Iowa Public Television


Farmers Battle New Enemies in the War on Weeds

posted on May 4, 2012

As he announced nearly $200 million in grants from his foundation this week, philanthropist Bill Gates called on the United Nations to become more efficient in helping poor farmers and to set up a kind of accountability "report card" system for countries receiving aid.

Gates is a proponent of high-tech — and to some critics controversial — solutions for boosting agricultural productivity, including supporting genetic modification in plant breeding as a way to fight starvation and malnutrition.

Others, however, aren't so sure.  And some point to glyphosate-resistant weeds as evidence of a biotech boondoggle.  But just as brokers advise their clients to diversify their portfolios to minimize risk, scientists advocate a multifaceted attack to whip the weeds. David Miller explains.     

For centuries farmers have waged war on weeds. They have tried everything from pulling them out by hand to cultivating to spraying to the direct application of fire.

Always looking for ways to reduce weed pressure, seed companies genetically engineered products to be resistant to glyphosate herbicide which Monsanto markets as Roundup. When approved for general use in 1994, a few scientists were concerned that overuse of the popular weed killer could lead to plants becoming resistant to the herbicide.

But it appears it was only matter of time.  The first weeds resistant to the herbicide Roundup were discovered in 1996. Since then, 24 states have reported the problem with the greatest difficulty being seen in those producing cotton. And, while not as prevalent, some Midwestern farmers also are finding Roundup resistant weeds in their corn and soybean fields.

Mark Jeschke, Agronomy Research Manager, Pioneer Hi-Bred:  “think of it kind of like baseball, you can't go out there and throw the same pitch every time and expect to win.  Weeds are very adaptable. If you throw the same thing at them over and over they will eventually overcome it.” 

Over the past 15 years, scientists have identified more than 20 plants with resistance to glyphosate herbicides including Palmer amaranth – more commonly known as pigweed--, water hemp, giant ragweed, kochia (koshia) and mare’s tail.

Larry Steckel, a University of Tennesse –Jackson Extension Weed Specialist, believes the days of weed control being handled by making a few spray passes over emerging herbicide tolerant plants are gone.

Larry Steckel, University of Tennessee –Jackson Extension Weed Specialist: "I tell our growers in a lot of meetings…- you can always think back on 2003 as being the good ole days when it comes to weed control because it is never going to be that simple or easy again.” 

Steckel believes growers need to go back to weed control methods used prior to 2003. And he’s calling for a resurgence of both hand and machine cultivation, an increase in crop rotation, the planting of cover crops and the use of herbicides previously set aside for the advantages of glyphosate.

 Larry Steckel, University of Tennessee –Jackson Extension Weed Specialist: “Now everybody moved into the Roundup technology in the mid-90s and that didn't happen in a vacuum.  A lot of these farmers got very big.  They farmed a lot more acres than they did in the 80s. And you can do that when Roundup controls weeds at any size with one of these big sprayers, you know, and we - once you have to go back to these herbicides and rely almost exclusively on those that we were using back in the 80s we just don't have as many sprayers, as much labor, and as much time as we need to get things sprayed as timely as back when we were using the same herbicides in the 80s.”

Pioneer Hi-Bred, a national underwriter of Market to Market, and Monsanto, a biotechnology giant in its own right, are two of the top purveyors of Roundup Ready products in the United States. Representatives from both companies recommend essentially the same protocols for problem weeds. They tell farmers to be diligent when scouting fields, be prepared to use multiple modes of action to eliminate the problem and always apply herbicides as directed on the product’s label

Additionally, Pioneer officials recommend consulting with their seed sales professionals and agronomists as well as taking advantage of Pioneer’s online library for assistance.

Mark Jeschke, Agronomy Research Manager, Pioneer Hi-Bred: …Preventing the spread of seeds from resistance plants is very important too.  Tillage equipment and combines especially are exceptionally capable of taking weed seed from one field and spreading it in another so that might mean harvesting a field with resistant weeds last or possibly cleaning machinery before moving between the fields, which I know nobody wants to spend the time doing that, but if it means preventing a resistance problem it could be a worthwhile investment."

Monsanto offers similar services and has added a monetary rebate program that encourages farmers to use a broader spectrum of chemicals to combat weeds. The incentives range from $10 per acre for soybeans to $22 per acre for cotton.

Rick Cole, Technology Development Manager, Monsanto: "…Now it is multiple modes of action, it is using two or three herbicides that have overlapping effects on the weeds so that you don't get into a situation where you only have one herbicide and you're starting to select for the resistance.  Resistance is always out there.  You just have to make sure you don't select for it by using multiple modes of action."

What we do as part of our Roundup Ready Plus platform is go to academics, go to third parties, ask them what the best recommendations are, what products would they use for these key weeds and then we put them into our program and we make the recommendation.”

The program is unique in the marketplace and offers rebates on a myriad of chemicals made by a laundry list of manufacturers.

Both Pioneer and Monsanto recommend the use of residual herbicides that are applied pre-seed or preemergent. Depending on the crop, products containing dicamba, atrazine and 2, 4-D are being recommended to handle glyphosate resistant weeds.

Implement manufacturers also are adapting their products. Willmar, Minnesota-based Willmar Fabrication, for example, makes a spray hood designed to decrease herbicide drift and increase direct application to problem weeds.

And waiting in the wings are the next lines of herbicide tolerant crops with resistance to chemicals already in the farmers weed arsenal. Despite the encouraging news, these new seeds are still a few years away from commercialization.

For now, farmers will need to be diligent about watching and waiting to see if herbicide-resistant weeds creep into their fields.

For Market to Market, I’m David Miller. 

Tags: agriculture big ragweed mares tail Monsanto pigweed Pioneer Hi-Bred Roundup Roundup Ready Plus water hemp