May 28, 2009 - When Texas AgriLife Extension Weed Specialist Paul Baumman worked at the Bayer Headquarters in Germany, 10 years ago, he was surprised to find a researcher at the company spending a lot of research time and money developing herbicide chemistries
“Not many companies were doing that then because Roundup was already out there, but as a biologist, he saw Roundup resistance coming,” Baumann said.
He added that the Roundup is still a good tool, but that resistance to the herbicide is showing up. Water hemp along the Gulf Coast has already developed Roundup resistance, and Baumann said there is no reason to think it won’t spread to other parts of the state.
“We have to start employing practices now, like combining Roundup with a pre-emergent herbicide,” he said.
Baumann made his comments to producers attending a corn herbicide and drift management clinic at the Jefferson Davis Farm near Speegleville, earlier this month. Davis donates part of his farm to test plots, where various herbicides are tested on corn. Baumann pointed out one plot that was essentially clean except for some Johnson grass that had recently sprouted.
“When you get grasses this late, it won’t affect the yield but it will form a seed head and it will come back even stronger next year,” he said.
“You can’t let a small problem go. If your herbicide misses the weed now and that weed puts out 200,000 seed heads, you’re going to have problems. You can come back with an alternate treatment, but once that weed is out of the box you’re sunk.”
Certain grasses, like Johnson grass, put out rhizomes, which send out roots and stems from which new grass sprouts. A post-emergent herbicide will take care of the rhizomes, Baumann said.
Current strategies for battling Roundup resistance involves planting one crop variety with the Roundup-resistant gene and one with an Ignite-resistant gene.
“If that weed is resistant to one herbicide, the other one will come along and pick it up,” he said. “It’s rare to see a weed that’s resistant to both.”
Baumann said it’s not enough to make a plant sick; it has to be killed.
“With water hemp, say you’re late applying your herbicide and you come along later and see it’s yellow but not dead; you don’t want to leave it alone so it can get healthy again,” he said. “You have to hit it with that follow-up application while it’s still sick.”
When to apply that follow-up application sometimes depends on weather conditions, which can affect weeds as well as crops. If the weed is weakened but not dead from herbicide rather than natural conditions, Baumann suggests applying that follow-up application.
Baumann said that while herbicide technology has come a long way in the last 35 years, producers have a lot fewer companies that manufacture herbicides to choose from.
“There used to be 25 or 35 companies making herbicides,” he said. “Now it’s down to four or five.”
