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W i n e s & V i n e s s e P T e M B e R 2 0 1 4 55 Roncoroni considers horse- weed (Conyza canadensis) (often called mare's tail) and panicle willowherb (Ebilobium bracycar- pum), both relatively new to the area and his biggest challenges at present. Willowherb can grow to 5 feet tall, getting into the clus- ters and even interfering with mechanical harvesting. It isn't resistant to glyphosate but tolerates it. Glyphosate can kill the top of the plant, but the weed will simply grow out from lateral buds. "It's really become a problem," he said. It is killed by some pre-emergent treatments. Horseweed (the preferred name) has gone from tolerance to resistance to glyphosate in the San Joaquin Valley. "It ger- minates almost year-round, so it can crop up if you water after harvest," Roncoroni said. He said that it was relatively new in Napa Valley, and it's a real problem. "It can be 0.5 inches in diameter and 6 to 8 feet tall. It uses a lot of water and can inter- fere with harvesting." Fortunately, Matrix, Chateau and Alion are very effective in killing it, and the first two have some post-emergent effective- ness. "If it germinates in the fall, you need post-emergent herbicide to kill it." Glyphosate will only kill small plants (4-5 inches tall). Rely can control both horse- weed and willowherb, but again only when they are rela- tively small. Roncoroni added. "The only thing that will kill large willow- herb or horseweed is iron—hard- ened on the end of a handle.' Roncoroni noted that the pre-emergent herbicides aren't effective against field bind- weed (Convolvulus arvensis), which has very deep rhizomes. It is best controlled with spot application when the morning- glory relative is blooming. This may take several years once established. Turkey mullein (Croton se- tigerus) is a common weed, but Roncoroni says it isn't a big water user and doesn't grow very big so it isn't a real problem. It prefers uncultivated soil, which is common in vineyards. Roncoroni's trials showed that some of the new herbicides are very effective against weeds including tenacious types, but he noted that he didn't have information about price. Some like Alion are so new that other weeds may prove resistant to them in the future, but most re- sistance has been found recently in the overuse of post-emergent herbicides by themselves. Organic herbicides Roncoroni didn't include any organic herbicides in the trials since no new ones have been approved recently, though he expects some soon and will con- duct trials with them. He fears, however, that they may be ex- pensive and not effective against tough weeds. —Paul Franson "Any weeds on the vineyard floor are using water that's not going to be available to the crop," Hanson said. "Growers who are very, very concerned about water are saying, 'Y'know what, maybe I should kill all of that with tillage or herbicide applica- tions because I can't afford to have that weed using water." Knowing how to control weeds without making them stronger makes it important that growers follow good man- agement practices when they go about conserving water. Back in the Okanagan, Sapsford will continue to work toward that, discussing his findings with local agrono- mists. He spoke at a profes- sional development event this past March and will also address a workshop at the University of British Colum- bia's campus in the Okanagan this month. PROVIDING SOLUTIONS TO THE WINE INDUSTRY To order your copy: Ph: + 618 8369 9509 E: orders@winetitles.com.au Visit: www.winebiz.com.au Australia & New Zealand Leading Industry Directory PLUS + Statistics + 2014 Overview + Calendar of events + Wineshows + Courses + Organisations • 7,000 Industry listings • 9,000 Personnel • 3,100 Wineries • 4,800 Wine brands • 1,500 Grapegrowers • 2,200 Buyers' guide listings • 280 Distributors & retailers • 180 Writers & media IN PRINT & ONLINE NEW 2014! & account listings G R A P E G R O W I N G