Over the past few years, herbicides with the active ingredient glufosinate (Rely, Rely 200, Rely 280) have become very important in California almonds as well as other tree nuts and grape vineyards.
Glufosinate is classified as a “Group 10, or Group B” herbicide an inhibits an enzyme important in the production of the amino acids glutamine in plants. Although it sounds similar to another amino acid inhibitor, glyhosate (the active in Roundup and others) glufosinate works quite differently than the Group 9 herbicide glyphosate. Click here for more mode of action information from WSSA.
I’ve discussed the differences between these two herbicide active ingredients with almond growers at a number of UCCE meetings and other venues as well as online at UCWeedScience like this post from (November 1, 2010) comparing the differences and similarities between glyphosate and glufosinate herbicides.
Because it has a different mode of action than glyphosate, glufosinate has become very important in California orchards and vineyards – especially those struggling with glyphosate-resistant weeds like horseweed (eg mare’s tail), hairy fleabane, ryegrass, and junglerice. Unfortunately, glufosinate (Rely 280) is going to be in very short supply in California during 2013 and possibly into 2014 so almond growers and pest control advisors should plan ahead if you are not already doing so.
This scarcity of glufosinate in California seems to driven by glyphosate-resistant weeds in other cropping systems in other parts of the country. The ai glufosinate in Rely 280 is the same ai used in Ignite, Liberty, Basta, Finale herbicides – several of these are used in LibertyLink crops such as cotton, corn, canola, and soybean as well as a few other crops. As well as being much larger markets (several hundred million acres) than CA trees and vines some of these cropping systems have much more serious glyphosate-resistant weed problems than we do. (search for glyphosate-resistant Palmer amaranth or waterhemp if you want a scare). Until production of the active ingredient can be ramped up to meet the national demand, most of the glufosinate will be sucked out of our markets in California in 2013 (the forecast for 2014 is not very optimistic either).
What should California growers do? The same thing they should be doing every year. Planning ahead, scouting fields, rotating herbicide modes of action, etc. This year (particularly since it’s looking like a good rain year) would be a good time to investigate some of the preemergence herbicides available. I shared our T&V herbicide registraton chart in a recent UCWeedScience blog post but you can also find it here.
Although I have not had time to update it as planned, the herbicide susceptibilty chart at WeedRIC is still a good resource as you plan weed management strategies for the coming season.
(Article originaly posted at UC Weed Science)