August 17, 2004

Research station manager offers primer on weed control

by K.C. Jaehnig

After more than 20 years at Southern Illinois University Carbondale's Belleville agricultural research station, manager Ronald F. Krausz knows a thing or two about controlling weeds in corn.

His No. 1 tip: Read the label on the weed killer package.

"It's the most important thing we don't do," Krausz told farmers July 15 at SIUC's annual field day in Belleville.

Labels tell you how much weed killer to apply and when and what kinds of adjustments to make for your particular soil type.

"They're pretty boring, and it seems to me they could be fine-tuned a little -- every time I go to the label, I don't find what I need until I've read the whole thing," said Krausz, who admitted skipping this step himself every now and then.

"And with the Internet, reading the label has become a lot easier to do. If you go to, you can access the labels for all the compounds available. It makes good reading before going to bed -- it will put you right to sleep.""But if I read the labels, I wouldn't get surprised," he added.

No. 2 on the Krausz tip list: Know your weed spectrum.

"Next to reading the label, it's probably the most important thing you can do," he said.

"If you know your weed spectrum, you can fine-tune your weed control, and sometimes you can get by with less herbicide."

Krausz suggests taking a notebook along when you're combining and writing down every weed species you see as well as its location in your field.

"It's the best time to assess how well your weed control is working because you go across every acre," he said.

But in general, avoid the temptation to skimp when applying herbicide, Krausz advised.

"A lot of you will say, ŒI can use lower rates and get good weed control,'" he said. "If you can, you're the exception to the rule."

Farmers who do manage to keep weeds down with lower application rates know their fields and the weeds in them. And just because your neighbor gets away with using less weed killer doesn't mean you can, too. The conditions in his field may differ from those in yours.

"To be on the safe side, using a full rate is the better way to go," he said.

Krausz also recommends upping the amount of atrazine applied to fields.

"Here in Southern Illinois we need two pounds of active atrazine; most pre-mixes have between 1.3 and 1.6 pounds," he said. "You can add atrazine to your pre-mix or use it as a post application later on."

Lexar, a new three-way pre-mix with more atrazine, will be available next year.

"It's almost like it was made specially for Southern Illinois," Krausz said. Lumax, another three-way, contains the same ingredients but in different ratios. "It has a lower rate of atrazine, so it's geared more to the northern part of the growing region," Krausz said.

"We have a different weed spectrum in Southern Illinois, so we need a higher rate. And we don't have the same carryover concern, so we can use higher rates without worrying about injuring next year's soybeans."

Farmers were quick to note that this would be expensive. Yes, Krausz acknowledged, this strategy would cost more up front, but rampant weeds cut yields, which also takes money from farmers' pockets. And the longer they put off controlling weeds, the worse the problem becomes. It can take two years of fighting grass species to get back to where the fields were before the weeds took over. It can take five years to recover from broadleaf invasions.

"If you have a species that is out of control, it's better to pay a little more money now than pay a lot of money later on," Krausz said.

"Say you have a million weeds per acre. If you control 90 percent of that, you still have a mess. Get it under control while there's not a heavy infestation."

When applying weed killer, use a two-pass system.

"I've gone to that on this farm because it gives the most effective, consistent weed control," Krausz said.

"But it's a planned two-pass. I don't put it out there and then wait until every last weed comes out before spraying again. When the corn or the weeds are at a certain height, I'm going to apply more herbicide. Weeds can grow 5 to 6 inches a week. Don't wait until you have 10- to 12-inch weeds. You want to be out there before the corn is at the V-5 stage because that's when the plant determines its yield."

If all attempts at control fail year after year, farmers should think about switching to a genetically modified variety such as Clearfield, Liberty-Link or Roundup Ready corn.

"When you go to a genetically modified corn, you can use a herbicide that's nonselective," Krausz said. "It will kill everything -- grasses and broadleaf weeds alike."