Photos | Courtesy of University of Southern Mississippi and University of Illinois
Cogongrass can be identified by fluffy white blooms that appear in early spring; by its height, 2-6 feet; its serrated leaf edges; its yellow-green color; and its whitish, off-center mid-rib.
By Carol Williams, Mobile Master Gardener | CoastalAlabamaGardening@gmail.com
Q: I am landscaping my new home site and have a tall, white-blooming grass that seems to be spreading quickly. What might this be and how can I control it?
A: Your yard, like many in Mobile, may be host to one of the seven most noxious weeds in the world: cogongrass (Imperata cylindrica). Also called “Japanese grass,” cogongrass was introduced to the United States through our own Grand Bay in packing materials in 1911. Since then it has spread to over a million acres in Alabama, Mississippi and Florida, and as far west as Texas and east into South Carolina and even Virginia. It is thickest in Alabama in Mobile, Baldwin, Washington, Choctaw, Clarke, Monroe, Escambia and Conecuh counties.
Its seeds and rhizomes spread cogongrass by “hitchhiking” in soil, hay or sod and on farm and mowing machinery. We have also spread it through the sale of Japanese bloodgrass (Imperata cylindrica or “Red Baron”). It reverts to the green and invasive cogongrass so its sale has been made illegal in Alabama and other affected states.
Cogongrass can be identified by those fluffy white blooms that appear here in early spring; by its height, 2-6 feet; its serrated leaf edges, which feel like sandpaper; its yellow-green color, which transitions to red in fall; and its whitish off-center mid-rib. However, its most distinctive characteristic is its rhizomes. They may grow 48 inches into the ground, but most often form a thick mat 6-8 inches deep and compose about 80 percent of its plant matter. The rhizomes end in sharp points that pierce other plant roots, thus killing the competition. If separated from the plant, they can still create new plants weeks later.
This strong underground feature has allowed cogongrass to convert entire forests in infested countries to savanna. In Alabama, the wildlife consequences include reduction of habitat and food for our native and endangered animal species. Its leaf characteristics and a high silica content make cogongrass useless as food for both domestic and wild animals, thus reducing forage on hunting lands.
Frequent mowing at a low height can slow the spread somewhat. In a flower bed or container plant, hand weeding works, but it also must be repeated frequently. When you pull the green leaf, it will readily snap off in your hand, but unless those supporting rhizomes are removed, the grass will resume growing in just a couple of days. Simply tilling cogongrass before overplanting may increase its hold on the area, due to the spreading of broken rhizomes that sprout new colonies of the grass as it recovers from the tilling.
In larger areas, a controlled burn can weaken the plant in the fall, allowing chemical control of the spring regrowth. However, cogongrass contains a resin it that makes it burn at unusually high temperatures and burn larger vegetation, even older trees, not usually affected in a controlled burn. Cogongrass can change a controlled fire into an uncontrolled fire quickly. All precautions must be considered when planning a controlled burn that includes cogongrass.
According to the Alabama Cooperative Extension publication “Cogongrass: Wanted Dead Not Alive” (aces.edu), only two herbicides work on cogongrass: the active ingredients glyphosate and imazapyr. Each can be found in several popular brand names.
For the home gardener, glyphosate 41 percent is probably the best choice as it has no residual soil activity, so the area can be replanted. Imazapyr requires two years or longer before the area can be replanted with replacement species. Read labels before you buy and again before use. In addition to the packaging, labels can be found by searching the internet with the brand name of the herbicide (RoundUp, Arsenal, etc).
Remember, these herbicides are not selective and will affect any green growing material. Protect beneficial species when spraying. In a small area, a piece of cardboard or a plastic crate lid can serve as a useful screen to protect other plants while spraying this grass. A herbicide sponge can also be useful when the grass is growing through a beneficial shrub or plant.
However you choose to eradicate cogongrass, plan to be relentless. If weeding by hand, use a gardener’s fork or other means to dig up the rhizomes, and check the area often. If you spray, keep an eye on the area because multiple herbicide applications will be necessary. If you are planting an area for the first time, make sure you have eradicated any cogongrass before tilling or planting as activity in the soil will encourage the return and spread of it.
If you have a large area already overtaken by cogongrass, the Natural Resources Conservation Service recommends mowing and spraying in fall, August to October. A cover crop of crimson clover or rye grass can be planted for the winter; the cogongrass will return in the spring. At the end of the spring bloom, after it has spent its winter energy stores, cut it low and when it regrows to 12 inches, spray it again. Another fall spraying may be required before planting replacement species. All of this is to ensure the eradication of that underground root mat.
As a gardener, you can help reduce this scourge by managing the cogongrass in your garden and landscape. You can also help locate large infestations by reporting cogongrass to the Alabama Forestry Commission at 334-240-9363. The result will be greater wild animal habitat and cleaner air and water as this invader is controlled.
For more information, contact the Alabama Cooperative Extension Service at aces.edu or the Master Gardener Helpline at 877-252-GROW.
GARDENERS, CHECK THIS OUT
What: Market in the Square (look for the Master Gardener tent for gardening information)
Find: Local produce, homemade bread, jams, preserves, honey, crafts, music
Where: Cathedral Square, Mobile
When: Saturdays through July 28, 7:30 a.m. to noon
What: Mobile Master Gardeners Monthly Meeting
When: Thursday, Aug. 2, 10-11:30 a.m.
Speaker: Terry Plauche, Urban Oases, Green Areas in Metro Areas
MBG: Mobilebotanicalgardens.org for information on fall classes and events
Master Gardener Helpline: Call 877-252-4769, or send gardening questions to firstname.lastname@example.org.