Tolerance of subterranean clover cultivars and balansa clover to selective herbicides in Tasmania

Abstract

Fifteen cultivars of subterranean clover (Trifolium subterraneum L.) and 1 cultivar of balansa clover (Trifolium balansae Boiss.) were screened for tolerance to 2,4-DB, MCPA-Na salt, MCPA amine, bromoxynil and combinations of these herbicides. The clovers were sprayed at the 3-4 trifoliate leaf stage and dry matter production assessed in the following spring. All herbicides reduced clover dry matter production (DM). The least damaging herbicides to subterranean clover were bromoxynil (0.3 kg a.i./ha) and MCPA-Na salt (0.313 kg a.i./ha) which reduced DM production by 23 and 39% respectively. The most damaging were 2,4-DB (0.8 kg a.i./ha) and MCPA amine (0.313 kg a.i./ha) plus bromoxynil (0.3 kg a.i./ha) which reduced DM production by 62 and 56% respectively. The damage caused by MCPA-Na salt (0.5 kg a.i./ha) plus bromoxynil (0.3 kg a.i./ha) was intermediate, reducing clover production by 44%. Second year seedling regeneration was reduced across all herbicide treatments by 32%. Of the currently recommended cultivars, Trikkala was the most tolerant to herbicides, with an average reduction in DM of 37%. Bromoxynil was the herbicide tolerated best by cvv. Enfield, Karridale, Larisa, Mt Barker and Woogenellup. The most effective weed killing treatments were 2,4-DB plus bromoxynil and MCPA-Na salt (0.5 kg a.i./ha) plus bromoxynil(0.3 kg a.i./ha).