Issue link: https://read.dmtmag.com/i/662797
20 APRIL 15, 2016 Good Fruit Grower www.goodfruit.com G rape growers tend to base weed control choices on what they used successfully in the year of their best yields. They may vary those choices somewhat to account for specific problems their scouts turn up, but usu- ally there are two or three compounds they use year after year. Instead of finding continued success and high yields, those "tried-and-true" weed control compounds are bringing two other things to vineyards: herbi- cide-resistant and herbicide-tolerant weeds. When weeds are suppressed but not controlled — plants are partially wilted, for example — it usually means the weeds are naturally less sensitive to a control measure or herbicide-tolerant. Herbicide resistance, meanwhile, is a plant's inherited ability to survive following exposure; resistance may be naturally occurring or a result of genetic engineering. Over time, the few resistant plants can multiply into a much larger population. It's a natural process, virtually the same as drug resistance. The longer a herbicide is on the market, the longer the list of resistant weeds. For example, according to the International Survey of Herbicide R e s i s t a n t W e e d s , t h e r e a r e 3 5 known weeds resistant to Roundup (glyphosate). The site also reports 11 herbicide-resistant weeds found specif- ically in vineyards. Tolerant and resistant species can develop in a vineyard in one region of the country and find their way to others hundreds of miles away. "Some seed, like horseweed/marestail, can fly very far," Dr. Andy Senesac, Cornell University/Long Island Extension weed specialist, said at the Mid-Atlantic Fruit and Vegetable Convention in Hershey, Pennsylvania, this winter. The best protection against resis- tance is to monitor vineyards after treatment. "If a post-emergent was used, look for a single, slightly injured or uninjured weed species," Senesac said. "With pre-emergents, watch for a single species appearing soon after application." Late summer is prime time for spot- ting resistant species, Senesac said. Growers should look for the sudden Herbicide resistance a growing conceRn Grapes Researcher offers tips for helping to control weeds in vineyards. by Dave Weinstock "If a post-emergent was used, look for a single, slightly injured or uninjured weed species. With pre-emergents, watch for a single species appearing soon after application." —Andy Senesac