Rattleweed is a common name applied to various plants, often recognized by their distinctive seed pods that produce a rattling sound when dry. These plants can sometimes become a concern in agricultural and natural settings, particularly due to their potential impact on animal health. This article explains what rattleweed is, how to identify it, its risks, and management methods to prevent adverse outcomes for livestock and other animals.
Understanding Rattleweed
Rattleweed primarily refers to species within the Crotalaria genus (legume family, Fabaceae). This genus encompasses over 700 herbaceous plants and shrubs, many native to tropical and subtropical regions, particularly Africa. The name “rattleweed” or “rattlebox” comes from the sound of seeds rattling inside their mature, inflated pods when shaken.
While some Crotalaria species are cultivated for fiber, green manure, or even as food crops in certain regions, others have become troublesome weeds that naturalize in disturbed areas. Their widespread distribution, a result of both natural spread and intentional introduction, has led them to be considered noxious or invasive weeds in several areas.
Identifying Rattleweed
Identifying Crotalaria species involves observing specific plant characteristics. These plants are typically annual herbs, growing erect and reaching heights of 60 to 150 centimeters (2 to 5 feet). Their stems are often angular and green, featuring short, appressed hairs.
The leaves are simple and alternate, appearing narrowly oblong or wedge-shaped, with a darker green upper surface and a lighter underside. Crotalaria plants produce showy, pea-like flowers, most commonly bright yellow, arranged in racemes. The fruit develops into a distinctive, inflated, subcylindrical pod, which turns dark brown to black upon maturity and contains numerous seeds that rattle when dry.
Rattleweed Toxicity and Risks
The primary concern with Crotalaria species is their toxicity, mainly due to the presence of pyrrolizidine alkaloids (PAs). These compounds are not directly toxic but are converted into harmful substances in the liver, leading to liver damage. The seeds typically contain the highest concentration of these alkaloids, but all parts of the plant, even when dried in hay, remain toxic.
Animals most susceptible to PA poisoning include horses, cattle, pigs, and poultry, while sheep and goats show a higher resistance, requiring significantly larger amounts for fatal poisoning. Toxicity is often chronic and cumulative, meaning repeated ingestion of small amounts over time can lead to severe liver failure months after exposure. Acute poisoning, though rare due to the plant’s unpalatability, can result in sudden death from severe liver damage.
Clinical signs of poisoning vary but commonly include weight loss, poor appetite, and dullness. Affected animals, especially horses, may exhibit neurological symptoms such as head-pressing, yawning, aimless wandering, or agitated behavior, indicative of hepatic encephalopathy. Other signs can include yellowing of mucous membranes (jaundice), diarrhea, and secondary photosensitization, where non-pigmented skin becomes sensitive to sunlight and develops lesions. Liver biopsy and examination of liver tissue are often used for definitive diagnosis.
Managing Rattleweed
Effective management of rattleweed involves a combination of preventative, cultural, mechanical, and chemical control methods. Preventing establishment is a primary step, which includes maintaining healthy pastures through proper grazing management and ensuring good soil fertility. Avoiding overgrazing helps desirable forage species outcompete weeds.
For existing infestations, cultural control methods can be effective. Mowing the plants before they set seed is important to prevent further spread, as the seeds can remain viable in the soil for many years. Hand-pulling can be suitable for smaller infestations, ensuring the entire plant, including the roots, is removed to prevent re-sprouting. Mechanical methods like tillage can also help disrupt plant growth.
Chemical control, using herbicides, can be considered for larger areas, but careful application is necessary. Broad-spectrum herbicides like glyphosate can be effective, particularly on plants above the water line. Selective broadleaf herbicides, such as triclopyr, are also used. Always read and follow product labels carefully, considering environmental factors like wind and proximity to water bodies. It is advisable to consult local agricultural extension services for specific recommendations and to ensure safe application practices.