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 Another valuable resource is the Almond Weed Photo Gallery on the UC Statewide IPM website,

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:

Pre-emergence herbicides:

  • 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.

Post-emergence herbicides:

  • 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).

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. As with diseases and insects, it is important to develop and use resistance management programs for weeds. This includes not overusing herbicides with the same mode of action (avoid making three or more applications of the same herbicide or herbicides from the same group during the season), rotating herbicides having different modes of action, and using tank-mix partners with different modes of action (this, of course, also broadens the spectrum of weeds targeted). Herbicide mode of action is noted both on the registration update provided by Hanson on the UCD WRIC website and on the UC IPM Almond Herbicide Treatment tables.

Hanson noted that because of glyphosate resistance, herbicides like Treevix (saflufenacil) and Rely are gaining in use because they control some of the resistant weed species. He said that although Rely is used as a burndown herbicide, it can translocate to some extent, thus careful calibration and application are recommended to avoid potential damage to almonds. He is conducting research on managing the use of Rely and developing guidelines. For more information detailed in his conference poster, go to the link below. A comparison of burndown herbicides (glyphosate, Rely and paraquat) is given in Hanson’s presentation, which can also be found at the link.

Lastly, Hanson said it is important to consider the cost-benefit of different herbicide and management options. For instance, residual herbicides providing longer control may have more value than repeated burndown applications.

To view Hanson’s full presentation, as well as additional resources and links mentioned here, go to