Issue link: https://read.dmtmag.com/i/744696
42 NOVEMBER 2016 GOOD FRUIT GROWER www.goodfruit.com drift and cost, than they can with those so-called "legacy sprayers." Of course, Landers also recognized that many growers may not be in a position to buy a machine worth hun- dreds of thousands of dollars — there's a reason some people still use granddad's sprayer. For those growers, he recommended tips and tools for improving effectiveness. The dynamics of spray It's all about matching air speed and volume to the growth stage of a vineyard or orchard canopy. Too little air results in poor penetration, while too much results in spray drift and a failure to adequately deposit the spray where it's needed. The latter point seems counterintuitive, but in 1904, a little-known German physicist named Ludwig Prandtl revolutionized fl uid dynamics with his theory that high air speed applied in a liquid diverges around an object when it reaches it and then converges again behind it. The untouched area on the backside of the object and behind it is referred to as the boundary layer. The greater the air speed and the rounder an object — like, say, an apple — the larger the boundary layer. In addition, the large canopy of a traditional orchard allows for more turbulence to be created; when the air fl ow hits the tree, that turbulence in the canopy causes droplets to fall out of the spray cloud and stick to fruit and leaves. "Now, with these modern trees and narrow, very narrow, very well managed canopies — we have trees that are summer pruned, exposed apples — we no lon- ger have that air turbulence," Landers said. The spray launches onward, rather than stick to the tree. Which means growers need to start thinking differently about how they apply their chemicals, he said, particularly since sprayers only provide between 55 and 65 percent coverage anyway, resulting in "huge wastage." Understanding canopy density Landers already has patented a louver technology, a metal panel that can be retrofi tted to a traditional airblast sprayer, to adjust air fl ow. Now he and his postdoctoral researcher, Tomas Palleja, are studying ways to estimate canopy density to reduce air fl ow where it's not needed. The density of a fruit wall can vary anywhere from 30 to 75 percent, but too often, growers fail to adjust the air PLAY See the spray technology at work at goodfruit.com/media