What Is Starbur and How to Control This Problem Weed

Starbur, scientifically Acanthospermum hispidum, is a widespread annual weed also known as bristly starbur and goat’s head. Native to Central and South America, this plant has become naturalized in numerous regions globally, including North America, Africa, and Australia. This plant is a problematic weed in various agricultural settings, like cotton cultivation in Brazil, and its effective seed dispersal contributes to its invasive status.

Starbur Identification and Habitat

To identify starbur, look for an upright, branching herb that can reach heights of up to 90 cm, with stems covered in coarse, stiff hairs. Its leaves are arranged in opposite pairs along the stem and are egg-shaped or oval with irregularly toothed edges. The leaves, which can be up to 12.5 cm long, are also hairy and connect directly to the stem.

The plant produces small, pale yellow-green flowers about 6 mm wide that appear singly in the forks of the upper leaves. Following the flowers, the most definitive feature for identification develops: the fruit. These fruits are small, dry burrs that group together in a star-shaped cluster of seven to eight. Each burr is covered in short, hooked spines and is also armed with two longer, sharper spines at the apex.

Starbur thrives in disturbed soils with a preference for full sun. It is commonly found in tropical and subtropical regions, populating areas like overgrazed pastures, cultivated crop fields, roadsides, and neglected gardens. The weed is successful in light sandy soils but can adapt to a wide range of soil types. Its presence is often a sign of poor land management or soil disturbance.

Problems Caused by Starbur

Starbur is an aggressive competitor, robbing desirable plants like crops and forage grasses of water, sunlight, and soil nutrients. This competition can lead to substantial reductions in crop yield; for example, groundnut yields have been observed to decrease by as much as 50% due to starbur infestations. The weed also serves as an alternative host for various crop pests and plant diseases, including tomato leaf curl virus, further impacting agricultural productivity.

Beyond its impact on crops, starbur poses a direct threat to livestock. The plant is toxic to animals, including goats, cattle, and sheep, if consumed consistently over time. The sharp, spiny burrs can become lodged in the wool of sheep, reducing its quality and value. They can also injure the mouths, eyes, and skin of grazing animals, leading to painful infections and lameness.

The structure of the burrs also makes starbur an effective spreader. The hooked spines on the fruit readily attach to animal fur, human clothing, and agricultural machinery. This allows the seeds to be transported over long distances, introducing the weed to new, uninfested areas. The burrs are a nuisance that makes movement through infested areas uncomfortable.

How to Control and Remove Starbur

Managing a starbur infestation is most effective when action is taken before the plant produces its spiny seeds. For smaller, localized patches, mechanical control methods are practical. Hand-pulling or using a hoe to remove young plants can prevent them from maturing. This work must be done while the plants are still in a vegetative stage, as removing them after burrs have formed can inadvertently spread the seeds.

Mowing is not a complete solution for starbur because the plant can regrow and produce seeds below the height of the mower blades. A beneficial long-term strategy is creating a healthy and dense ground cover. Promoting a vigorous lawn or pasture through proper fertilization and watering helps desirable plants outcompete emerging starbur seedlings for resources, naturally suppressing their growth.

For larger infestations, chemical control may be necessary. The use of a post-emergent broadleaf herbicide is effective against starbur. Select a product that is labeled as safe for the area being treated, such as a pasture-safe formulation, to avoid harming desirable grasses. Always adhere to the manufacturer’s instructions for application rates, timing, and safety precautions to ensure effectiveness.