Managing saffron thistle in pastures with strategic grazing

Abstract

Saffron thistle (Carthamus lanatus L.) is a widespread and troublesome weed in grazing land throughout much of eastern Australia. Conventional control measures are not feasible in much of this area, so the prospect for controlling saffron thistle through strategic grazing with sheep was investigated.

By sowing seeds, and counting seedlings that emerged, we found that as little as 2 cm of pasture cover reduced the number of seedlings that emerged by 96% compared with bare ground. Grazing experiments showed that the survival of saffron thistle rosettes was reduced by 12% in plots that were strategically rested for one month in autumn, followed by grazing at high stocking rates. Grazing in late spring, when plants produced flowering stems, killed 20% of thistles before they set seed. A comparison of thistle density and pasture composition on farms that practice strategic grazing with neighbouring farms that used continuous grazing supported these results. Pastures had few thistles when perennial grasses accounted for over 35% of groundcover. We conclude that grazing management can help control saffron thistle.