Issue link: https://read.dmtmag.com/i/514197
38 JUNE 2015 GOOD FRUIT GROWER www.goodfruit.com H ow do fruit growers adjust spraying to fit the sizes of trees in their orchards? "Trees have gotten smaller and canopy volume has decreased, but pesticide labels are still written in terms of so much per acre," said Dean Polk, a Rutgers University entomologist who is its tree fruit IPM coordinator in New Jersey. As products have gotten more expensive, growers have every rea- son to want to use less if they can and still feel assured they are getting adequate coverage and protection. Yet they are often frustrated when they seek advice. "Extension people can't make recommendations off the label," Polk said. Not only is there potential liability, but growers themselves can't afford to go off-label if they want companies to stand behind their products' performance. Still, growers can make adjustments that result in less active ingredient being applied per acre. Polk moderated a panel discussion on the ques- tion involving three Eastern fruit growers during the Mid-Atlantic Fruit and Vegetable Convention. The three are well known for their fruit growing proficiency. J.D. Rinehart grows 100 acres of peaches and 300 of apples near Smithsburg, Maryland, with his brother, John; Chris Baugher grows apples in Aspers, Pennsylvania; and Gary Mount and his wife, Pam, have 200 acres of fruits and vegetables they market directly from their farm, Terhune Orchards, in Princeton, New Jersey. The old way The standard spray recommendation was developed back in the days of large trees on seedling rootstocks. The recommendation for apples called for mixing the labeled rate of pesticide into 400 gallons of water, and that was to cover one acre to the point of liquid runoff. This was called a dilute spray, or 1X dilution. However, researchers found growers didn't need to haul that much water, and that fewer gallons could be used, so growers began using 2X, 3X, 4X, and 6X dilutions, cutting water to 200, 133, 100, or 76 gallons per acre—which would apply the label rate per acre in less water. But as trees became smaller, growers cut gallons per acre as well, and that reduced the amount of active ingredient applied per acre. It all became quite complicated. The Baugher way "We moved to high density incrementally," Chris Baugher said, "and that was not a good idea. Now we have all kinds of tree sizes and spacings, and we have to try to figure out how much to spray." Baugher said he starts with the advice given by the late tree fruit pathologist and entomologist Dr. Paul Steiner at University of Maryland. Steiner, who died in 2000, recommended growers apply 0.09 gallons of low volume spray, where droplets were very small, for each 1,000 cubic feet of canopy volume, and use 0.7 gallons per 1,000 cubic feet of dilute spray where larger droplets would be applied and trees wetted to the drip point. Baugher measured the height of the trees in various blocks, multiplying by the width of the trees and the length of the row. The calculations gave him a general idea of how much canopy he had to spray in different blocks. He found he could simplify things to four application rates. Using a 6X dilution, he sprays 50 gallons per acre "on my big old trees, same as Dad did," 36 gallons per acre on dwarf and semi-dwarf trees, 25 gallons per acre on young dwarf plantings in their third and fourth leaf, and 13 gallons per acre on new, non-bearing plantings. For peaches, he sprays everything 50 gallons per acre, 6X. Baugher also uses a Raven SCS-330 sprayer control system—"cheap compared to smart sprayers"—and can further adjust application rate on the go by changing ground speed between 2.3 and 2.8 miles per hour. The Rinehart way J.D. Rinehart uses a smart sprayer. "That eliminates a lot of the issues," he said. The smart sprayer turns nozzles on or off, as the tree height gets taller or shorter, and turns all the nozzles off if there is no tree in the space to spray. The sprayer operator drives at a consistent 3 mph. He has lowered the fan speed, reducing the power take-off speed from 540 revolutions per minute to 450, and uses a 3X dilution. That dilution provides enough water so he gets better protection against bacterial spot in peaches, he said. And the peach tree canopy volume is controlled by pruning all trees to ten feet tall. Matching the spray to the tree Spray guide offers tree row volume spraying tips T he 2015 New Jersey Commercial Tree Fruit Production Guide devotes six pages to the subject of applying sprays according to the volume of the tree canopy per acre. The guide generally follows the rules developed by University of Maryland horticulturist Dr. Paul Steiner in the 1990s. According to Dean Polk at Rutgers University in New Jersey, Steiner developed his tree row volume method after observing what worked for growers in the Mid- Atlantic States, and they were by then reducing tree size, reducing the dilution of sprays, and reducing the number of gallons of spray applied per acre. Steiner said growers should apply dilute spray at the rate of 0.7 gallons per 1,000 cubic feet of tree row volume or 0.09 gallons per 1,000 cubic feet of concentrate or low volume spray, and then cutting the amount applied per acre to a third or a half for trees with little or no foliage. "One way good coverage can be obtained is to use high-volume dilute sprays of 200 to 400 gallons per acre to thoroughly wet all target surfaces to a point where excess spray liquid drips to the ground," the spray guide says. "This is important where absolute coverage of all surfaces is required. Underdosing does not occur because all parts of the tree are thoroughly wetted. Overdosing does not occur because any excess material runs off." "For trees with a full canopy of foliage, a dosage volume of about 0.7 gallon per 1,000 cubic feet of tree row volume will usually reach the drip point." This rate, however, should be cut to a half or third early in the season. "An apple tree at green tip has approximately one-fifth the surface area it will have at full leaf," the guide says. Good coverage can also be obtained using low volume sprays of 25 to 60 gallons per acre—in which a fine mist of droplets are uniformly deposited without reaching the drip point, the guide says. "An LV rate of 0.09 gallon per 1,000 cubic feet TRV provides adequate coverage in most orchards under most conditions," the guide says. The guide does not recommend applying fewer than 25 gallons per acre. —R. Lehnert As canopy volume has decreased, growers would like to use less pesticide. by Richard Lehnert Gary Mount Chris Baugher