What is in this article?:
- Almond industry sets crosshairs on weed resistance
- Managing weed resistance
- A top concern and increasing challenge for any effective weed control program is resistance management. Glyphosate resistance is now seen in populations of horseweed, hairy fleabane (a strain of this weed is now also resistant to paraquat), both Italian and rigid ryegrass and junglerice.
- Growers attending last year’s Almond Conference heard an update on almond weed management from UC Extension weed specialist Brad Hanson that not only provided new information but also solid basics and online resources to fine-tune weed management for the most effective control program.
An effective preemergence herbicide program provides an important opportunity to rotate herbicide modes of action for resistance management and may be economically competitive with multiple applications of burndown herbicides. The center plot was treated with two applications of glyphosate while the surrounding plots were treated with Alion or Pindar GT.
Growers attending last year’s Almond Conference heard an update on almond weed management from UC Extension weed specialist Brad Hanson that not only provided new information but also solid basics and online resources to fine-tune weed management for the most effective control program. Hanson’s work in almonds is funded by the Almond Board of California (ABC).
(For more, see: California tree nut crops on fast track)
Hanson started his talk with a look at the basics of effective weed control in almonds and some available online resources. These are the steps he recommends:
Correctly indentify weed problems. Hanson pointed out a valuable online resource that he called “weed ID for dummies.” It is the Weed ID Tool, which can be found on the UC Davis Weed Research and Information Center (WRIC) website at http://wric.ucdavis.edu. Another valuable resource is the Almond Weed Photo Gallery on the UC Statewide IPM website, www.ipm.ucdavis.edu.
Select registered herbicides with the proper weed spectrum. Hanson annually updates almond herbicide registrations; the list can be found at the UC Davis WRIC website mentioned above. Go to Weed Control Quick Link, choose Information by Crop or Topic, then Tree and Vine crop registration. With respect to weed susceptibility, Hanson pointed to a number of valuable online tools. These include the weed susceptibility chart found on the UCD WRIC site and the charts for susceptibility of both winter and spring/summer weeds to herbicide control on the UC IPM web page for almonds.
Hanson noted recent changes in almond herbicide registrations. They are:
- Gallery, previously registered only for non-bearing trees, has been rebranded as Trellis (isoxaben) and can now be used on bearing almonds.
- Matrix (rimsulfuron) is now off patent and generic labels are anticipated.
- Pindar GT (mixture of oxyfluorfen and penoxsulam) and Alion (indaziflam) are recently registered. Both herbicides have a broad weed spectrum, including both grasses and broadleaves.
- Rely (glufosinate), active on both grasses and broadleaves, has a new formulation (Rely 280.
- Venue (pyraflufen-ethyl), primarily active on broadleaf weeds, can now be used in-season.
Properly apply materials using calibrated equipment, with correct timing at the appropriate weed growth stage. Applicators must also be properly trained.
Hanson highlighted several key factors for the most effective weed control program. He said programs should be tailored to your needs, not your neighbor’s. It is important to scout and ID weeds in your own orchards. Don’t forget areas that are not mowed or sprayed, as these are reservoirs of weed seed and future weed problems. It is also important to scout fields after applications to follow up on escapes or other problems.
He emphasized the importance of putting the herbicide on target. For residual herbicides, the goal is to move the material into the zone of seed germination, which is the top ½–¾ inch of soil. Blow berms before application and treat ahead of rain or irrigations. For postemergence herbicides, remember large weeds and weeds that are water-stressed are harder to control. It is important to use appropriate surfactants for penetration, retention or water conditioning (e.g., ammonium sulfate for hard water).