Weed Management Study of Metsulfuron-resistant Soapbrush (Clidemia hirta (L.) D. Don) in an Oil Palm Plantation

Abstract

These two experiments have confirmed the presence of metsulfuron-resistant biotype of Clidemia hirta in an oil palm plantation in Jerantut, Pahang, Malaysia. An on-site field experiment using various rates of metsulfuron-methyl, showed only 5 per cent and 10 per cent scorching at 120 g a.i per hectare (x4) and 240 g a.i per hectare (x8) respectively at 56 days after treatment. Both imazapyr and trifloxysulfuron, which have the same mode of action with metsulfuron (ALS inhibitor), also showed poor result, 0 per cent control at 56 days after treatment (DAT). Triclopyr and fluroxypyr, which have different mode of action, gave 100 per cent control at 56 DAT. Better control was achieved by fluroxypyr with 83 per cent scorch effect as compared to triclopyr (58%) at 14 DAT. Dose-response test were conducted in the laboratory, by immersing 10 mm diameter leaf discs in a series of concentrations of herbicide solution. The leaf discs immersed in the metsulfuron-methyl solutions at x1, x2 and x4 of the recommended rate resulted only in colour score of 3 and 4, while metsulfuron-methyl at the rate of x8 gave 12 per cent colour score of 2 and 4 per cent colour score of 3. For the other herbicides used, triclopyr and fluroxypyr showed 100 per cent discolouration at recommended rate (555 g and 197 g a.i per ha, respectively) after 24 hours immersion. The appearance of metsulfuron-methyl resistance in C. hirta need more integrated management of the weed to be practiced to prevent further resistance problem in Malaysia. Keywords: Metsulfuron-methyl, Clidemia hirta, herbicide resistance, integrated weed management.