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Invasive cogongrass’ marchInvasive cogongrass’ march

David Bennett

June 11, 2007

6 Min Read

Known as one of the 10 worst weeds in the world, cogongrass came into the United States through an Alabama port around 1911 as packing material.

The weed’s ability to take over the landscape was recognized too late. In fact, through the 1930s and 1940s, some farmers planted cogongrass in a bid to make it a forage crop for cattle. Others tried it as a soil stabilizer. It performed poorly at both.

“Cattle will eat cogongrass when the plant is young,” says Rick Williams, Extension Forestry Specialist, West Florida Research and Education Center, University of Florida. “But as it matures, the plant has silica on the edges and will cut cows’ mouths. They won’t feed on it unless there’s nothing else.”

Even though the plant was no longer planted and encouraged, cogongrass kept spreading. Estimates are that between 500,000 acres and 1 million acres are infested with cogongrass in Florida, Alabama, and Mississippi alone. It’s also found in pockets from South Carolina to Texas.

“It’s already widespread and is always on the move,” says Williams, now stationed in the Florida panhandle. “We do a lot of the spreading unknowingly because of dirt being moved that contains roots. That happens commonly in road work or field work.”

Cogongrass spreads primarily from rhizomes and rhizome fragments. Even a small rhizome fragment “can develop into a fully functional plant. Cogongrass is highly flammable when mature and actually burns hotter than native grasses, but the roots and rhizomes are remarkably resistant to fire.”

Williams has seen cases where landowners had dirt dumped to fill a hole and ended up with a cogongrass patch.

“It also spreads by seed. Cogongrass produces a lot of seeds, but they aren’t viable for a long time.”

As with other invasive species, the big problem with cogongrass is its speed of growth and habit of crowding out native plants.

“Look at kudzu. Often, invasives just take over. They can affect the landscape, environmental balance, agriculture, trees.”

Invasives also affect wildlife dependent on the native plants. That means food supplies dwindle and affected species falter.

This is not a minor concern. “The U.S. Fish and Wildlife Service estimates that 42 percent of endangered species are in decline because of invasive plants. That’s a huge impact.”

Able to reach a height of 5 feet, cogongrass is “an aggressive, colony-forming perennial grass. These plants must be controlled and a lot of research work has been done on cogongrass. The basic recommendations include using an imazapyr, like Arsenal. And those are certainly effective, although expensive.”

Glyphosate has been used, but it often requires a series of re-treatments. Although less frequent, Williams says, re-treating with imazapyr is sometimes required.

“The problem with cogongrass is most of the material is underground. It’s very difficult to get chemical to it.”

Williams is also concerned with people who actually use cogongrass for landscaping. Akin to inviting a tiger to the playground, if the plant gets away it can ruin a landowner’s investment.

“It’s almost impossible to get rid of. So much of the plant is underground, it’s amazing. Some studies show there can be up to 17 tons per acre of below-ground root mass from this plant. The other roots can’t compete. The cogongrass intertwines with them and chokes the other plants down.”

There’s also a barb on cogongrass roots. If pressed, it will actually dig itself through the roots of trees.

“It’s like driving a spike. Dig some cogongrass roots up and you can feel those spikes.”

Several years ago, Williams began studying how best to tackle cogongrass. One thing he looked at was product enhancers.

“Cogon-X is one we tried in a mix with glyphosate. That mix gave us good results and took the cogongrass to a workable level. A few sprigs may survive, but the mix knocks it back significantly.”

Williams believes that battling the invasive weed will be an ongoing process. But, so far, we’re seeing good results with glyphosate and Cogon-X. The same is true for the imazapyr products.”

Imazapyr products — Chopper, Arsenal — do the best on cogongrass. The plant “takes them up” with the most enthusiasm. But landowners and farmers aren’t happy with the products’ cost.

Rather than shoulder the cost of an imazapyr treatment, landowners often leave the problem for another day. That can mean the cogongrass is just left to take over.

“That’s the worst thing that can happen. I’ve seen it occur. Sometimes, there may be only a small patch of cogongrass. The landowner isn’t concerned initially and figures imazapyr is cost-prohibitive.”

So, in trying to find cheaper alternatives to control cogongrass, Williams and colleagues tested many products.

“We wanted to find something effective that landowners would at least try because it isn’t expensive. The one we keep coming back to is a glyphosate/Cogon-X mix. And the glyphosate is the stout formulation — 48 percent, not the stuff you pick up at Wal-Mart, typically.”

The glyphosate is mixed at a quart per acre along with a quart per acre of the Cogon-X. Williams also provides 15 to 20 gallons of water per acre.

“Adding Cogon-X improves the plant take-up of the mix. Instead of taking out 65 percent of the cogongrass with glyphosate alone, we add Cogon-X and kill 85 to 90 percent. That’s a big shift.”

Is the mixture cost-effective? “A Cogon-X/glyphosate mix costs around $35 to $38 per acre. With imazapyr products, you’re probably looking at about $100 to $110 per acre.”

What does Cogon-X actually do? “Cogon-X contains hormone-like compounds in a nutrient base. I’m not a chemist, but I believe herbicides attach to the product and (the target plant) takes it in more willingly. The plant might be fooled by the nutrients in Cogon-X.”

Williams believes the mixture “could be something that’s widely adopted. We’re on the edge, in some ways. There are lots of people trying it and having success. Some landowners with heavy infestations are very happy with Cogon-X results. Florida’s Fish and Wildlife Service tried it last year and is recommending that people use it.”

Williams’ study of Cogon-X is continuing. “We’re checking spraying at different times of the year. The former recommendation was to treat cogongrass in September and October. Well, at that time of year we can be in a drought and spraying does no good if the plants aren’t growing. So we tried it this spring and will try it at intervals throughout the summer.”

Might Cogon-X work with other weeds? “We’re going to try it on climbing ferns and kudzu. Those are at the top of the list. The climbing fern is really becoming a problem in this part of the Southeast. As a climbing vine, it’s hard to get to because the leaves are feathery and they crawl high into the trees. It’s hard to get good coverage with a spray treatment. We’re also looking at spraying a finer mist.”

Williams says there are a couple of things to make sure of when spraying cogongrass:

• Ensure good coverage.

• Be sure the plants are actively growing and not in a drought.

• Remember that the glyphosate/Cogon-X mixture isn’t a release for small trees — either pine or hardwood. Larger trees can be sprayed under but smaller trees can be killed.

• Treat invasive plants when you first notice them. Don’t wait until they grow into a large problem.

e-mail: [email protected]

About the Author(s)

David Bennett

Associate Editor, Delta Farm Press

David Bennett, associate editor for Delta Farm Press, is an Arkansan. He worked with a daily newspaper before joining Farm Press in 1994. Bennett writes about legislative and crop related issues in the Mid-South states.

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