chemical to the problem species.

But broadleaf perennials are altogether another matter.

They vary somewhat by region. But the major culprits include common milkweed, hemp dogbane, Canada thistle, trumpet creeper, honeyvine or climbing milkweed, pokeweed and rubus species (like blackberries and dewberries). Add to that list tree saplings in wooded areas, "which can be rough on machinery," reminds York.

Poor control of perennials without tillage is a matter of herbicide application timing.

"With perennial weeds, there is no question that there is a mismatch when trying to control them with one application compared to annual weeds," Kapusta warns.

"With annual weeds, we need to apply the herbicides quite early. At that time, we will burn off what perennial weeds are emerged - grasses or broadleaves. The problem is, they will come back. And it doesn't matter what herbicide you use. Even with the most effective herbicides on perennials, a second application is a must, and it might take higher rates, too."

Here's where the battle plan begins with sharp growers who have no real perennial weed problems after years of no-till, Kapusta says.

Perennials may be transported from infected fields by custom applicators or by the grower himself. Rhizomes or seed may be dragged in on tires, etc., from fields five or 20 miles away. If you watch closely, you'll see maybe just three or four perennial weeds at the field entrance the first year.

A sharp manager will watch for them and attack them like a mad grizzly with a pistol-grip sprayer or a hand sprayer.

You can use 2,4-D, Banvel, Roundup or whatever. Even if you kill a little corn or soybeans in the process, it'll be well-worth it in the long run.

If you don't act, there'll likely be three or four nearby spots the second year. By year three, there will be several spots scattered around the field. And by the fourth, fifth or sixth year, it starts getting even a poor observer's attention.

If you've rented new land where perennials are scattered throughout the field but aren't thick yet, hit them with a wick applicator and Roundup, or the best other herbicide choice for that species, Kapusta advises.

"It's an inexpensive way to go, and it can give a lot of control of a lot of perennial species."

If you buy a new piece of land that's already badly infested, or you've let perennial weeds get the best of you on your own land, you may have to take drastic measures.

If you're on erosive ground and far enough south to doublecrop, you may want to take the first crop off, then forgo the doublecrop soybeans. Spend the rest of the summer hammering those perennials with multiple applications and high rates of Roundup or another chemical effective on your problem species, Kapusta suggests.

If you're in the middle or northern Corn Belt where doublecropping isn't an option, it has been a tougher challenge. But with the Roundup Ready soybean system and now Roundup Ready corn, you have potent new weapons. Even so, it may take multiple applications and cranked-up rates, Kapusta cautions.

Don't procrastinate on perennial weeds. Have at it, these scientists challenge.

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