Studies on growth of Arachis pintoi and its response to herbicides

Seed treatment with solutions of alachlor at 1.92 and 3.84 g/L, metolachlor at 1.44 and 2.88 g/L and oxyfluorfen at 0.36 and 0.72 g/L were less inhibitory to germination and survival of Arachis pintoi seeds than solutions ofametryn at LO and 2.0 g/L, diuron at 1.72 and 3.44 g/L, and pre-mixed hexazinone + diuron at 0.16 + 0.44 and 0.33 + 0.87 g/L which were more phytotoxic. Germination and survival of seeds soaked in contact herbicide solutions of paraquat at 1.2 and 2.4 g/L, glufosinate ammonium at 0.45, 0.9 and 1.8 g/L and sodium chlorate at 29.7 and 39.6 g/L were significantly reduced. Application of post-emergence herbicides to foliage of the legume showed that paraquat at 0.2 kg ai/ha, or 2,4-D dimethylamine at 0.72 and 1.44 kg ae/ha were not significantly phytotoxic while paraquat at 0.4 kg ai/ha, glufosinate ammonium at 0.15 and 0.3 kg ai/ha, premixed ioxynil octanoate + 2,4-D i.w-octyl ester at O.I + 0.6 and 0.2 + 1.2 kg ae/ha, premixed paraquat + diuron at 0.2 + 0.2 and 0.4 + 0.4 kg ai/ha, glyphosate at 0.36 and 0.72 kg ae/ha, imazapyr at O.I and 0.2 kg ae/ha and metsulfuron methyl at 0.015 and 0.03 kg ai/ha were phytotoxic. Further evaluation of 2,4-D dimethylamine showed slight phytotoxicity at 1.44 kg ae/ha while at 2.88 to 7.2 kg ae/ha it was highly phytotoxic. Shading reduced leaf number and fresh weight of the legume. Infield trials, application of alachlor at 1.01 kg ae/ha, metolachlor at 0.72, 1.44 and 2.88 kg ae/ha, and oxyfluorfen at 0.18, 0.36 and 0.72 kg ae/ha as pre-emergence provided almost comparable survival of A. pintoi as untreated, while alachlor at 2.02 and 4,03 kg ae/ha reduced survival of the legume. AH treatments provided good legume coverage of trial plot. Weed coverage was significantly lower in herbicide treated plots compared with untreated plots and weed coverage generally declined with increased herbicide rates. In an open field, growth in biomaas of the newly planted legume increased with time and reached its peak at about 24 weeks after planting. Establishment of the legume at 6, 12 and 16 plants/m2 along planting strips of young rubber generally did not show significant differences in legume coverage up to 12 months after planting.