22nd Dec 08, 1:12pm
With warmer weather and more sunshine come Californian thistles and with their massive root system, they are worse than most reports The Gisborne Herald.They can form dense patches that reduce pasture for stock and their root systems mean they can grow back even if all their foliage is removed.
Jamie Thompson from Ravensdown's agrochemical division says farmers can get on top of them if they are dedicated."Controlling Californian thistles takes at least two years if you're doing it right - and forever if you're not." The first thing is do not top them, he says. New shoots draw energy up from huge underground reserves, so chemical applied before flowering doesn't actively move down to the roots, and the plant can regrow.
Once the plant starts to flower, right through until the plant starts to yellow off in late autumn, applying a clopyralid, glyphosate, or metsulphuron which will move with the carbohydrates back into the roots, will kill the whole plant. Since most new plants establish from old plant roots, not from seed, very effective permanent control of the majority of plants is possible with one application. In a pasture situation, glyphosate and metsulphuron will kill grasses as well as the Californian thistles, so the best option is the clopyralid.But, as clopyralids can kill clover, a weed wiper is the best option, except for dense patches of Californian thistles where there is little clover anyway.