What is in this article?:
• One of the hindrances to resistance management is economics.
• Acreage has expanded and people don’t cultivate anymore, so to go backwards is a hard pill to swallow.
• There’s also denial about having or ever getting the problem.
Some deny the problem
There’s also denial about having or ever getting the problem, says Prostko. “There’s also a belief out there that there’s a new herbicide on the horizon, but there’s not, at least not a new mode of action that will give us some relief from the load that we’re putting on current herbicides.”
In Georgia, he says, resistance management is taking several forms. “We hear a lot about crop rotation, and we know when you rotate crops you can do other things. If you look at the data, cotton is the least competitive crop with Palmer amaranth. Going to a crop that is more competitive is one reason for going with a rotation, along with some of the other benefits you receive.”
Tillage and cultivation also are receiving more interest, he says, maybe not plowing every year but at least once every three or four years.
“We’re also doing some extreme cover crops. This is where a grower will plant a rye cover crop in the fall and manage it to get to the maximum height and then terminate it in the spring with herbicides and rolling, and then strip-till into it. That cover crop has a suppressing effect on Palmer amaranth, but that’s not something everyone can do.”
Row spacing is another factor, says Prostko. “While we don’t grow a lot of soybeans in Georgia, we still grow a few, and we plant some of those in wide rows. Palmer amaranth doesn’t like shade, so we know if we go to a narrower row, we can pick up some benefits.”
Everyone knows by now, he says, that we can’t rely strictly on herbicides. Other things must be done in the battle against resistant Palmer amaranth pigweed.
“One of my responses to what can we do about Palmer amaranth is to dig a well,” says Prostko. “We need residual herbicides, and the only way we can get them to work is with water. In Georgia, about 50 percent of our cotton and 50 percent of our peanuts are irrigated. We should be able to do a better job.”
Modes of action can be a scary term because it has to do with chemistry, he says, and no one likes chemistry, but you don’t have to be a scientist to understand what it means.
“Some herbicide labels will have it clearly on the label. The University of Georgia has put together a master list of herbicides with their common name, trade name and mode of action, as well as putting the modes of action in our recommendations.
“We also want to encourage growers to put together a long-term resistance plan or mode of action plan. This is where we write down the rotation or the sequence and fill in the blanks with the herbicides you’ll use. When you come to the end of the column, you can figure out how many modes of action you have, and you can see where you’re making two or three applications of the same mode of action.”
Other things to be considered are tank-mixtures or pre-mixtures, says Prostko. “For these mixtures to be most effective in delaying the evolution of resistance, ideally they must have different sites of action, they should have similar efficacy and persistence but also different propensities for selecting for resistance or different modes of action.”