Good Fruit Grower

October 2016

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Page 18 of 47 Good Fruit Grower OCTOBER 2016 19 PHOTO BY CARL ROSEN Preliminary results from the nutrition study suggest that whole-leaf sampling may be a better gauge of tissue- nutrient level than the common technique of sampling only the petiole. Here, a leaf is separated into blades (left) and petioles (right). For instance, copper and sulfur have been used as fungi- cides for centuries, but both are known to cause injuries to some of the European wine grape varieties. "The issue with northern cultivars is there's a whole lot less known about them, because most just haven't been around very long. In fact, if you look at extension literature on cop- per and sulfur phytotoxicity, the columns next to these cold-climate varieties are filled with question marks," she said. For the study, McManus' group monitored 15 cold-cli- mate varieties in two Wisconsin vineyards over four years. One vineyard is in Door County, which is on a peninsula that juts out into northern Lake Michigan and gets the big lake's moderating influences, including later springs and cooler summers. The other vineyard is in Madison, which is located inland in the southern part of the state. Vines at the two sites were randomly selected each season to receive biweekly treatments with one of three types of fun- gicides — copper, sulfur, or a newer product called difenoconazole, which has been available for a few years — or to receive no fungicide. The researchers regu- larly checked the vines for marginal browning, speck- ling or any other potential leaf injuries and ranked the amount of visible damage. Among the results: —As expected, Maréchal Foch and the related culti- var Leon Millot showed high sensitivity to sulfur. "Those two varieties are older ones that have been around for decades, and we knew going into the trial that they had sulfur sensitivity," McManus said. —Brianna, which experienced minor injury from sul- fur, showed significant damage when treated with cop- per. "Brianna was the most sensitive to copper of all 15 varieties to the point that in some of our trials, just one or two sprays to Brianna with the copper fungicide caused a reaction," she said. —None of the tested varieties showed a negative response to difenoconazole, even though the labels "One of our main goals is to remove some of those question marks in the extension literature and replace anecdotal observations with real scientific data." —Patricia McManus Safe and Effective Plant Nutrients and Biopesticides ® Botector ® Blossom Protect ™ ® ® ® ORGANIC ® ORGANIC Herbicide EC ®

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