Beware of toxic summer weeds


By Eve Hall
District Veterinarian 

Sheep with photosensitivityWith rain having now fallen in many parts of the region, summer weeds now emerge as a risk for livestock producers. Summer rains have the potential to trigger rapid green growth of plants such as Panicum grass - often referred to as ‘panic’, ‘hairy panic’ or ‘witchgrass - which is commonly found amongst crop stubbles, and which can poison livestock.

When consumed in high amounts, Panicum grasses can cause liver damage and photosensitivity in sheep. Younger stock such as lambs are particularly susceptible.

Signs to look out for include swelling of the face, ears and legs. Affected stock may be very sensitive to sunlight, actively seeking out shade. Scabs similar to sunburn may develop on the head and ears, and significant production losses can occur from liver damage.

Producers should avoid grazing lambs on paddocks containing high amounts of Panicum grasses. Spraying is an option as long as the weed is not grazed straight afterwards when the rising plant sugars cause an increase in palatability and intake. Once the plant has browned off, sheep may prefer to graze other available pasture. However, with any ongoing summer rain, further germination of Panicum grasses may occur.

Other toxic summer weeds of concern include common heliotrope (aka potato weed), which may cause liver damage, and cathead, which can cause a range of symptoms including staggers, sudden death, liver damage and photosensitivity.

For more information about toxic summer weeds or for advice on any stock showing any of the above symptoms, contact Murray Local Land Services to speak with a district veterinarian.

Photo caption: Lamb with photosensitivity - note the swollen face, drooping ears and scabs forming.

Panicum grasses
Panicum spp
AKA ‘panic’, ‘hairy panic’, ‘witchgrass’

Common heliotrope
Heliotropium europaeum
AKA ‘potato weed’, ‘caterpillar weed’

Tribulus terrestis L.
AKA ‘bindi’, ‘caltrop’, ‘three corner jacks’

Young panicumHeliotropeCathead

Mature showing
Mature panicumHeliotropeCathead
Photo source

and Hanwen Wu, DPI

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