nov-dec-2019

Weed Control Strategies Dr. Brad Hanson, UC Cooperative Extension Weed Science Specialist, held a richly informative seminar at the Blue Diamond Growers Annual Meeting. Hanson emphasized the common phrase “the right tool for the job” in his seminar when he stated, “Often, when I get a question about poor performance of a weed control program it’s because the grower is using the wrong tool for the job.” He explained that what typically happens in those situations is that the weed is not properly identified, a good control plan is not in place, and the wrong material is being used. The result is poor control or no control at all. Current Practices A typical almond orchard is strip-sprayed three to four times a year, usually with glyphosate. While glyphosate use has not decreased, for about six years, growers have been using increasing amounts of pre-emergent material, and there has been a troubling increase in resistance to glyphosate and other popular products. In addition, there is a growing resistance in many weeds, not only to glyphosate, but also to other widely used products. Some of the most troublesome weeds, such as fleabane, horseweed, Palmer amaranth, rye grass, annual bluegrass and jungle rice, are showing resistance to glyphosate. Fortunately, Hanson mentioned that there are many tools for controlling winter species of weeds. Winter weeds include horseweed, annual bluegrass, fleabane and ryegrass. Summer species of weeds are more of problem. Most are resistant to glyphosate and paraquat. To deal with resistance, Hanson suggests spraying the newly emerging weeds with glyphosate when no more than an inch or so across. “That may control them,” he said, “but waiting any longer will not. If you have a sensitive population and let them get six inches across and starting to bolt, you will not likely be able to control them.” Timing is important. Treat new growth early regardless of the species sensitivity to herbicides. Pre-Emergent Programs Hanson has experimented on how to manage resistant species and what kind of treatment regimen would maximize control. He found that applying a product like Alion in winter followed by Prowl in spring just before weeds emerge, and another application in August could give better control. He and a graduate student ran orchard trials with variations of this approach with good results. ANNUAL GROWERS MEETING 3 0 A L M O N D F A C T S