From the church of the California vineyard comes the request — “Let us spray”.
OK, bad puns aside, spray technology continues to improve from the early days when chemicals were applied by hand-held high-pressure spray guns — time-consuming and labor-intensive because it took three people to accomplish the task, a tractor driver and a worker on each side of the platform to spray the rows.
Reference that methodology, not many growers today will say, “I miss the good old days.”
Innovations, like the first Air-O-Fan sprayer in Gilroy in the 1940s, made the job easier for Santa Clara Valley farmers. A 30-inch centrifugal fan powered by a gasoline flathead V8 engine allowed one person to empty a 500-gallon supply tank, cutting task time and improving efficiency by using the air to carry droplets instead of relying on the accuracy of a handgun.
A lot has changed since then, as farm advisers are outlining to growers as they prepare for the spray season for Pacific spider and Willamette spider mites.
Supported by a Pest Management Alliance grant from the California Department of Pesticide Regulation, University of California Cooperative Extension Farm Advisers Lynn Wunderlich and Franz Niederholzer are making growers aware of available tools and aspects like ground speed and air volume as assessment of coverage accuracy.
“With all our rain, growers are working with full canopies this year and that means a lot of leaf area to cover,” Wunderlich told Grape Line. “Because we’re further ahead than usual, its veraison time and growers are either into or just out of powdery mildew spraying or combatting spider mites, and either way, they need good coverage on the underside of the leaves.
“There’s no one-size-fits-all when it comes to spraying and the interaction of the fan and ground speed in relation to the canopy (and whether or not there’s been any management like shoot thinning, shoot removal, or leafing),” she says. “At this time of the year, there’s a risk of traveling too fast. You need to slow down and let the fan do its job, penetrating the canopy.”
High temps, low humidity
Now that the weather has warmed up, it’s brought with it high temperatures and lower relative humidity. “That’s a combination where smaller spray droplets, thought better for coverage, can evaporate quickly from the cone jet nozzles most common for air blast sprayers,” she says. “There’s a new air induction nozzle, currently popular in Europe, that produces larger droplets that might be a better fit for this time of year.”
Wunderlich suggests using flagging in combination with fans and ground speed.
“You can put flagging on the opposite side of the row you’re traveling down and see how the flags flutter to help you determine whether or not you have enough air. It’s nothing fancy, just another practical tool that growers and applicators use.”
Niederholzer, who specializes in tree crops, stresses the importance of coverage assessment.
“Most growers don’t have a system to assess the effectiveness of their spraying aside from taking a visual of what the droplets look like on foliage,” he says. “You’ve really got to get into the canopy to make sure you’re getting uniform delivery, especially in grapes at this time of year where you want coverage of leaves, stems, and the waxy bunches as they develop and fill.
“What’s the sense of spraying unless you can determine the level of success? You can’t be confident, shouldn’t be confident, unless you get in there inside the canopy on the clusters to measure representative coverage,” he says. “If spray isn’t getting through, just think of the money you ineffectively put through the nozzles in a 100-acre vineyard during a year.”
Calling Coverage Assessment “one of the less frequently addressed steps in the process”, Niederholzer suggests consideration of water-sensitive paper (like products from Syngenta or TeeJet Spray Cards or SpotOn Spray Paper) where spray droplets turn blue on a yellow background and provide a historical row-by-row record of how effective coverage was — or the use of an organic Kaolin clay product (that dries alabaster white after spraying).
For more news on pests, disease management and other issues affecting vineyards, subscribe to the bi-monthly newsletter The Grape Line.