No easy solution for dicamba drift problem


Despite the creation of new dicamba formulations that are much less volatile and an unprecedented education campaign on how to reduce spray drift, reports of dicamba drift injury are piling up in the U.S.

The complaints coincide with the release of Monsanto’s Xtend soybeans, which contain the dicamba tolerance trait that many farmers have been excited to gain access to as it’s a new tool for managing glyphosate-resistant weeds. The company says American farmers planted 20 million acres of Xtend beans this spring. Canadian farmers have also quickly switched to new Xtend varieties. (Strong soybean seed sales were highlighted as one of the main drivers for Monsanto posting better than expected third quarter financial results this week.)

So how did we get to this, with drift injury reports on non-dicamba tolerant beans adding up to the point where the Arkansas State Plant Board has implemented an emergency ban on the use and sale of dicamba?

“I don’t think we have a situation that is all that new. Drift is a very normal byproduct of a spray application. The key difference in this situation is we have a susceptible crop that is more susceptible to dicamba than any other previous example that we’ve had in agriculture,” explains Tom Wolf of and Agrimetrix in the interview below. “A dicamba-applied plant can show cupped leaf symptoms that look alarming at 1/20,000th or 1/30,000th of the label rate.”

“I think we’re having less drift than usual. It’s just that it’s showing up because of the sensitivity of the beans,” he continues.

To understand how dicamba is moving off-target, we first have to understand there are two main types of drift:

  • Droplet or particle drift, which happens at the time of spraying. Even low-drift nozzles will create some fine droplets that can move. The massive education effort has focused on training farmers and applicators on how to minimize droplet drift by using the right nozzles and so on. “I really believe that dicamba is being applied safer than most other products because of the incredible effort, so I don’t think there’s a lot of room left to improve that within a practical bound,” says Wolf.
  • Vapour drift is much harder to manage, as some chemicals, such as dicamba, can convert from a liquid to a vapour due to temperature rising, even days after the chemical has been applied. This is referred to as volatility (glyphosate, for example, is not volatile). The vapour is then easily moved with wind or air currents, such as inversions. New dicamba formulations are much as nine times less volatile than the original formulation, says Wolf, but they can still move as vapours. Certain tankmixes can also increase the risk of vapourization, even with new formulations. Spraying on and/or before cool days will reduce risk of vapour drift, he notes. (Read more on vapour drift on Sprayers101.)

So what can be changed to prevent these drift complaints and sustainably maintain access to this technology?

If vapour drift is the problem, Wolf says dicamba formulations with even lower volatility will need to be developed, but that won’t happen overnight.

In light of the extensive precautionary awareness effort on reducing drift, he reiterates there likely isn’t much room to improve or regulate application procedures to further reduce droplet drift.

Producers in areas with high drift reports could also switch to all dicamba-tolerant soybeans, but that wouldn’t help other susceptible crops and trees, including high value horticulture production.

“It was a 20 million acre experiment. Maybe a smaller rollout would have given us a chance to react in a different way, but we’re so committed to this technology right now,” Wolf says. “It’s not an easy solution.”


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