Herbicide drift often occurs when it is least expected – during a still, calm morning, according to Eric Webster, LSU AgCenter weed specialist.

Webster said just because it seems like no wind is present at ground level doesn’t mean that condition exists a few feet above ground.

"The worst times are when the wind is zero to 2 miles an hour," Webster said. "That’s when you get those inversion layers built up."

A field surrounded by tall vegetation increases the variation of wind direction, he said.

Using a ground sprayer is a good way to avoid drift problems, he said, although it still is not a guarantee.

Farmers can contaminate their own fields with unintended applications of herbicides if tanks are not properly cleaned, Webster said. "It’s always a good idea to triple rinse after spraying."

Using research plots, Webster and his staff are studying the effects of drift from the herbicides Roundup and Newpath at different concentrations.

Webster is developing a Web site to show symptoms of drift from different herbicides and a pamphlet to help diagnose problems. He said both resources will be ready for the 2009 growing season.

Webster said examining a field for suspected herbicide drift requires a broad view of the affected area. "The best thing you can do is stand back and take a look at the situation."

He said many of the signs of herbicide damage mimic symptoms of nutrient deficiencies because a plant hit with herbicide stops growing.

Browned leaves on nearby trees can offer clues as to the direction the drift traveled, he said.

Herbicide drift can travel as far away as a mile on a still morning, Webster said. Last year, he said, drift from an airplane became evident on rice 150 yards away, but the highest concentration was a mile away.

Newpath drift often results in rice heads failing to emerge from the plant sheath, rotting inside the plant, he said, while the heads in a rice plant contaminated with Roundup often emerge but are sterile.

Roundup is evident on rice with twisted leaves, short internodes and heads shriveled and malformed, he said. In some instances the head locks up in the leaf sheath.

Newpath on young rice will result in green and yellow striations on the leaves, and growth of the main stem stops.

Liberty Link soybeans, which can withstand the herbicide Ignite, will be grown commercially for the first time this year. Webster said Ignite is a contact herbicide that doesn’t move through a plant system, so he does not expect it will cause as many problems as glyphosate, which is the ingredient in Roundup. Some crops, such as rice, can survive Ignite, although yield might be decreased by 10-15 percent.

Webster said rice damaged at the two- to three-leaf stage can overcome herbicide injury. "The worst thing is to flood a field," he said.

Allowing a field to approach drought conditions can promote root growth that will enable plants to recover, he said.

When Webster is called to a suspected drift case, he is more interested in the what-did-it than the whodunit. He examines a field to find out what chemical, if any, has caused a problem, but he is not involved in investigations.

"I’m not there to point fingers or accuse anyone of doing wrong," he said. "I’m there to give the producer some options."

Complaints aimed at enforcement should be directed to the Louisiana Department of Agriculture and Forestry.

Bruce Schultz

(This article appeared in the winter 2009 issue of Louisiana Agriculture.)