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 AlmondBoard.com/Farmpress27.