Southern Crabgrass (Digitaria ciliaris)

Southern crabgrass (Digitaria ciliaris) is an aggressive grass that likely originated in Asia but is now found throughout the world. It is hardy and adaptable to different soil types, and is often considered an invasive weed, especially in North America and China. If not in an area that threatens crops, however, southern crabgrass can be utilized to stabilize and protect the soil.

I. Appearance and Characteristics 

Digitaria ciliaris is a species of grass known by the common names southern crabgrass, tropical finger-grass, tropical crabgrass or summer grass.

The grass is known as “ගුරු තණ – guru thana” in Sri Lanka.

Digitaria ciliaris is a tough plant, believed to have originated in Asia but now found all over the tropical belt of the planet, as well as in many temperate regions of both hemispheres. This grass is an invasive species considered an aggressive weed in certain countries, including China, Mexico and the United States.

Together with Portulaca oleracea, Ipomoea pes-caprae and Melanthera biflora, Digitaria ciliaris is usually one of the first species colonizing degraded or altered environments in tropical zones of the planet.

This grass is an annual plant that can grow up to 1 m tall but is usually much shorter. The roots are at the nodes and the stems produce runners that allow the plant to grow fast forming scruffy-looking patches about 1 m across and half a metre in height. The leaves are linear to linear-ovate narrowing at the tip to 15 centimeters long. The inflorescence is at the top of a long stem, usually much taller than the leaves, with two to nine 5–10 cm long sub-digitate racemes.

Southern crabgrass, and the related large crabgrass, especially the cultivars ‘Red River Crabgrass’, ‘Impact’, and ‘Quick-n-Big’, have been utilized as a forage crop for livestock, as it is a highly nutritious warm season grass. Red river crabgrass responds well to nitrogen fertilizer, growing up to 3 feet tall, and needs to be in rotation with cool-season forage.

II. How to Grow and Care

Sunlight

Southern crabgrass thrives in conditions of full sun, requiring bright and direct light for optimum growth. This exposure maximizes photosynthesis, promoting healthy development and robustness. While southern crabgrass tolerates partial sun, reduced light levels may result in less vigorous growth and diminished vitality, which can make it more susceptible to pests and diseases. Outdoors, southern crabgrass performs best when planted in open areas where sunlight is abundant. This species has evolved to efficiently capture light, potentially manifesting in more erect growth when light is scarce to optimize its energy intake.

Watering

Thriving in warm, moist conditions, southern crabgrass has adapted to the periodic rainfall of its native subtropical regions. This species is drought-tolerant yet benefits from consistent moisture for optimal growth. Watering every week will maintain its hydration balance without over-saturating the soil. As a plant that flourishes outdoors, southern crabgrass exhibits a robust growth cycle during the rainy season, which significantly influences its watering needs and overall health.

Propagation

A widespread annual grass, southern crabgrass is efficiently propagated through sowing. For optimal establishment, seeds should be scattered on a prepared soil surface, lightly covered, and kept moist to facilitate germination. They are vigorous growers and can thrive in various soil conditions, making them easy to cultivate. Adequate watering and ensuring good soil contact with seeds are critical, enabling southern crabgrass to quickly develop a robust root system. Regular monitoring helps manage growth and allows gardeners to maintain desired coverage.

Transplanting

Transplanting southern crabgrass is ideally carried out in the S2-S3 season, their vibrant growth phase. Choose a location with plenty of sunlight for successful transplantation. Remember, southern crabgrass is a sun-loving plant that thrives best under direct sunlight. Be gentle while handling, it’s worth the extra care!

III. Uses and Benefits 

• The grass is highly nutritious before it exhausts itself producing seed.
• It has a relatively high protein content, so it is commonly planted in fields to provide grazing for livestock.
• Crabgrass can survive both heat and drought, produces a great deal of grain, smothers other weeds, and creates its own mulch. It is an ideal candidate for small-scale farming.

IV. How to Management and Prevention

Management

The first step in managing Digitaria ciliaris is to identify the type of chemical you are using. Pesticides and fungicides come in a wide variety of types, so it’s important to understand which one you are using. For example, some pesticides are systemic, meaning they move through the plant and about-competing it. Others act as contact pesticides, killing pests when they come in contact with them. Knowing your options will help you decide which method is best for your particular situation.

Biological control involves releasing a beneficial insect or fungus into the environment to kill weeds.This method can be effective against small-scale infestations but may not work for large-scale outbreaks.

Prevention

Digitaria ciliaris is a fast-growing, invasive weed. It has been a common problem in the Americas for decades. But it has recently become more problematic on the mainland as well. Digitaria ciliaris can be found at all elevations of mountain regions and is common in disturbed areas, including roadsides, pastures and agricultural fields. In addition to its invasive nature, Digitaria ciliaris poses a threat to native plants by out-competing them for water and nutrients.

• To keep your landscape healthy and beautiful. It is important to remove this weed from your property as soon as possible. Fortunately, there are several ways you can manage this problem without using harmful chemicals or pesticides:
• Use a natural organic herbicide like vinegar or ammonia-based products such as organic herbicides. You can also use glyphosate products such as glyphosate or aminopyralid. Both non-selective herbicides kill everything they come into contact with, including Digitaria ciliaris itself
• Herbicide-resistant weeds can be controlled with another type of herbicide called dicamba which works very differently than glyphosate.