Cogongrass a threat to Southeast agriculture?

Cogongrass in the flowering stage presents a pretty, white background of color. Plant it in a pot and pretty soon it will take over the pot, the yard, the neighbor’s yard, a corn field, etc, etc.

Weed scientists universally agree that cogongrass is a problem farmers in the Southeast don’t want, don’t need and can’t afford. Keeping it as a ‘potential’ threat is an ongoing challenge for farmers and scientists alike.

So far, it appears aggressive herbicide programs used in traditional Southeastern crops like corn, cotton, peanuts, soybeans and tobacco have helped prevent rapid spread of the weed.

However, some well-timed cultural practices and herbicide applications may further decrease the likelihood of cogongrass problems and increase crop productivity. For example, growing a fallow season cover crop has proven highly successful in reducing cogongrass spread.

Tillage can eliminate cogongrass from fields in which new growth occurs. Initial tillage should begin in the spring (March-May) with an implement that inverts the soil to a depth of at least six inches. Additional tillage with a disk harrow or other appropriate implement every 6-8 weeks can further remove the risk. It is important to clean all equipment on site to prevent the spread by rhizomes.

Out of dozens of herbicides tested for significant activity on cogongrass only two, the active ingredients glyphosate (Roundup, Glypro, Accord, etc) and imazapyr (Arsenal, Arsenal AC, and Chopper), have much effect on this grass. Even at high rates and using tank-mix combinations, cogongrass often regenerates within a year following a single application of either product.

Cogongrass is distributed throughout the South and Southeastern United States as far west as eastern Texas. There have been reports of cogongrass surviving as far north as Virginia, West Virginia and Maryland.

It is a fast-growing, highly invasive weed native to Southeast Asia. The once thriving Satsuma orange business along the Gulf Coast of Alabama is the likely culprit for its first introduction into the U.S. in the early 1900s.

Well intended, but poorly planned introductions were later made in Mississippi, where it was once thought to have promise as a livestock forage. In fact, cogongrass has little nutritive value for livestock in large part because it must be fed or processed before its razor sharp leaves mature.

Though it is listed as a toxic weed in most Southern states, few recognize cogongrass, especially in its flowering stage, as a potential threat to farm and forest land.

Clemson University Forestry Professor George Kessler says, “cogongrass is considered one of the 10 worst invasive plant species in the world and has been banned in South Carolina. Despite the ban, cogongrass has been found in seven South Carolina counties.

“It spreads rapidly either through wind-blown seed and underground rhizomes. Once established, cogongrass can choke out native plants, destroy sources of food for wildlife and raise the potential for forest fires,” according to Kessler, who is the South Carolina cogongrass task force leader.

“Growth rates are phenomenal, routinely 10 feet per year just from rhizomes,” Kessler says. “This grass produces a very heavy vegetation mat, when dried under typical summer conditions in the Southeast it produces a highly combustible fire hazard.”

Cogongrass spreads rapidly either through wind-blown seed and underground rhizomes. Once established, it can choke out native plants, destroy sources of food for wildlife and raise the potential for forest fires, according to Kessler.

Cogongrass thrives on fine sand to heavy clay and does well on soils of low fertility.

Attempts at finding natural pests of cogongrass have met with limited success. Pathogens have been isolated, but none have been developed for effective control.

It is a perennial grass that varies greatly in appearance. The leaves appear light green, with older leaves becoming orange-brown in color. In areas with killing frosts, the leaves will turn light brown during winter months and present a substantial fire hazard.

Cogongrass grows in loose to compact bunches, each 'bunch' containing several leaves arising from a central area along a rhizome. The leaves originate directly from ground level and range from 1-4 feet long. Each leaf is one half to three quarters of an inch wide with a prominent, off-center, white mid-rib.

Edges of cogongrass leaves are sharp and distinctly serrated, adding to their noxious nature and lack of value as livestock forage or feed.

Cogongrass is already negatively affecting pine tree nurseries in the Southeast and is a real threat to commercial forest production. Large areas of the weed can disrupt ecosystems, reduce wildlife habitat and can decrease tree seedling growth and establishment

The North Carolina Department of Agriculture and Consumer Services' Plant Industry Division recently implemented a policy change that will prohibit the propagation, nursery cultivation, sale and distribution of cogongrass, along with all cultivars including 'Red Baron' or Japanese blood grass.

State officials are taking aggressive action to encourage nurseries in the state to remove or destroy existing plantings of any of the more popular cogongrass cultivars, including Red Baron or Japanese blood, which has been increasing in popularity as a landscape plant.

Nurseries in North Carolina have until Oct. 31, to remove cogongrass from their facilities. Failure to do so can result in immediate suspension of state nursery licenses.

Though its primary spread in a field or roadside comes from rhizome development and growth, cogongrass can be spread by a tractor driven through a field infested with the weed or by an all-terrain vehicle that has been driven through infested hunting lands.

The cloudlike appearance of cogongrass during the flowering stage may be this invasive plant’s only redeeming virtue. It is already a constant threat to the forest industry in the Southeast and not one that row crop or fruit and tree crop growers can afford to have their land.

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