Issue link: https://read.dmtmag.com/i/657340
www.goodfruit.com GOOD FRUIT GROWER APRIL 1, 2016 39 "We keep telling the growers it's nec- essary," he said. "A lot of them don't think so, and then they don't get the return bloom." It's most important in the northern part of the state, where soil is sandy, he said. Perry estimates that about 40 percent of tart cherry growers and more than half the grape growers in northwest Michigan use micro-irrigation. South- ern Michigan apple growers, with fewer high-density orchards, more easily get away without it, he said. Perry recalls trials from 1984 that showed irrigation brought a 20 percent to 25 percent increase in yield and return bloom and a 15 percent to 20 percent increase in fruit size. Irrigation is becoming more important in the East as growers switch to high-den- sity trees on dwarfing rootstocks with shallower root zones, Alan Lasko of Cor- nell University told growers at the IFTA conference. To help them, researchers have developed a mathematical irriga- tion model specifi c to apples in Eastern climates, because Western guidelines don't always add up, Lasko said. Irrigation models normally use the Penman-Monteith equation, which estimates the effects of weather on plant water loss, using the water use of grass as a baseline. Modelers then assume their plant — in this case an apple tree — uses a consistent fraction of that amount, called a crop coeffi cient. That seemed to work in desert climates such as eastern Washington and California's Central Val- ley, but not so well in upstate New York, he said. Using the new Cornell model, trials in the Hudson Valley of New York showed a decrease in fruit stress and increase in fruit size compared to no irrigation, Lasko said. Lasko and his colleagues have posted the tool online in conjunction with the Northeast Regional Climate Center. It asks growers to choose a nearby weather station and then input some specifics about the orchard, such as the age of the trees, to receive irrigation information. • ONLINE The Cornell University apple-speci�ic irrigation model can be found at newa.nrcc.cornell.edu/newaTools/apple_et.