Davis, Calif.—As if it’s not tough enough for grapegrowers to keep up with the latest insects and other pests, they may have trouble finding an important herbicide this year. Brad Hanson, cooperative extension weed specialist for the University of California, Davis, Department of Plant Sciences, reports that glufosinate (Rely 280) is going to be in very short supply in California during 2013 and possibly into 2014.

“Over the past few years, herbicides with the active ingredient glufosinate have become very important in California grape vineyards. Growers and pest control advisors should plan ahead if you are not already doing so,” Hanson warns.

Glyphosate vs. glufosinate
He stated that though the names are similar, glufosinate works quite differently than another amino acid inhibitor, glyphosate (the active ingredient in Roundup and others, which is classed as a Group 9 herbicide.

Glufosinate is classified as a Group 10 (or Group B) herbicide, which inhibits an enzyme important in the production of the amino acids glutamine in plants. A very technical explanation of the differences is available here.

In simpler terms, glyphosate (Roundup, Durango, Honcho) inhibits EPSP synthase (EPSPS) enzyme.

Glufosinate (Rely, Rely 200, Rely 280) inhibits glutamine synthetase enzyme.

Additionally, glyphosate translocates easily through the plant, while glufosinate doesn’t, and it’s critical to provide good coverage.

However, resistance to glyphosate has been reported in California among such weeds as ryegrass, horseweed (mare's tail), junglerice and hairy fleabane, while no resistance to glufosinate has been reported in California so far, making it an alternative method of weed control.

Hanson noted that because it has a different mode of action than glyphosate, glufosinate has become very important in California vineyards, especially those struggling with glyphosate-resistant weeds.

Demand for glufosinate
Hanson said that the scarcity of glufosinate in California seems to caused by demand for use with other crops elsewhere.

“The AI (active ingredient) in glufosinate in Rely 280 is the same AI used in Ignite, Liberty, Basta and Finale herbicides used in crops with the LibertyLink genetically-modified trait as the only nonselective alternative to glyphosate-tolerant systems with crops such as cotton, corn, canola, and soybean.

“As well as being much larger markets (several hundred million acres) than California trees and vines, some of these cropping systems have much more serious glyphosate-resistant weed problems like glyphosate-resistant Palmer amaranth or waterhemp than we do here,” Hanson observed.

He stated that until production of the active ingredient can be increased to meet the national demand, most glufosinate will go to other states in 2013 and possibly 2014.

To deal with the problem, Hanson reminds growers to do the same thing they should be doing every year: “Plan ahead; scout fields; rotate 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 pre-emergent herbicides available.

He added that another glufosinate product, Reckon 280SL from Solara, may be available to some extent as an alternative in California.

Read more at plantsciences.ucdavis.edu.