No question – Roundup was a revolutionary herbicide that changed weed control. Also no question – overuse of Roundup has created glyphosate-resistant weeds that are now pretty much everywhere that row crops are grown. Here is the question: Why do growers continue practices that lead to herbicide resistance?
Weed resistance was identified in the northwest Piedmont foothills in North Carolina just three to four years ago. Tim Hambrick, North Carolina State University Extension and a Syngenta Resistance Fighter of the Year, said he has two groups of farmers – those who are proactively looking ahead and those who are content to continue with the way they’ve been doing it for years.
Tim Hambrick, North Carolina State University Extension and Syngenta Resistance Fighter of the Year
"My proactive growers, who account for about half of our soybean acres, are always looking to the future. They have paid attention to the resistance they were hearing about in neighboring states and took action by adding another mode of action to their tank," said Hambrick. "It may have been something simple and cheap, but at least they were preparing. In the last two to three years, this group has also started looking much harder at pre-emergence herbicides that have multiple modes of action."
Hambrick’s content growers still depend on a Roundup burndown and a Roundup post-emergence spray. When an infestation occurs, it’ll be two to three years before they actually go ask somebody "why is this not dying anymore?" They tell themselves it’s just a miss or a wrong rate. But weed resistance is dangerous, and by the time they ask for help, they usually have a huge problem in their field that will be expensive and time-consuming to fix.
"You’ve got to have a certain amount of fear to attack resistant weeds. I had to see up close and personal the damage that Palmer amaranth can do. I can still remember driving up to a demonstration field and thinking it was a field of nothing but head-high Palmer amaranth, but there was a soybean crop planted," he said. "That was a turning point for me in understanding the damage resistant weeds can cause and the time and effort needed to fix those fields over several years."
Many content growers believe that until weed resistance is at their doorstep, it’s not their problem and won’t happen in their fields. He uses a similar field day demonstration to show growers the production and economic devastation resistance can cause. With the build-up of weed resistance, he said it’s not just seen in field plots; growers can see resistant infestations every day in local fields.
"I tell all of my growers – use herbicide full rates, walk your fields and know what weeds you have. With Roundup, it killed absolutely everything. But times have changed and now you need to know which weeds are not dying and understand the biology of those weeds," Hambrick said. "Resistant weeds become the driver for the whole weed management system, changing decisions on modes of action, application timing and many things during the process."
A Grower’s Perspective
Trey Koger, a corn, soybean, cotton, rice and peanut grower from Belzoni, Mississippi, said the soil type for their 12,000 acres of farmland is very diverse and has a huge impact on the crops they grow. Crop acreage and management practice decisions are based primarily on commodity markets, input prices, crop rotation and machinery availability.
From a historic perspective, Koger said the Delta in Arkansas, Louisiana and Mississippi was planted virtually wall-to-wall with cotton. When Roundup Ready cotton came out, it revolutionized weed control in the South.
"We used to spray five or six times with herbicides containing multiple modes of action to try to keep a crop clean until we defoliated," Koger said. "When we switched to Roundup Ready Flex cotton, it changed everything. It made farming cotton so much easier. Now we have a younger generation of farmers, including myself, that has never experienced the days of cultivation and multiple modes of action. It has been a huge learning curve for all of us learning how to farm in a weed-resistant environment."
Koger said on his farm, an extremely wet spring and a late-planted soybean and cotton crop allowed pigweed to get a foothold in his fields. He said because of the weather, they didn’t do a good job making sure they were clean at planting or crop emergence. The result – pigweed is everywhere. For the next several years, he knows he’ll be battling pigweed.
"It’s a numbers game with pigweed and right now the pigweed is winning," he said. "But what I do know is we’re going to farm the land. Weed resistance is not going to derail our farm or farming in general. Across the farming landscape, are we going to have fields with losses and disasters? Yes, that’s going to happen, but we’re going to figure out a way to manage weeds. Eventually, we will figure out a way to grow a clean crop."
New technologies factor into his optimism. Some of the new technologies on the horizon may have some baggage and limitations, but he believes that along with cultural best management practices, they can play a role in managing weeds.
"Personally, I am looking forward to new technologies being part of our weed control systems and plan on using them as soon as they are registered and available to plant," he said.
Cost is a significant decision driver for many growers. There’s no doubt the cost of weed management has gone up since the glory days of a Roundup program.
"Two applications of glyphosate cost growers about $20 per acre," said Stevan Knezevic, professor at the University of Nebraska-Lincoln. "Programs that will actually slow the weed resistance process will cost more. The next question is how much more, and the grower mindset often is ‘maybe I can get by one more year [without it]’."
In Nebraska, Knezevic estimates that about 50 percent of growers are still using Roundup as their foundation program. About 25 percent are beginning to have problems, and they are using soil-applied chemistries or diversifying programs with different sites of action. Another 25 percent have serious weed resistance problems, and they’re spending a lot of money trying to fix the problem.
"There’s definitely a ‘I never thought it would hit my farm’ mentality," he said.
New technologies are important, but expectations should be tempered, Knezevic said. Company promotions tend to encourage growers to think, "I’ll just go one or two more years the way I have been and hopefully no major resistant weeds will hit me, but if it does hit, we’ll fix it with the new technology that’s being talked about."
If It Works, Change It
If a grower’s program is working well, it’s time to change. It’s not necessarily a popular concept with growers, but it’s an important one.
"Diversity is really key in trying to maintain the sustainability of the herbicides we have available, so they remain effective for the future," said Don Porter, Syngenta herbicide technical lead. "We must be good stewards of the chemistry and learn from our experiences over the last 20+ years."
Renowned weed resistance expert Stephen Powles, Ph.D. with the University of Australia came to the U.S. in 2005, and at that time, glyphosate was working well in the U.S.
"Dr. Powles’s message to growers in 2005 [and in the years since] was diversity, diversity, diversity. If something’s working today, then change it," Porter said. "The weeds always figure out how to survive. The herbicides that are effective today will no longer be effective in the future. So if you don’t change your practices, then you will run out of the chemistries."