Issue link: https://read.dmtmag.com/i/590163
www.goodfruit.com GOOD FRUIT GROWER NOVEMBER 2015 45 irrigation should be available. A dry season after root pruning can really hurt apple size. The Phil Brown machine has blades at the end of arms that can move in or out hydraulically. The "rule of thumb" seems to be to set the blades to cut at full depth, 14 inches, at a distance from the tree of about three times the trunk diameter. That would put the blade 18 inches away from a six-inch tree. A skid plate behind the blade closes the slot in the ground. Brown, who builds the root pruner and has sold units in Michigan and New York, summarized its effects this way: "The main thing, it controls the size of the tree. It'll enhance color and make a firmer apple. It also downsizes the fruit a little bit, and some fruit is just too big. It slows tree growth and saves a lot of pruning. On over-vigorous ground, it's like going to a smaller rootstock. "If you have a freezeout year and no fruit to hold back the vigor that year, root pruning can help," he said. "It's hard to pull," Tom Rasch said. "It sometimes takes two tractors." Fruit growers often don't have the large tractors field crop growers have, however mainly it is stability more than power that's needed. The lead tractor serves to keep everything in line. Rasch's one-row pruner's blade runs under the tree, to the right side of the tractor, so the tractor wants to pull right. The two-row pruner runs straighter, but it takes more power. Chuck Rasch uses a 100-horsepower four-wheel-drive tractor to pull his. Brief history Michigan State University horticulturist Ron Perry used a root pruner last year to try to restrict the size of Montmorency tart cherry trees to make them harvest- able with an over-the-row berry harvester. In searching the literature, he noted there was a lot of research and interest in the practice several years ago. "The practice became popular when apple growers were using semi-dwarfing rootstocks and finding that trees were shading neighboring trees due to tight spac- ing," he said. "Studies have demonstrated that restricting root extension and volume by pruning with a sub-soiling knife can reduce canopy volume and vigor of fruit trees by nearly 30 percent." Tart cherries are not currently grown on dwarfing rootstocks, so trying root pruning seemed like some- thing worthwhile. A problem is the practice reduces the Montmorency fruit size about 20 percent, just as it does in apples, but that's undesirable in cherries. "We are seeing excessive stress for tart cherries when pruning is accomplished in bloom compared to during the pit hardening period," Perry said. He is cur- rently determining the optimum time to root prune for high-density tart cherries. Perry noted that interest in root pruning began in the early 1990s, just as growers were making other changes. "Several Michigan growers purchased an implement and in fact hardly used it as they were making the transition to vertical axe and slender spindle on M.9 stocks," he said. "Usage went dormant except for guys like Tom Rasch, who loaned me his machine for my cherry work in southwest and northwest Michigan. Tom still has sig- nificant acreage on MM.106 in multirow beds, which is why he uses his annually." Why the resurgence? "I believe that most of the inter- est lies in growers, especially on the ridge, transitioning to tall spindle systems at 3-by-10 (foot) spacings and wanting to develop wall systems with summer prun- ing," Perry said. "The challenge is that some of the soils are a little fertile and some varieties like Jonagold, Fuji, and Gala can be fairly vigorous and can challenge these spacings. "Secondly, one of the results of root pruning is a 15 to 20 percent fruit size reduction with increased color. For Honeycrisp, this is a benefit." • GREAT LAKES EXPO FRUIT, VEGETABLE AND FARM MARKET MICHIGAN EXPO GREENHOUSE GROWERS ON LI N E R EG ISTRATION SE PT. 28-NOV. 18 WWW.GLEXPO.COM R EG ISTE R BY NOV. 18 TO SAVE REGISTRATION COVERS BOTH CONFERENCES AND THE TRADE SHOW DEC. 8-10, 2015 GRAND RAPIDS, MI DEVOS PLACE CONVENTION CENTER AND THE AMWAY GRAND PLAZA HOTEL WWW.GLEXPO.COM 4,200 + attendees | 70 education sessions and workshops | 450 + exhibitors Pre-conference events on Dec. 7: Farm Market Bus Tour and National Vegetable Grafting Symposium