ABSTRACT Weed control is an integral part of peanut ( Arachis hypogaea L.) production systems. Paraquat is a staple postemergence (POST) herbicide used in peanut production in the Southeast US. Inorganic liquid nutrient (ILN) concentrates are liquid fertilizers that are recommended for use by producers in tank-mixtures with paraquat by some distributors. Irrigated and non-irrigated field trials were conducted to quantify the safening effect of ILN in various herbicide tank-mixtures on peanut and determine the suitability as tank-mix replacements for bentazon. Field studies indicated similar POST herbicide responses for peanut injury. Greenhouse experiments evaluated POST paraquat tank-mixtures with ILN for weed control and biomass reduction. Paraquat plus S -metolachlor caused significant leaf burn and stunting. Greatest peanut foliar injury occurred 3 d after treatment (DAT) but was transient. For the irrigated field trial, paraquat plus S -metolachlor plus ILN had similar injury levels as compared to paraquat plus S -metolachlor plus acifluorfen plus bentazon at 22 to 25%. For the non-irrigated field study, the application of paraquat plus ILN had 10% injury compared to paraquat at 22%. While injury was the greatest directly following application, peanut was able to recover with no yield or grade loss for both the irrigated and non-irrigated studies. In the greenhouse study, the effect of ILN varied by weed species and reduced leaf injury on several broadleaf weeds. While the addition of ILN to the various paraquat tank-mixtures initially reduced injury, it did not correspond to increases in yield or grade. The variability in weed control, transient injury mitigation, and no yield increase indicates that Georgia peanut growers will receive no benefit for including ILN in their paraquat tank-mixtures but if needed to improve crop nutrition, ILN will not reduce weed control.

ABSTRACT Picloram (4-amino-3,5,6-trichloropicolinic acid) injury, in the form of leaf roll, is often observed in peanut fields due to short crop rotations, contaminated irrigation water, treated hay, and contaminated livestock waste. Limited data on peanut response to picloram is available. Field trials were conducted near Tifton, GA from 2015-2017 to determine the effects of picloram plus 2,4-D (2,4-dichlorophenoxyacetic acid) on peanut growth and yield. Picloram plus 2,4-D was applied to ‘GA-06G' peanut at four different timings: preemergence (PRE), 30 d after planting (DAP), 60 DAP, and 90 DAP. At each timing, three rates of picloram plus 2,4-D were applied including the following: 1/10 th X (0.18 + 0.67 kg ai/ha); 1/100 th X (0.018 + 0.067 kg ai/ha); and 1/300 th X (0.006 + 0.023 kg ai/ha). A non-treated control (NTC) or 0 rate was included for comparison. Peanut plant density was not influenced by any rate or timing of picloram plus 2,4-D. For peanut injury (leaf roll), a significant rate x timing interaction was observed (P=0.047). At 120 DAP, leaf roll was significant for the 1/10 th X rate applied at 30, 60, and 90 DAP, the 1/100 th X rate applied at 60 and 90 DAP, and for the 1/300 th X rate applied at 90 DAP. When averaged over timing, peanut height at 120 DAP was significantly reduced by the 1/10 th X and 1/100 th X rates. When averaged over rate, peanut height reductions were greatest when picloram plus 2,4-D was applied at 60 DAP. When averaged over timing, only the 1/10 th X rate caused significant yield reductions (11%). When averaged over rate, timing had no effect on yield (P=0.5403). Peanut fields unintentionally exposed to picloram plus 2,4-D rates ≤ 1/100 th X can exhibit typical injury symptoms but most likely will not experience yield losses.

ABSTRACT Recent research on the effects of time of d (TOD) when glufosinate is applied to cotton ( Gossypium hirsutum L.) and several protoporphyrinogen-inhibiting herbicides in soybean ( Glycine max L.) has growers concerned about potential TOD effects on peanut weed control. Consequently, research was conducted in 2015, 2016, and 2017 to determine if TOD influences the performance of peanut herbicides acifluorfen, bentazon, imazapic, lactofen, paraquat, and 2,4-DB. Both non- (bare-ground) and in-crop (peanut) studies were conducted. For non-crop, paraquat plus bentazon plus acifluorfen plus S -metolachlor, imazapic plus S -metolachlor plus 2,4-DB, and lactofen plus S -metolachlor plus 2,4-DB were applied to Palmer amaranth and a non-uniform mixture of annual grasses including Urochloa texana (Buckley), Dactyloctenium aegyptium (L.), Eleusine indica (L.), Digitaria spp. at 7:00, 12:00, 17:00, and 22:00 hr. For in-crop studies, two peanut weed control programs were used and herbicide programs were applied at the same TOD. Herbicides were paraquat plus acifluorfen plus bentazon plus S -metolachlor (EPOST) followed by imazapic plus S -metolachlor plus 2,4-DB, or lactofen plus S- metolachlor plus 2,4-DB (POST). For the non-crop studies, a significant interaction between TOD and herbicide program was observed for the 7 d after treatment (DAT) rating of Palmer amaranth control. Control was reduced with imazapic applied at 22:00 hr. At 14 DAT, there was no TOD effect and control was reduced with all imazapic treatments due to ALS resistance. There was no interaction between TOD and herbicide program for annual grass control. Annual grass control was unacceptable (<50%) with lactofen. For in-crop studies, there was no interaction between TOD or herbicide program. Peanut injury was lower at 7:00 hr and 22:00 hr when compared to other timings. Lactofen was more injurious to peanut than imazapic. Palmer amaranth control was not influenced by timing or herbicide program. A reduction in sicklepod control was observed at the 22:00 hr timing and with lactofen. While TOD influenced peanut injury and weed control, peanut yield was not affected.

ABSTRACT Standard row spacing for peanut ( Arachis hypogaea L.) in Georgia is 91-cm in a single-row pattern. Narrower row spacings are often used in crops grown in rotation with peanut. Therefore, converting peanut to narrower row spacing may be easier and beneficial to some growers if cultivars and seeding rates can be identified that can be grown in narrow rows without a reduction in yield and grade. Based on current University of Georgia recommendations, peanut is typically planted at 19 seed/m with a 91-cm row spacing. Using narrower row spacing and constant seeding rates, increased seed costs would be observed. The objectives of this research were to evaluate the influence of cultivars and seeding rate in peanut planted in 76-cm single rows on yield, grade, and tomato spotted wilt virus ( tospovirus ) (TSWV) incidence. Experiments were conducted in 2008, 2010, and 2014 in Tifton, GA and in 2014 at Camilla, GA. Treatments were comprised of three cultivars (varying each year) and three seeding rates (14, 17, and 19 seed/m). Results indicate that pod yield, grade, and TSWV incidence were not affected by seeding rate. Seeding rate significantly influenced plant density where 14, 17, and 19 seed/m seeding rates resulted in 12.1, 13.2, and 13.8 peanut plants/m, respectively equating to a 9% and subsequent 4% increase in plant density as seeding rate increased. Seeding rate did not affect the rate of canopy closure, but cv. Georgia-12Y and TUFRunner ™ ‘511’ had faster canopy closure than Georgia-06G. Peanut grade (total sound mature kernels) was not influenced by seeding rate, but did differ between cultivars. From these results, it can be concluded that 76-cm single-row can provide adequate yield and grade across multiple seeding rates. In addition, this study confirms that cultivar selection is the primary means for reducing TSWV incidence and altering grade in 76-cm peanut production.

ABSTRACT The increase in herbicide-resistant weeds over the past decade has led to the introduction of crops that are resistant to auxin herbicides. Strict application procedures are required for the use of auxin herbicides in auxin-resistant crops to minimize off-target movement. One requirement for application is the use of nozzles that will minimize drift by producing coarse droplets. Generally, an increase in droplet size can lead to a reduction in coverage and efficacy depending upon the herbicide and weed species. In studies conducted in 2015 and 2016, two of the potential required auxin nozzle types [(AIXR11002 (coarse) and TTI11002 (ultra-coarse)] were compared to a conventional flat-fan drift guard nozzles [DG11002 (medium)] for weed control in peanut herbicide systems. Nozzle type did not influence annual grass or Palmer amaranth control in non-crop tests. Results from in-crop tests indicated that annual grass control was 5% to 6% lower when herbicides were applied with the TTI nozzle when compared to the AIXR or DG nozzles. However, Palmer amaranth control and peanut yield was not influenced by coarse-droplet nozzles. Peanut growers using the coarse-droplet nozzles need to be aware of potential reduced grass control.

ABSTRACT The development of 2,4-D-resistant cotton and soybean cultivars has created great concern about the potential off-target movement of 2,4-D onto sensitive broadleaf crops. Peanut is often grown in close proximity to cotton and soybean. Therefore, field studies were conducted during 2012 and 2013 at Plains, Ty Ty, and Attapulgus, GA to evaluate peanut response to 2,4-D at 67, 133, 266, 533, and 1066 g ae ha −1 applied at preemergence (PRE), 10, 20, or 30 d after planting (DAP), corresponding to PRE, V2, V3, and V5 peanut growth stages. Nontreated controls (NTC) were included for comparison. Treatment timing by rate interactions were significant (P < 0.0001). As 2,4-D rate increased peanut injury increased. There was variation in yield loss response dependent on peanut growth stage at application timing. Peanut that was treated preemergence and at the V2 growth stage did not have yield loss at any of the 2,4-D evaluated rates (67 to 1066 g ha −1 ) relative to the NTC. When peanut was treated at V3 and V5 growth stages with 2,4-D, injury estimates were 5 to 32% from the 67 to 1066 g ha −1 rates respectively, and peanut canopy diameter was stunted 5 to 35% at the same rates. The resulting peanut yield loss was 23 and 36% from 533 and 1066 g ha −1 of 2,4-D applied at V3 and V5 growth stages; in part due to reproductive growth being initiated during that time-frame and peanut had less time to recuperate before harvest. Linear regression models were used to evaluate peanut injury and peanut yield results. Significant correlations were established for V3 and V5 treatments between injury and yield, injury and canopy diameter, and canopy diameter and yield (P < 0.0001), with correlation coefficients of − 0.48, − 0.76, and 0.51, respectively. Growers and extension agents will be able to use these peanut injury estimates and canopy diameter data to make improved predictions of potential peanut yield loss where off-target movement of 2,4-D or sprayer contamination has occurred.

ABSTRACT The development of dicamba-resistant cotton and soybean cultivars has created great concern about the potential off-target movement of dicamba onto sensitive species, including broadleaf crops. Peanut is often grown in close proximity to cotton and soybean. Therefore, field studies were conducted during 2012 and 2013 at Plains, Ty Ty, and Attapulgus, GA to evaluate peanut response to rates of dicamba (35, 70, 140, 280, and 560 g ae ha −1 ) applied at preemergence (PRE), 10, 20, or 30 d after planting (DAP) corresponding to PRE, V2, V3, and V5 peanut growth stages, respectively. Nontreated controls were included for comparison. As dicamba rate increased, both peanut injury and peanut yield loss increased. Peanut response to dicamba was fit to log-logistic regression models for injury and linear regression models for yield loss. Peanut injury increased with rate of dicamba, but was variable among the locations. A general trend was that peanut plants became more sensitive to dicamba injury as plants approached reproductive stage, as evidenced through a declining linear relationship between I 50 values (i.e. rate of dicamba that elicits a 50% crop response) and timing of application. PRE applications of dicamba had I 50 values that ranged from 125 to 323 g ha −1 of dicamba, while I 50 values were 44 to 48 g ha −1 of dicamba at the V5 peanut growth stage. There was a linear relationship between peanut yield and dicamba rate, with 560 g ha −1 causing maximum yield losses ranging from 0 to 86% when applied PRE, 24 to 82% when applied at V2 growth stage, 30 to 95% when applied at V3 growth stage, and 45 to 88% when applied at V5 growth stage. Across all treatments and locations, there was also a negative linear relationship between peanut yield and peanut crop injury, with a decline of 8.5% yield for every 10% increase in crop injury. Growers and their consultants/extension agents can use this peanut injury data to predict potential peanut yield loss from sprayer contamination or off-target movement of dicamba.

ABSTRACT Pyroxasulfone is a residual herbicide developed for use in several agronomic crops such as corn ( Zea mays L.), soybean ( Glycine max L.), wheat ( Triticum aestivum L.), and sunflower ( Helianthus annuus L.). Pyroxasulfone provides effective preemergence (PRE) control of annual grasses and broadleaf weeds, but little is known about peanut cultivar tolerance. Therefore, field trials were conducted in Georgia during 2012 and 2013 to evaluate peanut cultivars ‘Georgia-06G’, ‘Georgia Greener’, and ‘Tifguard’ response to pyroxasulfone applied PRE at 0, 120, or 240 g ai/ha. Greater stunting occurred during 2012 than 2013. Peanut stunting 10 days after planting (DAP) during 2012 and 2013 ranged from 38 to 55% and 3 to 11%, respectively. At 10 DAP, greater injury was observed in ‘Tifguard’ as compared to ‘Georgia-06G’ with pyroxasulfone at 120 g ai/ha. ‘Georgia Greener’ was injured more than ‘Tifguard’ following the 240 g ai/ha rate of pyroxasulfone. By 120 DAP, peanut had recovered substantially from stunting caused by PRE applications of pyroxasulfone with no cultivar interactions. Peanut yield was influenced by pyroxasulfone rate when applied PRE. Peanut yield was 7,140 kg/ha in treatments that did not include pyroxasulfone. Treatments that included pyroxasulfone at 120 g ai/ha yielded similar to treatments without pyroxasulfone. Peanut yield was reduced to 6,750 kg/ha (7%) following pyroxasulfone applied at 240 g ai/ha. When combined over pyroxasulfone rate, ‘Georgia-06G’ produced greater yields than the other cultivars.

ABSTRACT Laboratory and greenhouse studies were conducted to determine the absorption, translocation, dose response, efficacy, and effects on biomass of the herbicide diclosulam on bristly starbur ( Acanthospermum hispidum DC.) In laboratory experiments, 14 C-diclosulam absorption and translocation was evaluated in bristly starbur. Greenhouse studies determined bristly starbur growth response to postemergence applied diclosulam at 0, 0.2, 0.4, 0.8, 1.6, 3.3, and 6.5 g ai/ha. Bristly starbur seed were collected from two Georgia locations, hand cleaned, and grown in the greenhouse. Bristly starbur plants were then foliar treated with diclosulam when plants were in the 4 to 6 leaf stage of growth. 14 C-diclosulam was applied to a single non-treated, most fully developed bristly starbur adaxial leaf, after the rest of the plant was foliar treated with 0.8 g ai/ha of diclosulam. At 24 and 48 hours after treatment, 14 C-diclosulam was translocated acropetally in bristly starbur to the plant apex, with little to no movement to the lower plant parts including lower leaves, stem and roots. For the dose response studies, bristly starbur growth reduction dry weight (GR 50 ) and efficacy (I 50 ) for diclosulam ranged from 0.95 to 0.92 g ai/ha, respectively. Based on these data, bristly starbur susceptibility to diclosulam was due to its translocation to apical growing points within 24 to 48 hours where acetoacetate synthase (ALS) inhibition occurred resulting in eventual plant death. While bristly starbur is controlled with diclosulam rates below the standard use rate of other weeds, the standard field rates in combination with other herbicide mechanisms of action will continue to be recommended to peanut growers to reduce the potential for bristly starbur ALS resistance selection.

ABSTRACT Field experiments were conducted from 2009 through 2011 to evaluate peanut tolerance to postemergence (POST) applications of pyroxasulfone applied alone or in combination with commonly used foliar herbicides. Hherbicide treatments were arranged in a factorial arrangement that included three pyroxasulfone rates (0, 240, and 480 g ai/ha) and four POST application timings [10, 30, 60, and 90 days after planting (DAP)]. Pyroxasulfone applied at 240 or 480 g ai/ha 10 DAP caused 24 and 33% stunting 2 weeks after treatment (WAT), respectively. Regardless of pyroxasulfone rate, peanut stunting following application 30, 60, or 90 DAP was less than 3%. Peanut yield was not influenced by POST applied pyroxasulfone applied alone. In a second experiment, herbicide treatments were applied in a factorial treatment arrangement that included two pyroxasulfone rates (0 and 240 g ai/ha) and six POST herbicide systems [none; paraquat (140 g ai/ha); paraquat (210 g ai/ha) plus bentazon (280 g ai/ha); paraquat (210 g ai/ha) plus bentazon (560 g ai/ha) plus acifluorfen (280 g ai/ha); imazapic (70 g ai/ha); and lactofen (220 g ai/ha)]. Stunting 2 WAT with paraquat applied 10 DAP ranged from 33 to 37% while less injury was observed with lactofen or imazapic. Peanut stunting 9 WAT ranged from 3 to 6% regardless of weed management system. Pyroxasulfone applied in combination with POST herbicides did not reduce peanut yield.