Hurricane clears the way for invasive weed
BY Arlo Kane, private lands biologist
Florida Fish and Wildlife Conservation Commission
Hurricane Michael brought with it not only destruction to homes but also damage to 3 million acres of timber in Florida’s central panhandle. Much of the timber will not be salvageable and most downed timber will have to be raked into piles and burned before the forest can be re-planted. As this reclamation process begins, there is a green monster waiting to raise its ugly head.
Cogongrass – one of the top 10 worst weeds worldwide – will be inadvertently spread by heavy equipment during the post-hurricane cleanup phase. Operations in forested landscapes is one of the most common ways this plant spreads. Cogongrass spreads by rhizomes, which are underground plant stems that send up roots and shoots from its nodes. As equipment runs through a patch of cogongrass, the rhizomes are broken off and transported on tires and other parts of equipment. The disturbed soil is a perfect medium for growing cogongrass. Each piece of rhizome that lands back in the dirt starts a new plant.
The new plant is unlike any other you have encountered in your daily life. It forms dense mats that can spread rapidly. On clay soils, the rhizomes can reach down almost 3 feet deep. These aggressive rhizomes are thought to be the plant’s main means of survival. Cogongrass already covers over 1.25 million acres of forestland in the southeastern U.S. and is increasing every year. I have seen a five-acre patch of cogongrass explode to 40 acres in less than five years.
WHY SHOULD YOU CARE?
As a landowner, you may be wondering why you should care? Cogongrass is an aggressive weed that can choke out even the hardiest native plant, creating a monoculture in the understory of a forest. It can grow up to 5 feet tall and burn hot enough to kill pine trees, making management with prescribed fire difficult and the potential for wildfires destroying your timber stand even greater.
On top of everything else, this is not an easy plant to get rid of. It has been estimated that it may take over five years of treatments with herbicides to control cogongrass. The older the stand, the harder it is to control. The rhizomes have segmented nodes all along the rhizomes. These nodes can close off and prevent herbicides from reaching all of the root. Younger plants have less root system and are therefore easier to treat effectively.
Two herbicides have been shown to be the most effective at treating cogongrass: Imazapyr and glyphosate, which work best when used with a surfactant. Glyphosate is used in the early spring to prevent flowering and is combined with imazapyr in the late fall to kill the plant. Imazapyr is the most effective but it has its dangers. It is soil active and will kill hardwoods. Using it in pine stands year after year can harm the pines as well. In pines, you need to take a year break between applications. Switch to glyphosate in the intervening years.
The most effective treatment is one that starts as soon as the plant appears. As you begin your clean up, be on the lookout for small patches of cogongrass. It’s much easier to control when its young. Cogongrass has a white fluffy seed head in April and May, that is easy to identify. The leaves have an offset mid-rib but so do some other grasses. The rhizomes are the best identifier. They are segmented and have a very sharp tip.
For the next few years, be on the lookout. Cogongrass may not show up right away. If you already have some on your property, it will be spread by logging equipment, so it is unavoidable. Look for new patches and treat it as soon as you can, and you should be able to prevent its spread on your property. This will be a long-term battle, but ignoring cogongrass can be a devastating mistake for a newly planted stand of timber.
If you need financial assistance to treat your cogongrass, the Natural Resources Conservation Service has a program that can help defray some of the costs. Contact your local NRCS district conservationist and ask about the Environmental Quality Incentive Program. To learn more about managing wildlife and habitat on your property, check out our habitat how-to section at the FWC’s Landowner Assistance Program by going to MyFWC.com/LAP. You can also contact a LAP regional biologist for technical assistance.
For more information on how to identify and treat invasive cogongrass, go to http://plants.ifas.ufl.edu/plant-directory/imperata-cylindrica/