As with any other new technologies, there are pluses and minuses when farmers start putting the new traits or products on the ground or – in some cases – in the air, says Donnie Miller, weed scientist with the LSU AgCenter’s Northeast Research Station.
The plus with the new Roundup Ready Xtend and Enlist cropping systems is they work very well in controlling weeds, especially if they are properly supported with residual and other postemergence herbicides with different modes of action. The problems occur if they drift on to crops that don’t contain the resistance trait.
“To this point, we’ve talked about the plus,” says Dr. Miller, speaking to participants in the Northeast Station’s annual field day. “That’s including your residuals in there, including other modes of action to help us not only with the control we achieve, limiting the competition and also our resistance mitigation.
Unlike in the past, the labels for the new herbicide formulations that can be sprayed on Roundup Ready Xtend cotton and soybeans or Enlist soybeans will be filled with specific language when they are approved by EPA. Most observers believe that will occur before the 2016 growing season.
Language such as sprayer speed, height of the boom above the crops, specific nozzles to use, wind speeds in which they can be applied. “Those need to be followed as much as possible,” Dr. Miller said. “It’s like any other herbicide. When you apply them in less than ideal environmental conditions, you can get off-target movement.”
In test plots at the Northeast Station, researchers applied three different “drift rates” to demonstrate what can happen when the two herbicides in the new technologies wind up on crops that do not contain the resistance trait.
The most severe drift can occur when growers fail to clean out a spray tank properly and the residue from the previous herbicide gets on a non-target crop. Miller refers to this as the one-tenth rate of drift.
Simply allowing a herbicide to drift on to a non-target crop when wind conditions are not optimal would be somewhat less severe, a situation weed scientists might refer to as a one-hundredth rate. In cases of herbicide volatility, weed scientists might refer to that as the one-thousandth rate.
All three of those rates were sprayed on conventional crops and the crops rated for herbicide injury.
“No one wants herbicides drifting on their crops, but with the new technologies it’s better to have drift earlier than later,” says Miller. “Getting drift on soybeans during the reproductive stages is definitely more damaging than during the vegetative stage. But it would be better to avoid it all together.”
For more information on herbicide drift, visit http://herbicidesymptoms.ipm.ucanr.edu/HerbicideDamage/.