It may take a concentration less than 1/250th for Group 2 herbicides to start damaging canola, according to sprayer specialist Tom Wolf.
“That’s quite a dilute mixture,” he said. “You’d never think it would do anything.”
Wolf was one of many presenters at Canolapalooza 2017, held in Portage la Prairie June 22.
Group 2 herbicides came up more than once during the day, as farmers wrestled between proper tank cleaning and inconvenience.
“Group 2s, for a pile of reasons, are probably the worst ones (for canola damage,)” Ian Epp, agronomy specialist with the Canola Council of Canada, said. “They’re a really low-dose chemistry that takes very little actual chemical to be tied up in your sprayer to have a problem, to actually hurt a whole pile of acres. And, Group 2s, given the chemistry, they’re more likely to be tied up in a sprayer.”
Sprayers 101, an online resource co-founded by Wolf, says ammonia may be required for thorough cleanout as Group 2 herbicides dissolve better in a basic solution.
The herbicide class is commonly used in other crops and contains enzyme-blocking chemicals that hinder a plant’s ability to create protein, causing it to starve.
In canola, symptoms can appear as undersized leaves, thick leaves or purpling at the cotyledon stage, according to the Canola Council of Canada. In older plants, maturity is delayed, leaves discolour or curl into “cups,” and yields may drop, while mature plants may develop immature offshoots, stunted meristems and aborted flower heads.
Early symptoms may mimic cold stress or nutrient deficiency, a 2012 herbicide injury resource published by the council said, although herbicide damage may be more intermittent.
While Group 2 herbicides are most commonly harmful to canola, some Group 4, 5 and 14 products have also been known to cause damage.
Wolf, who also co-founded Saskatchewan-based consulting firm Agrimetrix, says tank cleaning is critical to minimize risk, despite the extra time it costs producers.
“There are two aspects to cleaning,” he said. “The first is to properly dilute what you call the remaining volume in the tank. The remaining volume is that liquid that stays in the tank even after you’ve pumped it empty or drained it, and there’s a few pieces of plumbing that you can’t drain: for example, the suction line from the tank to the pump and the return line from the pump back to the tank, which is used for pressure management or agitation.”
Remaining volume may be as much as five to 10 gallons, according to Wolf.
“Empty your tank as completely as you possibly can. We recommend that you do it by spraying your chemical out in the field — the remaining chemical. We do not recommend draining your tank anywhere,” he said, warning that a single dump of product will hinder that site’s ability to grow vegetation.
Once the tank is as empty as possible, the remaining chemical must be diluted.
Producers may fill tanks completely with water before draining, a method Wolf says is effective, but time consuming and farmers also must contend with draining large volumes of diluted chemical.
Smaller batches may dilute more effectively, although Wolf noted that cleaning might take longer as multiple batches must be sprayed out.
“The third way is a new way, and that is actually to add a second pump to your sprayer that actually then makes it into a continuous rinse,” Wolf said. “The second pump is dedicated to the clean water tank.”
Wolf argues that the third option may save time as a producer flips over to the second pump without leaving the cab and sprays out excess chemical immediately.
Agrimetrix is advocating the third option, but has had limited producer uptake on the suggestion, Wolf said.
“Once you’ve got the spray mixture diluted, you do have to clean and decontaminate all the plumbing that comes after the tank, because that is where many of our problems reside,” he added. “We have significant surface area in our black rubber hose that goes from the sprayer pump to the booms in the various sections. That hose can hold on to chemicals and you have to flush it out of there.”
Screens and the dead-end space at boom ends should also be cleaned, he said.
The lesson was hammered home by Group 2 demonstration plots, which showed increasingly sick-looking plants that had been purposely exposed to Group 2 herbicide.
Epp also pointed to Group 2 stacking within the soil, although the issue is more commonly seen in Saskatchewan.
According to the Canola Council of Canada, carry-over injury may vary widely within a field and is often more prevalent in areas with poor soil, low organic matter, acidic or basic soils or in low-moisture environments, one reason why the issue is not as prevalent in the wetter soils of Manitoba, Canolapalooza instructors said.
The council recommends that producers keep track of herbicide use and consider suggested recropping options assigned for each product.
Spray drift may also put a crop in contact with harmful herbicides.