Dicamba caution issued following U.S. drift problems

RIDGETOWN, Ont. — Canadian soybean growers are being asked to spray carefully this spring in light of the dicamba drift disaster that occurred in the United States last year.

While the U.S. incidents were linked to the illegal application of older formulations of the herbicide more prone to drift, there’s still room for caution, according to Peter Sikkema, a weed scientist at Ontario’s University of Guelph.

“Extra care has to be taken to make sure there is no injury in adjacent fields due to off-site movement of the herbicide,” he said.

Sikkema’s comment came after a presentation made by another weed scientist at the Southwest Agricultural Conference on Jan. 5. Kevin Bradley of the University of Missouri spent much of last summer investigating drift incidents in his state.

“It’s a billion-dollar issue,” he said. “I am not against the technology. I think it’s a different question as to whether we can steward this technology.”

There were 130 official reports of crop damage affecting thousands of acres in Missouri and additional incidents reported in neighbouring Arkansas and Tennessee, Bradley said.

Dicamba-tolerant cotton seed — and some soybean seed with the same trait — had been approved but not the low-drift, herbicide formulations they were to have been matched with.

Dicamba was developed in the early 1940s and continues to be used widely today. The development of dicamba-tolerant crops began in response to growing weed resistance to another commonly used herbicide, glyphosate.

Bradley said the farmers who decided to illegally spray older dicamba formulations on their dicamba-tolerant crops didn’t appreciate the high degree of sensitivity other crops have to the herbicide. In most situations, dicamba was applied to dicamba-tolerant cotton and subsequently moved into dicamba-susceptible soybeans, he said.

“There was no malicious intent. If they could roll it back to do over, I think they’d do it differently.”

More than 40,000 acres of soybeans were reported to have been damaged, along with about 1,000 acres of cotton, 900 acres of peach trees, 400 acres of purple hull peas, 200 acres of peanuts, several smaller acreage crops and a range of plants, including mature trees, located on residential properties.

The largest concentration of cases was in the southeastern corner of Missouri, which is known for its diversity of agricultural crops. A smaller concentration was in the central part of the state.

Bradley suspects the number of drift incidents was actually much higher, but many were not reported or properly identified.

The newest dicamba formulation — Monsanto’s XtendiMax with VaporGrip — was approved by the U.S. Environmental Protection Agency last fall. I

t’s intended for use with Roundup Ready 2 Xtend soybeans, the industry’s first stacked soybean trait with both dicamba and glyphosate herbicide tolerance.

Another low-drift formulation, Engenia, was developed earlier by BASF and Sikkema understands DuPont is developing another low-drift dicamba formulation.

Bradley said he noticed two types of dicamba damage during this 2016 investigation.

About 60 percent of fields had damage in a pattern consistent with herbicide drift with some parts of the field being damaged and others not.

The other 40 percent of damaged fields, where damage was consistent throughout, may have been subject to a phenomenon known as a temperature inversion. That’s when the air temperature near the earth is warmer than the air above it, a situation under which herbicide sprays can remain suspended for extended periods.

Typically, the phenomenon develops overnight and may continue the following morning. Even with slight air movement, the suspended herbicides can move for long distances, just over the soil surface.

The amount of dicamba needed to damage plants is small, with 1/20,000 of the recommended rate enough to result in visual damage. Injury that occurs early in soybeans’ growth stage is unlikely to have a negative yield impact.

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