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Weeds To Watch 2016: An Ever Growing Problem


As the 2016 growing season gets into full tilt, there’s one undeniable fact ag retailers and their grower-customers are quickly facing up to — the problem of herbicide-resistant weeds continues to grow, both literally and figuratively. According to the International Sur­vey of Herbicide Resistant Weeds, 238 types worldwide show resistance to one or more active ingredients (A.I.s) and have resistance to 22 of the 25 herbicide sites of action within plants. All told, weeds show resistance to some 155 herbicides worldwide.

Closer to home, most industry experts believe that approximately 45% of all the farm acres across the U.S. contain weeds that have shown resistance to glyphosate-based herbicides as of the end of 2015. And if you add in weed types that have resistance to other forms of active ingredients (A.I.s), this percentage climbs even further.

“Based upon our own research, we believe that more than 65% of U.S. crop growers have some form of resistant weeds present in their crop fields,” says Pablo Ogallar, U.S. Soybean Products Manager for Bayer CropScience. “This has become a very serious problem that is facing growers to have to change their mindset on how to deal with weed pressures.”

For example, research indicates that one common herbicide-resistant weed — giant ragweed — is evolving somewhat to keep ahead of not only herbicides such as glyphosate and ALS-inhibitors but basic farming practices as well. Possessing seeds that are larger than most other weed species, giant ragweed can emerge from deep within the soil, meaning that regular tillage methods may actually help it germinate. In addition, the weed has traditionally emerged early during the summer season but has now extended this emergence pattern into July. “Giant ragweed has adapted well to the common practice of no-till soybeans followed by some tillage ahead of corn,” says Mark Loux, a weed scientist at The Ohio State University.

Then there’s Palmer amaranth. A cousin of tall waterhemp, this herbicide-resistant weed type has been systematically extending its territory north and westward for several years now. In fact, according to the data, 25 states have confirmed populations of glyphosate-resistant Palmer amaranth. And the weed’s impact on yield is staggering, with losses of upwards to 80% in soybean fields with severe infestations.

“Our research shows that there are no genetic or environmental factors to keep Palmer amaranth from competing with crops and reducing yields in Northern geographies,” says Adam Davis, a weed ecologist with the University of Illinois. “It can complete its life cycle in a very short period of time. Even if you killed early-season populations, if it comes up again in late summer, it can still produce seed by harvest time.”

New Developments In 2015-16

Besides these well-known and already established herbicide-resistant weeds, new ones are being discovered all the time. Consider these select findings over the past 12 months alone:

In April 2015, researchers in Australia confirmed the presence of a form of sowthistle weed in the southern part of the continent that showed resistance to 2,4-D.

In October 2015, researchers at Texas A&M University discovered a variety of yellow nutsedge that had developed resistance to ALS inhibitors. In addition, this biotype also showed delayed emergence and high levels of dormant tubers.

In January, researchers announced the finding of an annual sedge in Georgia that was resistant to ALS-inhibitors.

“We think that weed resistance increases in the number of species is only as striking as the number of new geographies now dealing with them,” says Dr. John Pawlak, Product Development Manager for Valent U.S.A. Corp., which is promoting its Fierce XLT soybean herbicide in 2016. “Based upon our research, these are being moved around primarily by birds and the shipping of popular commodities across the country, such as alfalfa being used for cattle feed.”

Added to these regular resistant weed seeds spreaders were factors more unique to 2015. “Last year was very wet and rainy across much of the Midwest throughout the spring,” says Dave Johnson, Product Development Manager for Soybean Herbicides for DuPont Crop Protection. “We think that some of this excess water and possible flooding of fields could have moved around a lot of weed seeds, many of which will begin to emerge in new places during the 2016 season.”

According to its own company research, herbicide-resistant weeds remain a top concern of the nation’s corn and soybean growers. In fact, according to a survey of 1,200 growers conducted by DuPont in 2015, 85% said they worry about controlling resistant weeds on their farms, with most using crop rotation and/or tank-mix herbicides with multiple modes of action to address the problem.

“Palmer amaranth has become a particular problem weed in our fields,” says Alan Gohn, a corn and soybean grower from Rochester, IN. “We are using multiple modes of action herbicides to try to control it, but that has raised our production costs significantly over the past few years. If I had to guess, I would say that these have doubled on a per acre basis during that time.”

Because of this need for more modes of action chemistries, the popular trend the past few seasons has been to introduce herbicides that features multiple A.I.s in their formulations. Some recent examples of this would include Canopy Blend from DuPont, a burndown and residual control herbicide featuring two modes of action, and Armezon PRO from BASF, which is a combination of topramezone and dimenthenamid-P.

Even More Products

An even more extreme example of a blended product is Acuron from Syngenta Crop Protection. A mix of four A.I.s and three modes of action, Acuron has served as a successful control for such tough weeds as giant ragweed and morningglory, says John Foresman, Herbicide Brand Manager for Syngenta, in the more than 800 field trials conducted over the past few years. And in 2016, the company is introducing a new version called Acuron Flexi which contains one less A.I.

“This version doesn’t contain atrazine, which isn’t used on approximately 40% of the acres out there,” says Foresman. “So Acuron Flexi can be used by growers in parts of the country such as Wisconsin and Northern Iowa, where that active isn’t allowed, or where high pH soil types are present and atrazine could affect soybean rotation.”

Another new example of three A.I.s coming into the market in 2016 is Resicore from Dow AgroSciences. A blend of acetochlor, mesotrione, and clopyralid, Resicore is designed to provide non-glyphosate and non-atrazine modes of action to growers to combat such hard-to-control weeds as waterhemp, giant ragweed, and marestail.

“Resicore is different from other premixes on the market particularly because it has three active ingredients growers have never seen together before in a single product,” says Luke Peters, Corn Herbicides Product Manager for Dow. “The novel formulation has the right balance of active ingredients to offer superior weed control deep into the growing season.”

Another approach to handle resistant weeds comes from FMC Corp. This year, the company has introduced a stronger concentration of its Anthem herbicide for corn and soybean growers. Called Anthem Maxx, this product features usage rates of 2 to 6.5 ounces per acre on corn and 2 to 5.7 ounces per acre on soybeans — approximately half the rates for Anthem when the product was launched in 2013. “Anthem Maxx herbicide has the same benefits that growers are familiar with getting from our Anthem herbicides with a decreased use rate, cutting the rate in half,” says Matt Hancock, North America Corn Segment Manager for FMC Agricultural Solutions.

Also coming in 2016 are Roundup Ready 2 Xtend soybeans from Monsanto Co. Engineered to be resistant to both glyphosate and dicamba, Roundup Ready 2 Xtend products should aid growers in their fight against tough weeds, says the company.

“I’ll definitely plant Roundup Ready 2 Xtend Soybeans next season,” said Joe Neuser, a grower from Mishicot, WI, at the Monsanto Commodity Classic booth. “It will be great to have another way to control some of these weeds.”

Future Developments

Besides the dicamba and 2,4-D-resistant cropping systems already entering the marketplace, others are reportedly in the works. For instance, researchers are working on crops that will be resistant to HPPD inhibitors such as mesotrione and isoxaflutole. And in 2017, Dow is hopeful of introducing a new burndown herbicide called Elevore that will feature a new A.I. and Arylex active. “This will be a Group 4 mode of action product to inhibit growth and it should be effective against such stubborn weeds as chickweed and marestail,” says Lindsey Hecht, Product Manager, U.S. Soybean Herbicides for the company.

According to Syngenta’s Foresman, all these tools — and many more — will likely be needed by U.S. growers to keep ahead of the growing herbicide-resistant weed problem. “Right now, the research suggests that almost half the farm acres in this country have some form of glyphosate-resistant weeds in them,” he says. “But by 2025, this number is expected to have increased to more than 75%. Given this, I would say the greatest crop production management challenge facing growers today and for many years to come is getting a better handle on their weed control. Hopefully, this is a challenge we in the crop protection industry will be able to help with.”

Source: Eric Sfiligoj, CropLife

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