Issue link: https://read.dmtmag.com/i/662797
www.goodfruit.com Good Fruit Grower APRIL 15, 2016 23 In the Pacific Northwest, growers look- ing to control horseweed in new vineyard plantings are limited to Trellis (isoxaben) or Goal (oxyfluorfen) as treatments before horseweed emerges and to glyphosate after the weed begins to show, according to Dr. Drew Lyon of Washington State University's Department of Crop and Soil Sciences. In established plantings, Northwest growers have a list of compounds they can try pre-emergence: Karmex (diuron) and similar brands, Alion (indaziflam), Solicam (norflurazon) and Princep (simazine). Post-emergent applications include Aim EC (carfentrazone), Rely (glufosinate), Roundup, Venue (pyraflufen) and Gramoxone Inteon (paraquat), Lyon said. Several other products provide pre- and post- emergent control of horseweed in established plantings. These include Chateau (flumioxazin), Goal and Matrix (rimsulfuron). Alion and Matrix can be tank-mixed to provide pre- and post- emergence control as well. Northeast growers looking to control seed spread should try a post-emergent application of Rely or Aim EC, Senesac said. Contact herbicides like Gramoxone are also an option. But Senesac said he's found that the best means to control horseweed is Alion, the relatively new herbicide introduced to the market in 2013. It can be used on grapevines established five or more years. Alion inhibits cellulose biosynthe- sis, preventing cell walls from forming in plants, disrupting seedling development. It has very low volatility and low leaching potential. "It can be applied anytime of the year on unfrozen soil," he said. "Its plant-har- vest interval is 14 days." Senesac said there are two reasons growers should consider using the compound. One is the environmental load nec- essary to achieve control is very low; its application rate is 3.5 to 5 ounces per acre or .045 to .065 pounds per acre-inch. "That's the equivalent weight of four to six nickels," he said. The second reason is its staying power. "It has the potential to remain active with a spring application long enough to inhibit horseweed seed germination into late summer and beyond," Senesac said. Organic growers, meanwhile, can use Scythe (pelargonic acid) or Suppress (caprylic and capric acids), which is labeled for most food crops, including grapes. Senesac plans to run trials on Suppress this summer. Field trial In response to grower concern about Alion's effect on between-row cover crops, Senesac conducted a field trial. He seeded several field-grown ornamental plots with buckwheat 13 months after an Alion and Chateau (flumioxazin) application. At 2.8 fluid ounces, a rate just below the labeled grape rate, and six weeks after seeding, 58 percent of the cover remained. At 8 ounces per acre, Chateau left 54 percent of the cover crop. "Neither prevented adequate establishment of buckwheat," Senesac said. At lower rates, growers should not experience problems planting cover crops the following year, he said, though applying the compound at higher rates may prove otherwise. • 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.