What is in this article?:
- Managing the mounting pain of pigweed
- Pre-emerge herbicide necessary
- Arkansas weed scientist Ken Smith is recommending that growers include as many weed control options as they have at their disposal – cultural, mechanical and chemical – to keep the pain of glyphosate-resistant pigweed manageable.
- Smith spoke to farmers attending the PigPosium, in Forrest City, Ark., sponsored by the Arkansas Cooperative Extension Service and Farm Press.
- The symposium, attended by close to 800 people, focused on the impact of glyphosate-resistant pigweed.
Glyphosate-resistant Palmer pigweed is like a pain that starts up in your back when you turn 40. If you keep doing things the way you’ve always done them, it will likely get worse.
That’s why Arkansas weed scientist Ken Smith is recommending that growers include as many weed control options as they have at their disposal — cultural, mechanical and chemical — to keep the pain of pigweed manageable.
Smith spoke to farmers attending the PigPosium, in Forrest City, Ark., sponsored by the Arkansas Cooperative Extension Service and Farm Press. The symposium, attended by close to 800 people, focused on the impact of glyphosate-resistant pigweed.
Glyphosate-resistant pigweed “is not going away,” Smith said. “There is not going to be a silver bullet next week. We need to think about what we need to do to manage this pest. It is here to stay.”
Smith said none of the weed control tools available for farmers is without weakness. For example, while rotating from cotton to corn can allow a farmer to rotate chemistries for more effective control of pigweed, real life experience may reveal otherwise. “A farmer told me that as he was combining his corn, he was running into pockets of pigweed, and knew he was spreading them. But he never saw them until he ran up on them. They were sneaking up on him. He could see them in cotton and soybeans, but not in corn.”
Cultivation is also a consideration, according to Smith. “We had long forgotten about tillage. We don’t want to do go there, and I’m with you. But it is a consideration. For many farmers, it’s their last consideration.”
Hand hoeing is another option for growers, especially when there are isolated patches of resistant weeds. “I’ve heard costs of $3 to $100 an acre for hand hoeing,” Smith said. “Three dollars an acre is cheaper than any herbicide we put on. It’s an option and a tool we need to keep in our program.”
Chemicals can also bring fields back under control, but will add cost, and will require a proactive, deliberate approach, which could be a challenge for producers, Smith says. “We are accustomed to farming in a hurry. We need to slow down and take our time. We can’t ignore pigweed. It won’t go away.”
Smith said the huge turnout at the PigPosium is a good sign “that many producers are past the stage of denial.”
While pigweed is an ideal weed because of its high seed production and rapid growth habit, it also has a weakness, seed longevity. “It doesn’t last very long, up to six years,” Smith said. “Our data in the Delta says seed mortality is 99.9 percent after four years.”
The weakness of the seed “gives us an up on managing the soil seed bank,” Smith said. “We have a program called zero tolerance, where we do not allow a seed to be produced. We walk the field on a regular basis to chop the weeds out and make sure we don’t have seed production. We’re going to repeat this again next year on our zero tolerance fields. Hopefully, the trips across the field are going to be reduced significantly.”
Smith says the soil seed bank, or the number of pigweed seed in the germination layer, “must be stable or decreasing is order to be sustainable. This is not rocket science. This is arithmetic. If we do not decrease our soil seed bank, we cannot fight this weed. Ninety-nine percent control may not be good enough, depending on how many you started out with. If you have one per square foot, you might. But if you have a hundred per square foot, 99 percent control still leaves you one per square foot.
“The moral of the story is to not let the seed germinate. Unlike in soybean production, we do not have the option to come over the top. We must rely on pre-emerge and overlapping residual herbicides.”
Here are some of Smith’s suggestions for chemical control: