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October 2016

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Weed resistance: Not just an issue for agriculture

By Homer Deckard, IVM railroad vegetation control specialist, Dow AgroSciences

Homer_deckard You’ve no doubt heard about the issues the agricultural industry has had with glyphosate-resistant weeds hurting crop production. And while new technology such as the Enlist™ weed control system is changing that, many years of glyphosate use (and overuse) allowed certain tough weeds to build resistance, leaving many farmers concerned about the rapid growth of tenacious new resistant weeds.

But weed resistance extends beyond just farmers’ fields. It’s also becoming prevalent in the Industrial Vegetation Management industry. In fact, there’s been a dramatic increase in the scope and number of species of resistant weeds. If we don’t work as an industry to address the issue, our utility and pipeline rights-of-way, railroad properties and roadsides could be overtaken by resistant weeds like kochia, Russian thistle, Palmer amaranth, pigweed and others.

The history behind the problem
To understand how we’ve reached this point, you have to look back a couple of decades. Prior to the 1990s, many in the vegetation management and railroad industry relied mainly on proprietary herbicide products, which were — at the time — herbicides like glyphosate, sulfometuron and diuron.

In the 1990s, generic herbicides flooded the market, dramatically driving costs down, while industry expectations in terms of weed control remained the same. Lower costs led to the use of higher rates of these herbicides in many cases, and coupled with little to no rotation to herbicides with different modes of action, we’ve seen a tremendous spike in weed resistance, making these old standbys less effective in many situations. I’ve seen this especially in the railroad industry.

Consider that in 1990, a vegetation manager may have been able to treat an acre with 5 pounds of herbicide and get near 100 percent control of certain species. Then, in 2000, maybe it increased to 10 pounds of herbicide to get 70 percent control. Today, that herbicide may be totally ineffective on certain resistant species — no matter what rate is applied. In that case, the resistance has now become so specialized that you can’t just add more herbicide to achieve the same levels of control.

Be more forward-thinking
The answer is to incorporate innovative herbicides with different modes of action into traditional tank mixes. For example, only a decade ago, vegetation managers were seeing significant resistance issues in treating marestail (horseweed). Aminopyralid-based herbicides such as Milestone® specialty herbicide entered the market, providing an effective new tank-mix option, and the problem was easily solved.

It’s important to rotate herbicide programs from year to year to help address resistant species. Do these two things and you’ll gain significantly better weed control, you won’t be contributing to resistance and, over time, you’ll use less herbicide per acre, which is good for the environment and the long-term budget. While costs per treated acre may rise initially, rotating your programs will significantly extend the life of the current herbicide toolbox we have available to us as an industry.

Don’t resort to simply raising application rates of herbicides that are failing. This only accelerates resistant weed issues. Twenty years ago, resistant weed species could be counted on one hand; today, there are hundreds, mainly due to the use of the same herbicides year after year and increasing the rate as control declined.

Consider more forward-thinking solutions as you develop your vegetation management plan. It’s time the industry banded together to fight the potential for herbicide resistance in weeds on rights-of-way.