Treat thistles to banish orf

UK - July 18, 2011

Getting rid of thistles in sheep pasture reduces the incidence of orf, a virus that can enter animals via abrasions caused when lambs graze too close to prickly weeds.

“Infected sheep develop scabby lesions on non-woolly areas, such as udders, lips and noses,” explains Andy Bailey, principal biologist for Dow AgroSciences.

“Affected ewes are less likely to let lambs suckle, increasing the risk of mastitis; while lambs that can’t suckle do not grow as well as expected.

“Many farmers vaccinate against orf, but there has been a shortage of vaccine this year.  Preventing the virus taking hold by keeping thistle populations under control is sensible on orf-prone farms.”

“Thistles can easily be seen in fields now as they flower – but this is not the right time to treat them with herbicide,” advises Mr Bailey.

“Spraying thistles when they are putting up seed-heads will send herbicide up the plant rather than down into the roots where it is needed to achieve thorough and long-term control,” he says.

“Better to top them and wait for re-growth and then spray a couple of weeks later when they are 25cm high or across.

“A translocated herbicide such as Thistlex, or Pastor where there are other weeds to control as well, will then move down into the roots, as long as the plant is not stressed. Use the correct rate and apply in 300 litres/ha of water for best coverage.

“On hilly pasture or where farmers are worried about losing clover, consider a more targeted approach – applying herbicide through a weed-wiper or spot treat with a knapsack sprayer.”