Yield and botanical composition of rhizoma peanut-grass swards treated with herbicides

Weeds are an increasing problem in rhizoma peanut (RP) (Arachis glabrata Be nth.), a warm-season perennial forage Legume. The objective of this field s tudy was to measure the effect of glyphosate [N-(phosphonomethyl)glycine] a t 1.12, 2.24, or 3.36 kg a.i. ha(-1) and triclopyr ([(3,5,6-trichloro-2-pyr idinyl)oxy]acetic acid) at 0.56, 1.12? or 1.68 kg a.i. ha(-1) applied in th e summer on dry matter (DM) yield and botanical composition of weed-infeste d RP-grass swards at 2 and 4 mo after application. Mexican-tea (Chenopodium ambrosioides L.) and cogongrass [Imperata cylindrica (L) P. Beauv.] Here t he most common Heeds. Glyphosate, at all rates, reduced Mexican-tea DM 2 mo after application in both gears. However, substantial recovery of existing MT plants Has observed 4 mo after application at all but the high rate. Gl yphosate had no effect on cogongrass or other grasses in 1995 or 1996. In b oth years, rhizoma peanut DM declined as the rate of glyphosate increased. Some recovery of RP was noted at the low (1.12 kg ha(-1)) rate of glyphosat e by 3 mo after application. Edible DM (RP + other grasses) was reduced due to glyphosate treatment only st the high glyphosate rate. In both years, t riclopyr was effective in reducing Mexican-tea DM 2 mo after application wi th limited recovery of treated plants 4 mo after application. Cogongrass an d other grasses increased in the triclopyr treatments in both years, possib ly due to reduced competition from Mexican-tea Rhizoma peanut DM decreased as the rate of triclopyr increased in 1995 at 2 and 4 mo after application, but this effect was observed only at 2 mo after application in 1996. Tricl opyr application had Little effect on edible DM. but this was a consequence of the substitution effect of other grasses for RP. Both triclopyr and gly phosate can be useful in weed-infested RP stands, but glyphosate at the rat es tested Has not as effective as triclopyr in controlling Mexican-tea.