Herbicide Resistance Is Tough To Handle
January 6, 2015 Glyphosate is one of those materials that is almost too good for their own good, much like methyl bromide. When the original formulation of glyphosate, Monsanto’s Roundup, went off patent in the late 1990s, the price of generic products dropped precipitously.
The cost of an application became only $5 or $6 an acre, says University of California Cooperative Extension Weed Specialist Brad Hanson. Many growers, who like any other business people are always looking for ways to cut costs, began to use it almost exclusively.
“The grower said ‘It’s cheaper to spray (glyphosate) four times than to use a pricey pre-emergent (herbicide),” he says. “But because of that, resistance developed.”
Hanson was quick to add that glyphosate resistance was first found in the so-called major crops, such as corn, soybeans and cotton, but that was more a function of how the varieties were bred. “Our problems (in specialty crops) were due more to the low cost of glyphosate than the development of the GMO (genetically modified) crops,” he says.
To avoid resistance problems, growers must employ a variety of weed management approaches, says Hanson. He recommends that growers base their plan on a three-legged stool of sorts: Introduce herbicides that have differing modes of action; use not just chemical, but cultural approaches; and always be vigilant.
Use Pre-Emergents
It’s important for growers to use herbicides with differing modes of action to avoid resistance. Pre-emergent herbicides, for example, have completely different modes of action than do post-emergent herbicides such as glyphosate. “We don’t see a lot of resistance to pre-emergent herbicides,” he adds.
There are a wide variety of products available to growers, says Hanson , as there are about 20 different modes of action among all the various herbicides. While only about six to eight are available for a given crop, including both pre- and post-emergent formulations, that still gives growers a good selection from which to choose.
“By introducing additional modes of action, the likelihood of weeds’ surviving is low,” he concludes.
A diversified approach doesn’t just refer to diversity in herbicides, however. Hanson says a grower could employ tillage, whether in lieu of or in addition to an herbicide application.
Be Vigilant
It’s been said that those who fail to plan, plan to fail, and so it is with a field scouting plan for weeds, says Hanson. You want to formulate a plan, implement the plan and assess it following harvest. “If you can control weed problems when they’re small,” he says, “you can save a lot of money.”
That’s because of the nature of weeds, which are programmed to reproduce. One horseweed can have an astounding 400,000 seeds per plant, he says, and while not all weeds are that prolific, they are generally good at propagating their species.
If you think it’s necessary to send a hand crew to get rid a particularly stubborn outbreak of a given weed, do it, because that one hand crew could potentially save you thousands of dollars over the ensuing decades.
“Do not let that plant go to seed or you could have generations of weeds to deal with,” he says. “There’s an old saying: ‘One year’s seeding equals seven years’ weeding.’”
Subscribe Today For
