Research was conducted during 1988 and 1989 in Georgia and Florida to determine the densitydependent effects and critical periods of wild poinsettia interference with peanut. Peanut yield loss ranged from 0 to approximately 50% over the wild poinsettia density range from 0 to 32 plants 9 m−1 peanut row. Predicted peanut yield losses across 2 yr in Georgia were 0, 4, 8, 12, 15, 26, 40, and 54% for season-long wild poinsettia interference at densities of 0, 1, 2, 3, 4, 8, 16, and 32 plants 9 m−1 of row, respectively. Across 2 yr in Florida, predicted peanut yield losses were 0, 9, 14, 22, 30, 37, and 41% for wild poinsettia densities of 0, 1, 2, 4, 8, 16, and 32 plants 9 m−1 row, respectively. Peanuts had to be maintained poinsettia free for 10 wk after peanut emergence to prevent yield loss. Wild poinsettia that interfered with peanut for more than 2 wk after peanut emergence reduced peanut yield.

Studies were conducted in 1988, 1989, and 1992 in Plains, GA to measure effects of paraquat and alachlor on ‘Florunner’ peanut. Peanut treated with paraquat (0.14 kg ai/ha) plus alachlor (3.4 kg ai/ha) applied at vegetative emergence (VE), or paraquat plus alachlor VE followed by paraquat 28 days after emergence (DAE) were compared with a nontreated control. Both herbicide treatments reduced peanut foliage biomass at 65 DAE in 1989 and 1992. Herbicide treatments did not affect foliage biomass 90 DAE in 1988 and 122 DAE in 1989, but paraquat plus alachlor followed by paraquat reduced foliage biomass at 122 DAE in 1992. Pod biomass, measured at 90 and 65 DAE in 1988 and 1992, respectively, was reduced by herbicides. However, pod biomass did not differ among treatments 122 DAE in 1989 and 1992. Percent reflectance from the peanut canopy measured no effects from herbicides in 1988. However, in 1989 and 1992 herbicides applied sequentially reduced peanut canopy development. Peanut treated with a single herbicide and sequentially took longer to mature. Once optimum maturity was reached, peanut yields were not reduced.

Experiments were conducted from 1988 through 1991 to evaluate the effectiveness of imazethapyr alone and in combination with metolachlor for control of yellow and purple nutsedge. Imazethapyr alone at 0.07 kg ha–1 controlled yellow nutsedge irregularly while the addition of metolachlor greatly improved control. Metolachlor preplant incorporated (PPI) followed by imazethapyr at ground-crack (GC) or postemergence (POST) controlled 72 to 96% of yellow nutsedge, whereas a tank-mix of metolachlor plus imazethapyr PPI controlled 85 to 96%. The addition of metolachlor to imazethapyr did not result in any improvement in control of purple nutsedge. Metolachlor plus imazethapyr PPI controlled ≥ 85% of purple nutsedge PPI, whereas imazethapyr POST controlled ≥ 94%.

Field studies in 1990 and 1991 evaluated treatment timings of nicosulfuron and bentazon alone and in mixture for weed control, peanut injury, and yield. The experimental areas were treated with a broadcast PPI application of benefin at 1.68 kg ai ha-1. Nicosulfuron was applied at 40 g ai ha-1 and bentazon at 560 g ai ha-1. Nicosulfuron mixed with bentazon applied 1 wk after crop emergence (WAE) controlled yellow nutsedge 81%. Bentazon or bentazon plus nicosulfuron applied 1 or 3 WAE controlled smallflower morningglory at least 94%. Nicosulfuron controlled sicklepod at least 76% in 1990. However, control of sicklepod was 71% from 1 WAE nicosulfuron application in 1991 and less than 26% for 3, 5, or 7 WAE application. Bentazon controlled Ipomoea spp. at least 70% but did not control Florida beggarweed and sicklepod. Nicosulfuron alone controlled Florida beggarweed and Ipomoea spp. Nicosulfuron reduced early-season peanut growth, but peanut recovered by mid-August. Bentazon reduced nicosulfuron control of Florida beggarweed when applied 1, 3, or 5 WAE, but not 7 WAE. Bentazon mixed with nicosulfuron applied 3 WAE in 1990 reduced weed-free peanut yields compared to nicosulfuron alone. Nicosulfuron and bentazon did not significantly reduce peanut yields under weed-free conditions in 1991.

Field experiments in 1988 and 1989 evaluated five POST herbicides alone or combined for horse purslane control in peanut. Acifluorfen, acifluorfen plus bentazon, pyridate plus 2,4-DB, and lactofen controlled more than 75% when rated up to 26 days after treatment (DAT). However at 67 DAT, acifluorfen alone, acifluorfen plus bentazon or 2,4-DB, or lactofen applied EPOST controlled horse purslane greater than 60% in 1988. In 1989, only 2,4-DB or pyridate plus 2,4-DB controlled horse purslane at least 70% at 116 DAT. Pyridate alone did not control horse purslane adequately.

Pyridate was evaluated alone and as a component in herbicide systems for weed control and peanut tolerance. Pyridate at 1.0 and 1.5 kg ai ha-1 applied postemergence controlled 79 and 96% of Florida beggarweed, respectively. Pyridate was less effective on sicklepod than 2,4-DB. Peanuts exhibited no visible foliar injury or yield reduction with pyridate at 1.5 kg ha-1, the highest rate evaluated. Comprehensive weed control and maximum yield required that pyridate be tank mixed with 2,4-DB at 0.22 kg ae ha-1.

Temporal changes in factors that contribute to the competitiveness of Florida beggarweed in peanuts were studied in 1986 and 1987. Florida beggarweed leaves were unifoliolate to the ninth node and trifoliolate thereafter. Peanuts grew taller than Florida beggarweed until the R-3 stage of peanuts, after which Florida beggarweed height increased logarithmically. Florida beggarweed branching was suppressed by the peanut canopy until the weed overtopped the peanuts. Florida beggarweed dry weight was reduced 80% by peanuts compared with Florida beggarweed grown alone. Peanuts reduced Florida beggarweed leaf area and canopy area. Percent light attenuation as a function of Florida beggarweed canopy area was described by the equation Y = lnX/25.5. Peanut yields in 60 cm of row on either side of a single Florida beggarweed plant were reduced 19%.

Field experiments were conducted from 1983 through 1987 to evaluate various postemergence grass herbicides on bermudagrass in peanuts. Fluazifop, haloxyfop, and SC-1084 applied once effectively controlled common bermudagrass when less than 8 cm tall, but resulted in variable control when applied to bermudagrass 15 cm or taller. Sethoxydim effectively controlled common bermudagrass one of 2 yr. ‘Coastal’ bermudagrass required two applications of BAS 517, fluazifop-P at 0.21 or 0.28 kg ai/ha, and haloxyfop for control of better than 88%. Clethodim and sethoxydim provided poor to fair control, respectively.

Wild poinsettia control in peanut was evaluated following various preplant-incorporated and postemergence herbicide applications. The addition of vernolate or alachlor to a preplant-incorporated treatment of benefin improved wild poinsettia control obtained with treatments of lactofen or paraquat plus alachlor applied at the time of peanut emergence. Lactofen applied postemergence following lactofen plus alachlor applied at the time of peanut emergence provided ≥92% wild poinsettia control and peanut yields equivalent to the handweeded control. Treatments of paraquat plus alachlor applied at the time of peanut emergence followed by acifluorfen (applied once or twice) or paraquat followed by acifluorfen provided good (74 to 100%) wild poinsettia control for up to 12 weeks after planting and peanut yields not different from the handweeded plots. Treatments that did not provide at least 92% wild poinsettia control when evaluated 5 weeks after planting resulted in significant peanut yield reduction compared to the handweeded control.

Studies were conducted in 1989 and 1990 to determine the phytotoxicity of chlorimuron and tank mixtures on ‘Florunner’ peanut. Chlorimuron plus a petroleum oil adjuvant or 2,4-DB was more phytotoxic (P = 0.05) than chlorimuron plus a nonionic surfactant, based on stunting and chlorosis. Chlorimuron mixed with chlorothalonil, chlorothalonil plus sulfur, or esfenvalerate were no more phytotoxic than the standard. Adding sulfur or nonionic surfactant to chlorimuron plus chlorothalonil did not affect phytoxicity. Sequential applications of chlorimuron and 2,4-DB did not completely negate the phytotoxicity of the tank mixture. Despite differences in phytotoxicity, yields were not reduced.

Control of Texas panicum and southern crabgrass with sethoxydim was reduced under field conditions when bentazon, acifluorfen, bentazon + acifluorfen, pyridate, or naptalam plus 2,4-DB was added. The addition of lactofen to sethoxydim did not result in antagonism. Complete control of annual grasses did not appear to be a necessity in order to improve peanut yields. Peanut yields in plots with 70 to 80% control of annual grasses were comparable to those where annual grass control was 99%.