The sensitivity of soybeans and other plants to dicamba — a volatile auxin-based herbicide employed in various forms since the 1960s — is extreme. Even trace amounts can cause significant damage to susceptible crops, meaning proper equipment cleaning is critical to avoiding unintended problems.
Why it matters: Use of the herbicide will increase with the introduction of dicamba-resistant crops. Thorough flushing of sprayers with an ammonia-solution followed by water can prevent damage to non-resistant crops.
Ammonia is often used and required by pesticide labelling to help neutralize dicamba in sprayer flushes. Sprayer rinsing tests performed by ag-ministry experts, however, show ammonia can make the danger posed by dicamba rinsate (contaminated wash water) more acute for a short period.
Conducting field tests
In an article published on Sprayers101.com, Jason Deveau — application technology specialist and “spray guy” with the Ontario Ministry of Agriculture, Food and Rural Affairs — details the results of a field study investigating how dicamba can be most effectively removed from sprayer systems.
The researchers employed multiple rinse cycles in both continuous and serial rinse groups. Some groups also contained label-recommended levels of ammonia in the rinse solution, while others just contained water.
They then used a bioassay (measurement of potency) to indicate the amount of dicamba present in each liquid group. In this case, any visual injury on conventional soybeans indicated the presence of dicamba residue.
Some obvious (and not-so-obvious) findings
While the damage caused by each liquid group diminished with each rinse cycle, Deveau and his colleagues found the group including a one per cent ammonia solution caused significantly more visual injury.
“We speculate that the ammonia was more effective at removing dicamba from the sprayer, or it increased the residue’s potency. This is why it’s very important to follow ammonia rinse with a water rinse.”
This assessment, he says, is in direct contrast to recent conclusions drawn from a multi-year dicamba residue study conducted by the Weed Science Society of America (WSSA) — which found no difference between the use of water or water and ammonia when cleaning.
Deveau and his colleagues also found continuous rinsing was as effective at removing dicamba as four-volume rinsing (or flushing the entire system in four separate batches), and took substantially less time to achieve the same level of cleanliness.
Andrew Geerligs and Richard Anderson say performing a final rinse regardless of the cleaning method is critical.
“Farmers who forget the ammonia, we see it on their crops,” said Anderson, BASF’s southwestern Ontario senior business representative. “A triple rinse system is standard. It helps clean the chemical out because you can’t dilute it down.
“As little as three millilitres can contaminate a 1,000-gallon tank,” says Geerligs, BASF Canada’s corn and soybean crop manager.
Buy new hoses
Aside from the contradictory findings regarding ammonia, the WSSA study also concluded that older, more worn-out hoses made of PVC/polyurethane blends and synthetic rubber harbour more dicamba residue, and thus pose a greater risk to subsequently sprayed crops. Knowing this, the American researchers say, gives farmers a heads-up that more thorough cleaning will be required; it also provides a reason to augment equipment with less susceptible polyethylene hose.
While potentially helpful, however, Deveau in an interview said there are no great revelations in such conclusions.
“It’s basically saying old, cracked hoses aren’t as good. They have more surface area and harbour residue,” he said.
At the farm level, Deveau and his ministry colleagues say farmers who have used dicamba or similar chemicals can take a number of extra steps to ensure they eliminate or at least mitigate the risk such residues pose to them and their neighbours’ crops.
- First, ensure there are no acidic solutions present in the tank before using dicamba in the first place. Doing so turns a comparatively benign dicamba solution into a much more volatile “1960s style chemical” — which isn’t good for anyone.
- Second, ensure all dead-end lines, filters, and nozzles are thoroughly washed. As represented in Deveau and his colleague’s work, dicamba residue in the remaining parts of the sprayer (not just the tank and hoses) can be just as deadly to non-target plants.
Deveau reiterates that performing regular rinses, awareness of what was previously sprayed, and not leaving product in sprayer lines for extended periods is important. He also says keeping the sprayer hydrated prevents chemical residues from drying, thus making for an easier cleaning process.
Geerligs and Anderson agree, but add cleaning regimes should also include the pumps used to transfer product, as well as the outside of the sprayer itself.
“We always forget about the outside,” Anderson said. “Where there’s an issue, it’s because something’s been overlooked.”