Good Fruit Grower

May 15

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"Growers in the Northeast have lost thousands of Macoun trees to the basal trunk cankers that were described in 2004." —David Rosenberger Indiana scientist expressed his concern that glyphosate was reducing ability of crops to resist disease. Rosenberger began studies to see whether glyphosate-treated apple trees showed higher incidence of fireblight and also to see if glyphosate was related to internal browning problems that developed in some apples, notably Empire, after long-term storage. Glyphosate is known to work by tying up key minerals important to the shikimic acid pathway essential for respiration in plants. He has since concluded that glyphosate exposure does not contribute to higher levels of fireblight, and he has not been able to show that it causes internal browning. Results have been "inconsistent and unpredictable," he said. "Observations in commercial orchards suggest that repeated exposure of tree trunks to glyphosate can lead to development of basal trunk cankers, and drift to foliage can make trees more susceptible to winter injury," he said. "However, glyphosate did not affect susceptibility to fireblight in two years of replicated trials, and it increased the incidence/severity of internal browning in Empire apples in only three of ten trials." • David Rosenberger is in charge of the plant pathology program at the Hudson Valley Lab in New York, and is the overall administrator of the experiment station. The fine droplets can remain airborne for a long time and will almost certainly drift onto trees. Never apply glyphosate to Macoun trees. This variety seems uniquely susceptible to damage if glyphosate hits the tree trunks near the soil line. Some growers and consultants believe that protecting trunks with white latex after planting can reduce the potential for herbicide injury, but this claim needs to be verified in replicated trials. Rosenberger began studying glyphosate's possible effects on apple trees in 2003, with his extension colleague Mike Fargione, after basal trunk cankers were seen on trees where herbicide was applied with boom sprayers. For Rosenberger, what might have been an "herbicide issue" became a "plant disease issue." "Since that time, growers in the Northeast have lost thousands of Macoun trees to the basal trunk cankers that were described in 2004," he said. The role of glyphosate in formation of the basal cankers was never proven, although it appeared that glyphosate predisposed the bark to invasion by Botryosphaeria dothidea, a canker fungus. But Rosenberger also noticed that lower limbs on trees sometimes died of what looked like winter injury while limbs higher up survived, and he suspected the cause was injury from glyphosate drifting upward from spray applied at ground level. Then, in 2009, researchers in Ohio reported high incidence of trunk cracking in ornamental nursery trees where glyphosate was used for weed control, and an QUALITY FRUIT DESERVES A QUALITY RIDE! 8 9 Air-ride suspension conversions Flatbed re-arching, re-decking, shortening and air hitches. Hydraulic lift conversions. New and used straddle trailers, all sizes. New and used parts. Repairs and custom fabrication. CARRIER TRANSPORTS, INC. STRADDLE TRAILER MANUFACTURING AND REPAIR 509-452-0136 After Hours: JIM KUNZ 509-949-5904 GOOD FRUIT GROWER May 15, 2013 41

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