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• With well over 100,000 acres of cotton and about a half million acres of soybeans planted this year in Virginia, concern is growing among producers as to the best tools available to manage Palmer amaranth and other herbicide tolerant weeds.
“I have one grower who knew going into this season that he had some fields with glyphosate resistant pigweed. So, he planted LibertyLink cotton in these fields. He put on Reflex behind the planter and then came back with two applications of Ignite. As of mid-July those fields were very clean — the combination did a great job,” Cooper says.
The veteran Virginia consultant says one of the keys to using the LibertyLink system is to use a herbicide like Reflex to keep fields clean until they can be sprayed with Ignite.
Cooper stresses the importance of following the label, particularly to avoid spraying Ignite on cotton that is blooming. The herbicide can cause cotton blooms to abort and the result will be significantly lower yields, he explains.
Reflex is a post-emergence contact herbicide that is activated by exposure to sunlight to form products that destroy plant tissue by rupturing plant cell membranes. The destruction of cell membranes results in a rapid browning of plant tissue in target broadleaf weeds.
The primary active ingredient in Ignite is glufosinate. The way it kills weeds is similar to glyphosate, but its mode of action and chemistry are different. Both modes of action are different from Reflex.
Still, long-time North Carolina State University Weed Scientist Alan York, a pioneer in the study of glyphosate resistant pigweed, says growers need to remember the lesson learned from over-use of any herbicide.
Ignite, or glufosinate, is the best single option we have now to manage resistant pigweed, but over-use will likely put us in the same situation we found ourselves in back 2004-2005 with glyphosate resistant pigweed, York warns.
Increased cotton acreage in Virginia, with many growers having little experience growing the crop, increases the chances for over-use. It’s tempting to over-use a product that will kill pigweed, marestail, ragweed and volunteer soybeans from Roundup Ready soybeans grown the previous year.
Cooper says Ignite did a consistently good job of killing pigweed that were four inches tall or smaller. When weeds got six or more inches tall, it seemed to kill some weeds and didn’t kill others. “I just don’t feel comfortable killing pigweed more than four inches tall with Ignite,” Cooper says.
An advantage of using Ignite in LibertyLink cotton is that you can come back with a second, sometimes a third spray to manage bigger pigweed.