Grazing summer weeds
- Summer weeds can provide stock feed.
- Summer weeds can be toxic.
Summer weeds can provide quality feed for sheep, especially when there is no other green feed around. Windmill grass for example has a moderate forage value and has a digestibility of 35-68%. Perennial grasses such as windmill grass maintain some quality feed into summer especially with summer rainfall and when the flowering stage is delayed. Annual grasses such as soft brome (Bromus hordeaceus) and barley grass have moderate digestibility but quickly lose quality as they become reproductive.
Some summer weeds create grazing problems. Caltrop is toxic to sheep and can cause photosensitization (abnormal sensitivity to sunlight) leading to inflammation of exposed skin and sometimes death. If seed set is not prevented, the spiny burrs from infestations can cause lameness and infection, particularly in young lambs because their hoofs are soft.
Crumbweed (Chenopodium pumilio) can also be toxic to sheep causing cyanide poisoning, profuse scouring and sudden death. It emerges in spring and summer and can also reduce crop establishment in the following season (allelopathic). It is native to Western Australia.
In the wetter regions, lesser loosestrife (Lythrum hyssopifolia) can also be a problem. It has been implicated in occasional large mortalities of sheep grazing stubbles in summer. It causes severe hepatic (liver) and renal (kidney) tubular necrosis. It is thought that the late senescence or greenness of this plant in summer stubbles may contribute to its attractiveness to stock during this time. It is a sprawling annual with angular, ribbed stems and pink flowers.