A glyphosate-resistant Palmer amaranth biotype was confirmed in central Georgia. In the field, glyphosate applied to 5- to 13-cm-tall Palmer amaranth at three times the normal use rate of 0.84 kg ae ha−1controlled this biotype only 17%. The biotype was controlled 82% by glyphosate at 12 times the normal use rate. In the greenhouse,I50values (rate necessary for 50% inhibition) for visual control and shoot fresh weight, expressed as percentage of the nontreated, were 8 and 6.2 times greater, respectively, with the resistant biotype compared with a known glyphosate-susceptible biotype. Glyphosate absorption and translocation and the number of chromosomes did not differ between biotypes. Shikimate was detected in leaf tissue of the susceptible biotype treated with glyphosate but not in the resistant biotype.

The anticipated release of EnlistTM cotton, corn, and soybean cultivars likely will increase the use of 2,4-D, raising concerns over potential injury to susceptible cotton. An experiment was conducted at 12 locations over 2013 and 2014 to determine the impact of 2,4-D at rates simulating drift (2 g ae ha−1) and tank contamination (40 g ae ha−1) on cotton during six different growth stages. Growth stages at application included four leaf (4-lf), nine leaf (9-lf), first bloom (FB), FB + 2 wk, FB + 4 wk, and FB + 6 wk. Locations were grouped according to percent yield loss compared to the nontreated check (NTC), with group I having the least yield loss and group III having the most. Epinasty from 2,4-D was more pronounced with applications during vegetative growth stages. Importantly, yield loss did not correlate with visual symptomology, but more closely followed effects on boll number. The contamination rate at 9-lf, FB, or FB + 2 wk had the greatest effect across locations, reducing the number of bolls per plant when compared to the NTC, with no effect when applied at FB + 4 wk or later. A reduction of boll number was not detectable with the drift rate except in group III when applied at the FB stage. Yield was influenced by 2,4-D rate and stage of cotton growth. Over all locations, loss in yield of greater than 20% occurred at 5 of 12 locations when the drift rate was applied between 4-lf and FB + 2 wk (highest impact at FB). For the contamination rate, yield loss was observed at all 12 locations; averaged over these locations yield loss ranged from 7 to 66% across all growth stages. Results suggest the greatest yield impact from 2,4-D occurs between 9-lf and FB + 2 wk, and the level of impact is influenced by 2,4-D rate, crop growth stage, and environmental conditions.

Weed control in organic peanut production is difficult and costly. Sweep cultivation in the row middles is effective, but weeds remain in the crop row, causing yield loss. Research trials were conducted in Ty Ty, GA to evaluate implements and frequencies of cultivation to improve in-row weed control in organic peanut. Implements were a tine weeder and power takeoff-powered brush hoe that targeted weeds present in the row. Frequencies of cultivation were at vegetative emergence of peanut (VE), 1 wk after VE (1wk), 2 wk after VE (2wk), sequential combinations of VE/1wk, VE/2wk, and VE/1wk/2wk. All plots were cultivated with a sweep cultivator to control weeds in row middles. The tine weeder tended to be easier to operate and performed more consistently than the brush hoe. Both implements performed best when initial cultivation was at VE. Delaying the initial cultivation reduced overall effectiveness. Plots with the best in-row weed control were hand-weeded once to control escapes and harvested for peanut yield. The best overall combination of weed control, minimal use of salvage hand-weeding, and maximum peanut yield resulted from sequential cultivation at VE/1wk using either the tine weeder or brush hoe, row middle sweep cultivation, and preharvest mowing.

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 offtarget movement of dicamba has occurred or sprayer contamination is suspected.Key Words: Arachis hypogaea L., crop tolerance, drift, herbicide injury, sprayer contamination.Concerns regarding glyphosate-resistant weeds has led to an interest in developing alternative herbicide-tolerant crops. Dicamba-tolerance is being developed in several broadleaf crops including soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) (Behrens et al. 2007;Subramanian et al. 1997). Currently, dicamba is registered for postemergence broadleaf weed control use in various grass crops such as field corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and wheat (Triticum aestivum L.) (Anonymous, 2011).Dicamba's reputation for off -target movement due to drift and volatility has been well documented (Al-Khatib and Peterson, 1999;Behrens and Lueschen, 1979). In the southeast, peanut is grown in close proximity to both soybean and cotton. Thus, the adoption of dicamba-tolerance in these crops increases the probability of drift, volatilization, and tank contamination problems that could negatively influence peanut development and yield.Peanut response to dicamba has not been well documented. Dicamba applied at approximately 2 g/ha had no effect on peanut yield in one field trial (Prostko et al. 2009). However, other studies on the control of volunteer peanut indicated that peanut is not tolerant of dicamba (York et al. 1994). In a related forage crop, rhizome peanut (Arachis glabrata Benth) yields were significantly reduced by a foliar application of dicamba + 2,4-D (Ferrell et al. 2006). Other systematic studies on the influence of dicamba rate and timing on peanut have not been published in the literature. Therefore, the objective of this research was to quantify the effects of various rates of dicamba, applied at 30, 60 or 90 days after planting (DAP), on peanut yield. Materials and MethodsField trials were conducted at eight locations across the United States peanut belt during 2008. A complete description of these locations is presented in Table 1. Production and pest management practices were followed according to local Cooperative Extension recommendations.All trials were conducted in a randomized complete block design with a three (application timing) by six (dicamba rate) factorial arrangement of treatments. Dicamba timings were 30, 60, and 90 DAP and d...