Weed profile: Witchgrass
Witchgrass is an annual weed native to North America. Isolated infestations of witchgrass have been recorded in NSW since 1938, but its distribution has increased dramatically in recent years and it is now found across much of central and southern NSW. Masses of windblown seed heads can be seen blocking roads and engulfing houses and sheds. It can be toxic to livestock and is also a confirmed host for Wheat Streak Mosaic Virus.
Witchgrass is often mistaken for the native perennial grass hairy panic (Panicum effusum). Witchgrass leaves are generally wider (5-18 mm) than hairy panic leaves (2-6 mm), and often have wavy edges. The two plants can be distinguished by looking at their ligules. The ligule of witchgrass is a membrane with hair-like structures (cilia) attached to it. The ligule of hairy panic has no membrane, consisting only of the hair-like cilia.
Witchgrass should be grazed with caution as photosensitisation and livestock deaths have been attributed to it. Monitor livestock closely when grazing witchgrass and check daily for signs of photosensitisation, noting the following:
- cattle are more resistant than sheep, and adult sheep are more resistant than weaners
- young actively growing witchgrass is most toxic
- toxicity generally occurs when witchgrass makes up more than 50% of the available feed
- sheep suddenly introduced to witchgrass are more susceptible than sheep that have been gradually exposed to it
Consult your District Veterinarian for more advice.