Discipline and a pro-active attitude are requirements if farmers hope to slow the spread of herbicide-resistant weeds on Alabama cropland. That’s the message being carried by Auburn’s team of researchers and Extension specialists who are traveling to communities throughout the state in an effort to help producers battle a problem that is becoming increasingly severe.
Farmers in Alabama will generally will have to deal with four different weed species that have become resistant to glyphosate, or more commonly known as Roundup. Palmer amaranth or pigweed, and horseweed, also called mare’s tail, are popping up in crop rows as usual but are now holding a firm fight against glyphosate – a product that controlled them well for so many years.
More recently, common ragweed and goosegrass populations have been found with suspicious resistance to glyphosate, adding two more problematic weeds to the list.
Auburn University weed scientists and extension specialists, like Scott McElroy of the Department of Crops, Soils and Environmental Sciences, are taking this problem head-on.
“We’ve learned a lot about the development of herbicide-resistant weeds and especially about how management practices influence development,” McElroy said. “One of the specific things the public needs to understand about this problem is that it is a natural selection problem that was brought on by the continuous use of Roundup.”
Farmers, researchers and turfgrass managers all became too reliant on Roundup, McElroy believes.
During Roundup’s heyday, the weeds that survived the herbicide the longest produced the most seeds. After this process repeated itself for multiple growing seasons, the strongest weeds weeded-out the weaker weeds.
A pigweed plant can grow to be more than 6 feet tall and carry more than 1 million seeds. With each plant carrying that many herb-resistant seeds, it’s easy to see how the severity of the problem has grown so rapidly.
Glyphosate-resistant weeds are not just an Alabama problem. Twenty-two states, largely in the South and Midwest regions, have reported cases of glyphosate-resistant weeds.
Researchers found that most glyphosate-resistant weed cases began in southern Georgia and Arkansas. Birds and wind spread most weed seeds, but Alabama’s forests and high elevation in the north don’t make for the best traveling for seeds. One missing piece that provided an answer was used farm equipment, with glyphosate-resistant weeds being brought in tractors and combines from invested states.
Weed Scientist for the USDA’s National Soil Dynamics lab in Auburn Dr. Andrew Price said herbicide-resistant weeds pose one of the most significant threats to soil conservation since the inception of the USDA NRCS.
“We have a situation where farmers need to maintain a standard of crop yield, but herbicides aren’t as affective as before,” Price said. “If the only way you can kill the plant is by physically pulling it out of the ground or burying it, then farmers will adopt more conventional tillage into their rows instead of conservation tillage.”
Conventional tillage, in its simplest form, kills weeds by a combination of severing shoots from roots, uprooting, or burying and covering the plant underneath the surface.
The disadvantages that come with conventional tillage include more soil erosion, loss of soil moisture and structure, and higher expenses with equipment, operations and energy.
“If and until we do find a better solution to herbicide-resistant weeds, farmers will need to implement more diversity into their farming, which takes a lot of discipline,” Price said. “We all failed, in a way, to preach more diversity in herbicides for crops and now we need to move forward with diversity in every aspect of farming.”
Variance, in farming methods and tillage, is the only surefire way to at least slow down the spread of glyphosate-resistant weeds according to Price.
Looking forward, more research is needed to determine the best ways to manage glyphosate-resistant weeds while at the same time meeting soil conservation compliance goals and producing a profitable crop yield.
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