Issue link: http://read.dmtmag.com/i/283151
it's easy to spot nonworking pressure gauges because the needle either bounces or doesn't return to zero when at rest. "But gauges have a tendency to slow down and not be as accurate even though they appear to be working." Pressure that's too high results in too much air vol- ume and can lead to pesticide runoff. Volumes too low can result in poor coverage. She recommends that pres- sure gauges be tested annually (a testing kit is available for $100) or replaced before each spray season. Nozzles come in many shapes, resulting in various droplet sizes and spray patterns. Though some noz- zles are more resistant to plugging, all can get clogged at some point. A regular maintenance program to clean sprayer nozzles and filters is key in making sure sprays go where they're wanted. Replacing nozzle tips can make a big economic differ- ence. Generally, 20 percent of the nozzles on a sprayer are worn and need replacement, Hoheisel reported. "If you buy 16 new ceramic nozzle tips for your sprayer at $5 each, that's a cost of $80 total. Those nozzles will pay for themselves in about five acres if you were off by 20 percent." Improve spray quality Sprayer speed is the last component that affects coverage. The optimum ground speed when driving a sprayer is 2.5 to 3.5 miles per hour. "Realistically, many orchard spray applications are done at 5 mph," Hoheisel said. "I understand growers have a lot of acreage to cover, but studies have shown that you don't save that much time increasing speeds from 3.5 to 5 mph. But you greatly affect the coverage and efficacy of your spray." Affordable devices are available to track accurate ground speed (which is not the same as tractor speed) and with GPS, where the tractor has been. "Then you know how fast the operator was going and exactly what rows were covered," she said, noting that commercially sold rate control systems also calibrate the amount of spray that's been programmed for the sprayer. Don't overlook water pH used in mixing pesticides, she noted. Water with a pH of 8 or higher can greatly reduce the efficacy of a pesticide, shortening its half-life. Conversely, a pH of 6 can lengthen the half-life and cause pesticide residue issues. The half-life is how long it takes for half of the pesticide to degrade. An inexpensive pH meter, available for around $50, can measure water pH and provide accuracy within 0.2 pH points. Hoheisel urges growers to calibrate their sprayers at least annually. A host of YouTube videos give calibration demonstrations. Flow rate meters can also be used to test nozzle output. "We monitor so much of our pest control programs, but we don't monitor enough of what we're doing with our sprayers," she said. "With inexpensive tools now available to help us test, calibrate, track, and monitor our sprayers, we can make big changes. Simple, low-cost adjustments and changes, like replacing nozzle tips, can bring immediate improvements." • www.goodfruit.com GOOD FRUIT GROWER APRIL 1, 2014 25 Water pH influence on half-life of pesticides Active ingredient pH 6 pH 7* pH 8 pH 9 Captan 8 hours 10 minutes 2 minutes Carbaryl 100-150 24-30 2-3 days 1-3 days days days Chlorpyrifos 35 days 22 days Malathion 8 days 3 days 19 hours *pH 7 is neutral SOURCE: University of Florida Orchard Equipment