Starbur, scientifically known as Acanthospermum hispidum, is a common annual weed recognized by its distinctive, spiny burrs. This plant often becomes a nuisance in gardens, agricultural fields, and other managed landscapes. Its ability to spread widely and its burrs make it a persistent challenge for gardeners and farmers.
Identifying Starbur
Starbur is an annual herb that grows up to 90 cm tall, with a shallow, branched taproot system. Its stems are erect, covered in stiff hairs, and exhibit regular branching, forming a somewhat flat-topped plant. The leaves are arranged in opposite pairs along the stems and are obovate in shape. They are slightly lobed, irregularly toothed, and hairy to the touch.
The flowers of starbur are inconspicuous, yellowish-green, and small. These flowers are found in the leaf axils near the top of the plant. The most distinguishing feature is its fruit, which consists of wedge-shaped achenes grouped into star-shaped clusters. These burrs are covered with numerous short, stiff, hooked spines, and feature two much longer spines at the apex, allowing them to cling to various surfaces.
Understanding Starbur’s Impact
Starbur poses several problems across different environments due to its competitive nature and physical characteristics. In gardens and landscapes, it competes with desired plants for essential resources such as water, nutrients, and sunlight, reducing their growth and vigor. Its presence can also detract from the aesthetic appeal of cultivated areas.
In agricultural settings, starbur can significantly reduce crop yields and contaminate harvests, making them less valuable. It can also interfere with farm machinery during cultivation and harvesting. For livestock, the spiny burrs can cause physical irritation or injury, becoming embedded in wool, fur, or hooves, leading to discomfort or infection and lameness. The burrs readily cling to clothing, skin, and pet fur, making outdoor activities unpleasant for humans.
Controlling Starbur
Controlling starbur effectively involves a combination of manual, cultural, and chemical methods, with timing being an important factor. For small infestations or garden beds, manual removal, such as hand-pulling or hoeing, is effective, particularly before the plants produce burrs. Mulching with organic materials can suppress germination by blocking sunlight and creating a physical barrier.
Cultivation or slashing of infested areas can be beneficial if performed before the plants set seed, which prevents further spread. However, if done after burrs have formed, these actions can inadvertently scatter the seeds and worsen the problem. For larger areas, chemical control with herbicides can be considered. Pre-emergent herbicides are applied before starbur seeds germinate to prevent their emergence, while post-emergent herbicides are used on actively growing plants.
When using chemical controls, it is important to read and follow product labels carefully, ensuring safe and effective application while protecting desirable plants. Using herbicides with different mechanisms of action is recommended to prevent herbicide resistance.
Preventing Future Starbur Growth
Preventing starbur from establishing or returning is a proactive approach that minimizes long-term management efforts. Practicing good garden hygiene is important, including regularly cleaning tools, shoes, and pet fur after being in potentially infested areas to avoid spreading burrs. Using certified, clean topsoil and mulch also helps prevent the introduction of new starbur seeds.
Encouraging a healthy and dense plant canopy in gardens and landscapes can naturally suppress weed growth by outcompeting starbur for light and resources. This can be achieved through appropriate plant spacing and the use of groundcovers. Regularly monitoring areas for new starbur seedlings and addressing them promptly before they mature and produce burrs is important for effective long-term prevention.