Itchgrass quick facts

What is itchgrass?

Itchgrass or raoulgrass (Rottboellia cochinchinensis) is an annual C4 grass that is considered to be one of the worst weeds in the world. It is especially harmful in agricultural settings.

Itchgrass germinates in the summer and it is most commonly found in tropical or subtropical climates; while best suited to sunny conditions, is relatively tolerant of shade and a wide variety of environmental conditions. It is also often found in sites prone to disturbance, as it easily outperforms native grasses when establishing after a disturbance.

How is itchgrass identified?

Itchgrass can grow to be up to 10 feet (about 3 meters) tall and forms clumps. Its leaves have broad white midribs and are rough to the touch. The leaf sheath has small hairs that can penetrate skin, giving itchgrass its name. Its flowers are arranged in a racemose inflorescence that is around 4 inches (10 centimeters) long.

Where did itchgrass come from?

Itchgrass is native to tropical Africa and Asia to northern Australia. Today, it is present in the U.S., the Caribbean, and Central and South America.

Itchgrass may have been brought to from the Philippines to southern Florida in the early 1900s as a forage grass. It is currently listed as a noxious weed in 12 states in the Southeast and the Midwest, but the full extent of its spread is unclear.

How does itchgrass spread?

Itchgrass seed spreads by seed. The grass is adapted for ant dispersal, and the dispersal units (seed-containing structures) have elaisomes on them. Elaisomes are attractive to ants because they contain proteins and fats. In addition to ants, mature itchgrass seeds can be spread by other animals (livestock, birds), water, and farm equipment. Itchgrass seed can also spread as a contaminant in seeds of agricultural crops.

Itchgrass produces seeds prolifically; one itchgrass plant may produce more than 16,000 seeds. Plants can start producing seeds in as few as six weeks after they appear above the soil surface. 

What are the impacts of itchgrass?

Itchgrass is a major weed in agricultural environments. It is considered a weed for 18 crops, including the grass crops corn (Zea mays), rice (Oryza sativa), sorghum (Sorghum bicolor), and sugarcane (Saccharum), as well as the major legume crop soybean (Glycine max). It grows in dense clumps, and its presence in agricultural settings often significantly reduces crop yields. Managing itchgrass is often costly.

The hairs on itchgrass are unpalatable and cause severe irritation to most grazers, so animals do not eat itchgrass. The hairs can also irritate the skin of agricultural workers.

How can itchgrass be controlled?

Both mechanical and chemical methods are used to control itchgrass; currently, no biological control methods have been developed for itchgrass management, although several have been studied. No single control tactic is effective by itself, but several control methods used together can be effective.

Most commonly, tilling followed by herbicide application is used as a control. Tilling prior to planting agricultural crops encourages the germination of itchgrass. Once the seedlings emerge, they can be sprayed with herbicide. A variety of herbicides can be used, both before and after itchgrass germinates and emerges. Small clumps of itchgrass can also be removed by hand, although this method is not effective at larger scales.

Certain agricultural practices also control itchgrass, such as implementing a crop rotation or planting cover crops. Crop rotation helps control itchgrass because the weed has closer associations with some crops (such as maize) than others. Planting nitrogen-fixing legumes as cover crop is also a way of controlling itchgrass and restoring nutrients to the soil.