Field experiments were conducted at nine locations in Texas and Georgia in 2005 and 2006 to evaluate peanut tolerance to lactofen. Lactofen at 220 g ai/ha plus crop oil concentrate was applied to peanut at 6 leaf (lf), 6 lf followed by (fb) 15 days after the initial treatment (DAIT), 15 DAIT alone, 6 lf fb 30 DAIT, 30 DAIT alone, 6 lf fb 45 DAIT, 45 DAIT alone, 6 lf fb 60 DAIT, and 60 DAIT alone in weed-free plots. Lactofen caused visible leaf bronzing at all locations. Yield loss was observed when applications were made 45 DAIT, a timing that would correspond to plants in the R5 (beginning seed) to R6 (full seed) stage of growth. At all locations except the Texas High Plains, this application timing was within the 90 d preharvest interval. Growers who apply lactofen early in the peanut growing season to small weeds should have confidence that yields will not be negatively impacted despite dramatic above-ground injury symptoms; however, applications made later in the season, during seed fill, may adversely affect yield.

Research was conducted at eight locations across the United States peanut belt during 2008 to evaluate peanut response to postemergence applications of dicamba. Dicamba was applied at 0, 40, 70, 140, 280 and 560 g ai/ha at 30, 60, and 90 days after peanut planting (DAP). In 5 of 8 locations, peanut yield losses were greater when dicamba was applied at 30 and 60 DAP when compared to 90 DAP. Estimated yield losses for dicamba applied at 40 g ai/ha ranged between 2% to 29%. Estimated yield losses for dicamba applied at 560 g ai/ha ranged between 23% to 100%. These data may aid peanut growers in making appropriate management decisions in situations where off-target movement of dicamba has occurred or sprayer contamination is suspected.

Most peanut ( Arahcis hypogaea L.) production occurs under highly intensive conventional tillage systems. With recent volatility in input prices, reducing tillage trips is a viable way of reducing production costs. However, growers can experience yield loss when switching from conventional tillage to strip-tillage in peanut on certain soil types due to the lack of an elevated bed at harvest time. Studies were conducted to compare standard strip-till with strip-till on two-row raised beds as well as rip and beds prepared in the fall. Comparisons were made on a coarse textured soil at Tifton, GA and a fine textured soil at Plains, GA. The three bed types, with and without wheat cover, were evaluated over two years at both locations. No effects of cover or interactions with bed type were present. At Plains, the rip and bed and raised bed reduced digging losses by 62 and 47%, respectively. Soil compaction within the harvest depth was reduced by 3.3 and 4.7 times by the raised bed and rip and bed, respectively compared to flat strip-till. The rip and bed increased peanut yield by 465 kg ha −1 over flat bed. At Tifton, no significant differences in yield or digging losses occurred between tillage methods. Soil compaction in the harvest depth was reduced by 1.9 and 2.5 times by raised bed and rip and bed, respectively on this coarse soil type. Reduced compaction and digging losses along with increased yield suggest bedding is more important on finer textured soils.

Field studies were conducted to determine runner type peanut response to glyphosate at 80, 160, 240, 320, and 470 g ae/ha applied 75, 90, and 105 days after planting (DAP) at Plains and Ty Ty Georgia in 2006 and 2007. Data collected included seed kernel mass, peanut pod yield, and seed germination. The two-way interaction between DAP and glyphosate rate was not observed for any variable. Data indicated that glyphosate applied at 75 DAP reduced peanut seed mass to 643 mg/kernel, which was less than the 90 or 105 DAP application masses of 669 and 665 mg/kernel, respectively. This could be attributed to the timing of that application when peanut was in the beginning of pod fill or R3 growth stage of development. Peanut physiological response to glyphosate was reflected in peanut seed mass. As glyphosate dose increased, peanut seed mass decreased. Seed masses following glyphosate at 80, 160, 240, 320, or 470 g/ha were 669, 674, 662, 645, and 625 mg/kernel, respectively, as compared to 678 mg/kernel for the nontreated control. When glyphosate was applied at 80 or 160 g/ha, peanut pod yield was similar to the nontreated control. At glyphosate rates of 240, 320, and 470 g/ha, peanut pod yield was reduced to 88, 76, and 64% of the nontreated control. Peanut pod yield was reflective of the reductions in seed mass with increasing glyphosate rate which reduced yield. Seed germination was 96% and greater, which indicated that glyphosate applied at any rate or timing did not affect viability compared to the nontreated control.

Field experiments were conducted to evaluate the emergence and control of Florida beggarweed in peanut. Diclosulam preemergence (PRE), flumioxazin PRE, and imazapic postemergence (POST) were evaluated at three rates, along with paraquat plus bentazon plus 2,4-DB POST, and a nontreated control. These treatments were applied alone, or followed by chlorimuron applied late postemergence (LPOST). Variable Florida beggarweed control (16 to 90%) was observed when flumioxazin PRE, diclosulam PRE, paraquat plus bentazon plus 2,4-DB EPOST, or imazapic POST were applied alone. The pre-harvest population of Florida beggarweed was significantly reduced by the application of any residual herbicide (flumioxazin, diclosulam, or imazapic) alone at any rate either PRE or POST as compared to the nontreated control. Use of the contact treatment of paraquat plus bentazon plus 2,4-DB EPOST alone did not reduce Florida beggarweed populations as compared to the nontreated control. Adding chlorimuron LPOST to any treatment did not reduce Florida beggarweed populations, but provided suppression and reduced the biomass of existing plants. Consistent Florida beggarweed control (86 to 95%) was achieved with combinations of flumioxazin PRE at 105 g ha −1 , diclosulam PRE at 53 g ha −1 , and imazapic POST at 71 g ha −1 followed by chlorimuron LPOST at 9 g ha −1 . The benefit of chlorimuron LPOST was greatest when early season control was least.

Greenhouse experiments were conducted to determine the effect of soil type, residual herbicide, and herbicide rate on peanut seedling development. Diclosulam, flumioxazin, and sulfentrazone were evaluated at three rates in soils with different pH and mineral fractions from Georgia and Texas. Total peanut biomass (mg root plus shoot per seedling) in nontreated soil types were Faceville sandy clay loam > Duval sand > Pelham sandy loam > Brownfield loamy sand > Tremona sand > Tifton loamy sand. Averaged across all soils, total nontreated dry weight biomass was 722 mg plant −1 , with a range of 574 to 841 mg plant −1 , respectively. Averaged across soils, shoot length and shoot and root biomass were greatest in nontreated control > diclosulam > flumioxazin > sulfentrazone; and shoot lengths were greatest in nontreated control = flumioxazin = sulfentrazone > diclosulam. Herbicide rate did not affect peanut development. When soil pH was 7.8 (Tremona and Brownfield), peanut root biomass was significantly reduced to less than 74% of the nontreated control for sulfentrazone, diclosulam, and flumioxazin. For sulfentrazone and diclosulam, this was attributable to an increase in solubility with increasing soil pH that increased that specific herbicides availability for uptake. Soil organic matter and clay content potentially affected flumioxazin soil solution availability which resulted in variations in seedling growth.

Field experiments were conducted to evaluate control method and time of emergence effects on Florida beggarweed competition in peanut. Two day old cotyledon stage Florida beggarweed were transplanted on the day of peanut emergence or 21 days after peanut emergence (DAPE). Treatments were a weed-free check, Florida beggarweed check established at peanut emergence, chlorimuron applied postemergence (POST) 49 or 63 DAPE, Florida beggarweed clipped weekly to the crop canopy after reaching 15 cm in height, Florida beggarweed clipped beginning at 63 DAPE, mowing of Florida beggarweed at 63 DAPE, and paraquat 63 DAPE. In other treatments paraquat was applied 21 DAPE early postemergence (EPOST), or paraquat was applied EPOST followed by chlorimuron 63 DAPE to a Florida beggarweed infested or weed-free treatment. Prior to treatment application, 98% of Florida beggarweed transplanted at peanut emergence survived. When chlorimuron was applied at 63 DAPE, 93% of Florida beggarweed established at peanut emergence survived verses 31% survival for Florida beggarweed established 21 DAPE. This response indicated that maturing Florida beggarweed were tolerant to chlorimuron. Neither mechanical or chemical control methods reduced survival of Florida beggarweed that were transplanted at peanut emergence. Florida beggarweed established 21 DAPE survived when clipped, mowed, or treated with paraquat 21 DAPE followed by chlorimuron 63 DAPE. Peanut yield was significantly reduced by Florida beggarweed established at peanut emergence. Yield was not affected by paraquat EPOST followed by chlorimuron 63 DAPE. Florida beggarweed was controlled effectively with chlorimuron applied 49 or 63 DAPE.

Field studies were conducted in Alabama and Georgia in 2002 and 2003 to determine whether the peanut cultivar that replaced the cultivar Florunner can tolerate earlier applications of the herbicide chlorimuron than what is registered. The application timing restriction of chlorimuron on peanut had been established in the late 1980s with Florunner. In a factorial treatment arrangement, the cultivars AT201, Georgia Green, Viragard, C99R, and Florunner were treated with chlorimuron at 8.75 g ai/ha at 5, 7, 9, or 11 wk after planting. Only the later two application timings are covered by the current registration. Across all 4 yr-location replications, yield was influenced by the main effect of peanut cultivar. C99R was consistently the highest yielding cultivar. Chlorimuron had no effect on yield, regardless of application timing when compared to the nontreated entries in three of the four repetitions (i.e. Plains 2002, Plains 2003, and Headland 2002). Cultivar-based chlorimuron tolerance differences were detected only at Headland in 2003. For this location, chlorimuron applied at 5 wk after planting reduced yield across all cultivars, while application at 7, 9, and 11 WAP had no effect on yield. Results indicate that chlorimuron possesses a yield-reducing risk only when the crop has been stressed by other factors. Assuming that the crop has been stressed, the potential of yield reduction can be avoided only by observing the currently registered application timing. No clear indication was obtained that one cultivar was more tolerant to chlorimuron than another cultivar.

Field trials were conducted in Georgia, North Carolina, and Texas to evaluate the effects of preplant applications of 2,4-D, dicamba, tribenuron, and tribenuron plus thifensulfuron on peanut yield. Herbicides were applied 30, 15, 7, or 0 d before planting (DBP) in conventional production systems in Georgia and Texas, and 28, 21, 14, 7, and 0 DBP in no- and strip-tillage systems in North Carolina. Amine and ester formulations of 2,4-D did not affect peanut yield at any time of application in any state. Dicamba reduced peanut yield when applied at 0 DBP in two of seven trials. Tribenuron did not affect peanut yield regardless of preplant interval. However, tribenuron plus thifensulfuron reduced yields when applied at 7 DBP in one of five trials. These data suggest that 2,4-D, tribenuron, and tribenuron plus thifensulfuron can be safely used for preplant weed control in peanut when applied 7 DBP. Dicamba should be applied a minimum of 15 DBP.

Imazapic, diclosulam, and flumioxazin have been registered for use in peanut since 1996. These herbicides provide substantial residual control of broadleaf weeds in peanut. A comprehensive review was conducted for these residual herbicides to determine their role in future weed control systems in peanuts. Weed control data for research from over 100 experiments conducted from 1990–2000 by Georgia, Florida, and Auburn Universities and USDA-ARS scientists were compiled. Residual herbicide systems evaluated were imazapic postemergence (POST) at 71 g ai/ha, flumioxazin preemergence (PRE) at 70, 87, and 104 g ai/ha, diclosulam preplant incorporated (PPI) and PRE at 18 and 26 g ai/ha, and paraquat plus bentazon early POST (EPOST). Other treatments included the residual herbicides used in combination with paraquat plus bentazon EPOST, for a total of 17 treatments. Regionally important weeds were selected and included: sicklepod, Florida beggarweed, purple and yellow nut-sedge, Ipomoea morningglory species, and smallflower morningglory. Sicklepod control with imazapic alone was 86% (50 tests), 73% (25 tests) with paraquat plus bentazon, and 63% or less with diclosulam and flumioxazin regardless of rate. Florida beggarweed control was 90% (29 tests) with flumioxazin (104 g/ha PRE); 78% (50 tests) with diclosulam 26 g/ha PPI; 72% (72 tests) with imazapic; and 70% (40 tests) with paraquat plus bentazon. Purple and yellow nutsedge control was 90% with imazapic. Yellow nutsedge control was 78% (18 tests) with diclosulam (26 g/ha PRE) and less than 69% with flumioxazin and paraquat plus bentazon. Paraquat plus bentazon increased weed control over residual herbicides alone.

Field studies were conducted during 1997 and 1998 at three different locations in Georgia to determine peanut and weed response to pendimethalin at 1.1 kg ai/ha applied preplantincorporated (PPI) followed by flumioxazin at 71, 87, and 105 g ai/ha applied preemergence (PRE). Other residual treatments combinations with pendimethalin PPI included flumioxazin mixed with metolachlor or dimethenamid PRE, diclosulam PRE, norflurazon PRE, and imazapic applied postemergence (POST). Herbicide combinations that included flumioxazin controlled Florida beggarweed, tropic croton, and small flower morningglory at least 78% or greater. Late season Florida beggarweed control was 90% or greater with pendimethalin PPI plus flumioxazin at 87 to 105 g/ha applied PRE. Pendimethalin plus flumioxazin did not control sicklepod or yellow nutsedge. Smallflower morningglory control with all herbicide treatments was 90% or greater. Entireleaf morningglory control (when used in combination with pendimethalin PPI) increased from 80% with flumioxazin at 105 g/ha to 90% for flumioxazin in combination with metolachlor. Yields were similar for flumioxazin, norflurazon, imazapic, and diclosulam treated peanut.

Field studies were conducted from 1996 to 1998 in Georgia to determine peanut ( Arachis hypogaea L.) and weed response to ethalfluralin (0.8 kg ai/ha) plus diclosulam applied preplant incorporated (PPI) at 9, 18, 26, 35 and 52 g ai/ha. Other treatments included ethalfluralin PPI followed by paraquat plus bentazon (140 and 280 g ai/ha, respectively) early postemergence (EPOST) applied alone or following ethalfluralin plus diclosulam (18 and 26 g ai/ha) PPI, ethalfluralin PPI followed by imazapic (71 g ai/ha) postemergence (POST), and ethalfluralin PPI. Ethalfluralin was applied PPI in all herbicide programs. Diclosulam controlled Florida beggarweed [ Desmodium tortuosum (Sweet) D.C.], sicklepod [ Senna obtusifolia (L.) Irwin and Barneby], and yellow nutsedge ( Cyperus esculentus L.) inconsistently, and POST application of paraquat plus bentazon was needed for acceptable control. However, diclosulam controlled common ragweed ( Ambrosia artemisiifolia L.), tropic croton ( Croton glandulosus Muell-Arg.), wild poinsettia ( Euphorbia heterophylla L.), and prickly sida ( Sida spinosa L.) without the need for POST herbicides. Higher yields were recorded with diclosulam PPI followed by a sequential application of paraquat plus bentazon than herbicide programs not containing diclosulam or diclosulam alone. Diclosulam PPI followed by sequential applications of paraquat plus bentazon provided greater control of sicklepod and prickly sida that resulted in greater yields. Yields from dicosulam PPI followed by paraquat plus bentazon EPOST were equivalent to yields with paraquat plus bentazon EPOST followed by imazapic POST or imazapic EPOST.