By Alan Goforth
Producers who are sold on less tillage are beginning to tangle with resistance issues
Variety is said to be the spice of life, and it also might be the key to herbicide resistance management in no-till fields.
The agronomic and economic benefits of no-till production have been well documented. Despite having fewer herbicide and cultural options than in conventional tillage, no-till producers have been able to maintain an acceptable level of weed control.
However, a recent increase in the number of confirmed herbicide resistance cases is raising concern among farmers and others.
"Resistance is a concern anywhere you are using glyphosate," says Mark Watson, a farmer and education coordinator for the Nebraska Panhandle No-till Partnership. "I haven’t seen
resistance on my farm, but I am concerned about people who are planting both Roundup Ready corn and sugar beets."
Blake Hurst of Westboro, Mo., and his family have been growing no-till corn and soybeans for at least 20 years. They are also keeping an eye on the potential for resistance.
"The biggest challenge is resistant pigweed, and resistant waterhemp likely is coming our way," Hurst says. "My brother farms 20 acres at our local airport, which is continuous soybeans because the FAA [Federal Aviation Administration] won’t let him plant corn. He is noticing that waterhemp is becoming harder to control."
Some no-till producers are reluctantly adding various levels of cultivation to battle resistant weeds. Watson and Hurst believe they can keep any problems below a low economic threshold through diversity, both in their crop rotation programs and in their choice of herbicides.
Break the cycle. The strategy behind crop rotation is to break the cycle of glyphosate-resistant crops.
"In our area, we have a fairly broad crop-rotation program," Watson says. "Where we can get into trouble is with multiple glyphosate applications in the same season. On our farm, we rotate wheat with corn and field peas. We use Roundup Ready just a few times over the course of three years."
By contrast, northwestern Missouri is pretty much corn and soybean country. "Adding a different rotation crop such as wheat is a good practice," Hurst says. "But we don’t use it in our rotation because our growing season is too short to double-crop.
"Some of the most effective herbicides need to be incorporated, so we can’t use them," he says. "We are still planting Roundup Ready soybeans, but we plant LibertyLink corn or use conventional herbicides. The best advice is to rotate your chemistry."
Hurst intends to follow this approach unless he runs into problems with resistant weeds that can’t be managed except with tillage. No-till fields never have the same level of weed control as conventional fields, but he feels the practice makes up for it in lower production costs and healthier soils.
"In some years we see a yield drag from weeds, but in other years, such as those that are wet, no-till saves us time and lets us get in the field a week earlier," he says.
Know your options. Keep in mind that no-till doesn’t have to mean no cultural options. Practices such as row-width selection and residue manage-ment can also help control weeds.
"A reliance on technology to keep your fields weed-free places too much pressure on these technologies and sets you up for problems down the road, such as herbicide-resistant weed populations," Watson says.
"Remember to use cultural practices as a front-line defense against weed populations, and use herbicides to help control the weeds that persist despite good management," he says.