Most farmers are more worried about drift if they’ve got herbicide in the tank, but at least one spray expert says those same concerns should apply to fungicide and insecticide.
“I can’t tell you how often I hear, ‘Oh, it’s just a fungicide, fog it in,” said Jason Deveau, the fondly nicknamed “spray guy” from Ontario’s Ministry of Agriculture, Food and Rural Affairs and developer of Sprayers 101, a blog aimed at best spray practices and innovations. “Pesticide drift is pesticide drift, whether it has instant visual damage or economic damage, or not.”
It’s a perspective that Justine Cornelsen of the Canola Council of Canada agrees with, although she says the implications for neighbouring crops are generally not as severe when applying fungicide or an insecticide.
“With insecticide drift, you’re worried about wiping out your headlands,” she said. “That’s where all the beneficial insects, your pollinators are hanging out.”
Fungicide may come with fewer overt impacts, she added, although she noted that the active ingredients in an insecticide or a fungicide might not be registered for other crops.
Wind may not be the villain farmers assume, Deveau said.
“A lot of growers are now moving towards nozzles that produce a ‘coarse’ or larger spray quality,” he said, although he noted that even a sprayer calibrated for large droplets will create some fine particles more likely to blow.
When combined with a lower boom and slower speed, the spray expert argues that farmers can comfortably spray in “moderate” wind.
There’s no set number to go with that recommendation, he said, although 10-15 kilometres an hour is “not unreasonable,” as long as the farmer’s mental calculation includes what is vulnerable downwind.
In fact, he argued, a moderately windy day is far better than early morning or evening calm when inversion risk is up and stagnant air means fine spray may not disperse.
“As you drive back and forth and back and forth, you can’t see it, but you’re leaving a fog all around the sprayer that you’ve been driving back and forth and it just hangs there. And the reason inversions are so brutal is because they’re unpredictable. Once they burn off and a light wind starts up, we don’t know where it’s going to go,” he said.
How windy is too windy?
Farmers may want to look past the Beaufort scale when measuring wind, Deveau said. Instead, he urges, “common-sense” thinking that takes into account wind direction, travel direction, and wind measured at boom height in the farmer’s field.
“Recognize that if that says 15 kilometres an hour and you’re driving 15 kilometres an hour into that wind, you now have 30 kilometres an hour,” he cautioned.
“When the grower has to make the call and they go, ‘I’ve been rained out and we’ve got to get it on and integrated pest management tells me now is the time to go, but it’s 12 kilometres an hour and I’m occasionally driving into it, what do I do?’ maybe that’s when you make the changes,” he said. “Well, I guess I’ll slow down a little. I guess I’ll drop my boom a bit. Maybe I should go to the coarser droplet and that means carrying a bit more volume. You can make those changes to your program to compensate for weather that’s on the edge.”
Tom Wolf, president of Saskatoon spray company Agrimetrix, recently took a hard look at Delta T, an Australian concept that uses temperature and relative humidity to gauge evaporation, and therefore, drift risk.
Knowledge from Down Under warns that evaporation will be too high if Delta T tops eight or 10, while spray that does make it to target will dry quicker and be less effective. Too low (below two), and small drift-friendly droplets will not evaporate, also raising drift concern, he wrote on a recent post on Sprayers 101.
The addition of Delta T has been useful in North America, Wolf said, although he cautioned against using that measure alone.
“Over the past 10 to 20 years, we’ve observed greater use of low-drift sprays, with the coarser sprays’ larger droplets resisting fast evaporation,” he said. “In the past five to 10 years, water volumes have increased due to our heavier reliance on fungicides, desiccants, and contact modes of action. Both of these developments have helped reduce the impact of a dry atmosphere. We simply can’t say if a Delta T of 10 is too high with these new application methods.”
Wolf advised farmers to watch Delta T over time with the same product, and add that experience into their decision.
For his part, Deveau repeated his advice on common sense.
“If it is hot and dry, then yeah, your spray is going to be much smaller when it gets to the target, if it gets there at all,” he said. “If you add hot, dry and windy, pack it in.”
This article originally appeared in the July 16, 2018 issue of the Manitoba Co-operator.