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Published March 12, 2012, 10:52 AM

Reaching resistance

VALLEY CITY, N.D. — In early March, there seemed to be one topic at farm meetings in the Red River Valley — weed resistance to glyphosate, or Roundup.

By: Mikkel Pates, Agweek

VALLEY CITY, N.D. — In early March, there seemed to be one topic at farm meetings in the Red River Valley — weed resistance to glyphosate, or Roundup.

“When it comes to Roundup Ready resistant weeds, we’ve got to pay attention guys,” said Darren Hefty, a partner in Hefty Seed Co. of Baltic, S.D., which also involves a television show called “Ag PhD.”

“We’re starting to see a lot of ragweed that’s resistant in North Dakota. Right across the border in South Dakota, South Dakota State University has documented Roundup-resistant kochia, and Roundup-resistant pigweeds,” he told attendees at the North Dakota Winter Show in Valley City. “You have to know some of those seeds are going to be up here.”

Hefty listed weeds in corn: marestail, waterhemp, ragweed (both common and giant), lambsquarters, wild buckwheat, velvetleaf and kochia. In corn, there are various options for pre-emergence herbicides to knock out most of them, but the post-emergence options are largely Status (5 ounce) or Laudis/Atrazine on velvetleaf. “For the most part one or two products get just about everything, so it’s nice: you don’t have to tank mix five things together,” Hefty said.

But on soybeans, it’s different. “You look at the whole list of weeds, there’s hardly a product that’s used twice,” he said. “That was really the frustration in the 1990s that led to Roundup Ready soybeans taking over the market.”

Hefty offered these recommendations for spraying Roundup:

• If it’s forecast to be below 50 degrees Fahrenheit for nighttime lows, either two days before or two days after spraying Roundup, the rate needs to be increased by 50 percent to be equally effective. “When it’s cold the plants are going to be growing very slowly, so slowly that the plant has time to break that down and make it ineffective,” he said. The other option is to wait for it to warm up.

• With Roundup currently at $2 to $3 an acre, an increase of the rate by 50 percent only costs $1.50. “It’s really not expensive to increase your rates,” he said.

• If the nighttime temperatures are forecast at 32 degrees or less within two days prior to or after spraying, then “absolutely do not spray.” “Don’t spray it, you’re wasting your money,” Hefty said. He said farmers offer anecdotes about how this works. “Yeah, occasionally it will work fine, but more times we have trouble,” he said. He said he and his brother look at Roundup problems and they are often weather-related.

“I’m not saying there aren’t resistant weeds, there certainly are,” Hefty said, but better application will make a difference.

He points to North Dakota State University and South Dakota State University research on spray tips. He noted that one of the tips — an Extended Range Flat Fan, at 40 pounds per square inch and 8 gallons per acre — showed increased coverage. “Obviously, there’s some drift issues,” he said. “If you’re out there with that flat fan, you can’t be doing it when it’s windy.” Drift control nozzles are available, yes, but they come at the expense of coverage and weed control.

Hefty also suggested spraying the weediest fields on the calmest, best spraying days. “In North Dakota, I know we get at least two or three of those each summer,” he said. Conversely, fields that have the fewest weeds can be sprayed on the “rough days.”

He said farmers could also consider using a drift retardant. He suggested hydroxypopyl guar (HPG) rather than polyacrylamid, or a TurboTeejet brand or an air induction nozzle tip to reduce drift, if necessary. He said this can also reduce coverage but can allow spraying on windier days. He suggested farmers choose a triple-nozzle body — or even a five-way nozzle body — so the applicator can switch easily from one to the next.

“You mix your batch up, you’re out there spraying and all of a sudden the wind comes up. All you have to do is walk behind your spray boom and click, click, click down the row. In five minutes you’re back in the sprayer, and you’re using those drift control nozzles,” Hefty said. “You can reduce your problems that way and get the most hours of each day, using your flat fan nozzles.”

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