For southern growers still debating the economic value of a fall burndown herbicide treatment, consider this: you’re not just controlling winter annual weeds, you’re also eliminating a key food source for overwintering bugs.
“It’s not really a weed issue, it’s an insect issue,” says Daniel Stephenson, a weed scientist with the Louisiana State University (LSU) Ag Center. “If you kill the weeds early enough, the insects don’t have anything to eat, so they move on.”
They call it, “breaking the green bridge,” meaning you eliminate vegetation that hosts pests between crops.
“If you can control your winter annual weeds with a fall burndown, that will break the pest life cycle above and below the ground,” explains Sebe Brown, an entomologist who is also with the LSU AgCenter. “We have issues with insects that move off weeds into the crops, so it’s really beneficial to our growers if they can disrupt that next generation.”
Both henbit and Italian ryegrass are key weeds that harbor economically damaging insects, and fall burndown applications are the most effective approach to controlling them, he adds.
“Henbit is a very hardy plant that harbors twospotted spider mite,” explains Brown. “If you leave the henbit in the field and then plant into it, the twospotted spider mites will crawl into your crop. That means spending more money – and earlier in the season than normal – to control spider mites. In addition, Italian ryegrass hosts cutworms, three-cornered alfalfa hoppers and below-ground insects like southern corn rootworm.”
From a pest-control standpoint, fall burndown treatments make economic sense, says Stephenson.
“If you have large henbit or Italian ryegrass in the spring, it’s extremely expensive to terminate that weed so that it won’t cause problems with the farmer’s summer cash crop,” says Stephenson. “It’s much more economical to control these weeds when they’re emerging.
“Henbit emerges in the window from Halloween to Thanksgiving and Italian ryegrass just a bit earlier. If you take out the emerging flush in the fall then your life is a lot easier the next spring.”
The fall burndown also adds efficiency to a weed management program. Spring herbicide treatments for weeds like henbit just aren’t as effective, according to Stephenson. “Our growers always have difficulties controlling henbit with a spring burndown application,” he says. “That’s because it’s large by March. Plus, the plant is beginning to naturally senesce so there’s not as much leaf area to intercept the herbicide and allow it to work efficiently to kill the plant.
“If you treat in the fall, though, you may not have to do anything in the spring. Or, you may be able to do a much cheaper herbicide program in the spring and avoid expensive sequential herbicide applications,” he says. “Starting with a fall burndown is a lot cheaper and it gives you a much broader window in the spring. You want to start as clean as possible.”
Skipping a fall burndown herbicide treatment can be a real gamble for growers, says Brown.
“Think about spring weather – if it’s wet and cold, you may not get spring herbicide treatments out in a timely manner,” he notes. “But if you’ve done that fall application, you have less weed cover on the ground, your soil will dry out faster and you can get in and plant without having to take out a big carpet of weeds or deal with the insects that come with them.”
- For more information about breaking the green bridge, click here.
- To learn how to properly identify henbit versus other closely-related weeds, check out this guide from the University of Tennessee Extension.