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Benghal dayflower (formerly known as tropical spiderwort) is one of the most troublesome weeds in Georgia cotton. Field studies were conducted from 2003 to 2005 to evaluate the relationship between the duration of Benghal dayflower interference and cotton yield to establish optimum weed-control timing. To determine the critical period of weed control (CPWC), Benghal dayflower interference with cotton was allowed or prohibited in 2-wk intervals between 0 to 12 wk after crop planting. Maximum yield loss from Benghal dayflower in May-planted cotton was 21 to 30% in 2004 and 2005, whereas cotton planting delayed until June resulted in maximum yield losses of 40 to 60%. June-planted cotton had a CPWC of 190 to 800 growing degree days (GDD) in 2004 (52-d interval beginning at 16 d after planting [DAP]) and 190 to 910 GDD in 2005 (59-d interval beginning at 18 DAP). In contrast, May-planted cotton in 2005 had a narrower CPWC interval of 396 to 587 GDD (18 d) that occurred 3 wk later in the growing season (initiated at 39 DAP). Mayplanted cotton in 2004 did not have a critical range of weed-free conditions. Instead, a single weed removal at 490 GDD (44 DAP) averted a yield loss greater than 5%. It is recommended that fields infested with Benghal dayflower be planted with cotton early in the growing season to minimize weed interference with the crop. Nomenclature: Benghal dayflower (tropical spiderwort), Commelina benghalensis L. COMBE; cotton, Gossypium hirsutum L.

The effects of chlorimuron application timing on the development of spotted wilt disease of peanut caused by tomato spotted wilt tospovirus was studied in fifteen field trials in Georgia from 2000 through 2007. Chlorimuron at 9 g ai/ha was applied to new peanut cultivars at various intervals ranging from 60 to 105 days after emergence (DAE) under weed-free conditions. When averaged over chlorimuron application timings, AP-3, and Georgia-02C had less spotted wilt incidence than Georgia Green but only AP-3 produced yields equivalent to Georgia Green. AT-201 had significantly higher levels of spotted wilt and 44% lower yields when compared to Georgia Green. Spotted wilt incidence of Georgia-03L did not differ from Georgia Green but the yields of GA-03L were 24% lower than Georgia Green. Differential tolerance of peanut cultivars to chlorimuron was not observed. When averaged over cultivars, chlorimuron applied at 60–69 DAE, 70–79 DAE, or 90–99 DAE increased the incidence of spotted wilt by 6–9%. However, peanut yields were not reduced by any application of chlorimuron.

The phase-out of methyl bromide requires alternative nutsedge management options in vegetable systems. Options that target tuber production, the primary means of reproduction, will be most beneficial. A study was conducted to evaluate the response of purple nutsedge and yellow nutsedge foliar growth and tuber production to a range of glyphosate rates. Glyphosate was applied at six rates between 0.41 and 2.57 kg ae ha−1to 5-wk-old nutsedge plants with multiple shoots. The rate of glyphosate needed to reduce growth 50% (I50) was similar for purple nutsedge foliar growth (0.58 kg ha−1) and tuber biomass (0.55 kg ha−1). In contrast,I50for yellow nutsedge foliar growth was 0.73 kg ha−1, which was greater than theI50for tuber biomass (0.41 kg ha−1). First-order tubers, those directly attached to the initial tuber, had anI50of 0.70 and 0.44 kg ha−1of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. For all higher-order tubers,I50values ranged from 0.29 to 0.60 and 0.14 to 0.30 kg ha−1of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. Glyphosate at 0.74 kg ha−1prevented fourth-order purple nutsedge and third-order yellow nutsedge tuber production (terminal tubers for yellow nutsedge). Fifth- and sixth-order purple nutsedge tuber production was eliminated by the lowest tested rate of glyphosate (0.41 kg ha−1). Effective nutsedge management options will require consistent control between spring and autumn crops. Glyphosate is economical, poses no herbicide carryover issues to vegetables, and minimizes nutsedge tuber production; therefore, it is a suitable candidate to manage nutsedges.

Greenhouse experiments were conducted to evaluate growth and reproduction of Benghal dayflower in response to daily (nondrought stress) and weekly (drought stress) irrigation. With daily irrigation, Benghal dayflower plants added one leaf per plant each week during the initial 6 wk of growth and then increased leaf number eightfold between the intervals of 6 and 10 wk after planting (WAP) and 10 and 15 WAP. By 15 WAP each plant had in excess of 400 leaves. Benghal dayflower plant height increased 2.4 cm wk−1 between 5 and 14 WAP, increasing eightfold during this interval, while plant width increased 20-fold. Aerial spathe formation began between 7 and 8 WAP, with 26 spathes maturing (containing seeds ready for dispersal) each week beginning at 11 WAP. In another study, the influence of duration of drought stress at intervals between 7 and 56 d on early growth and development of cotton and Benghal dayflower was evaluated. Benghal dayflower aboveground biomass was 3.5 times greater than cotton. There was an inverse linear relationship between aboveground biomass and duration of drought stress for cotton and Benghal dayflower, though there was a more rapid decline for Benghal dayflower. A final study evaluated Benghal dayflower response to weekly moisture regimes that approximated 13, 25, 50, and 100% of soil field capacity. Benghal dayflower aerial spathes were 4.6 times more numerous than subterranean spathes. Rate of seed production decreased in a linear manner with decreasing water volume, however, rate of subterranean seed production was less affected by water volume than was aerial seed production. These data indicate that Benghal dayflower thrives under high soil moisture regimes, but that drought stress inhibits growth and reproduction. Cotton appears to be more drought tolerant than Benghal dayflower. Judicious water use in cotton cropping systems in the southeastern United States could be an important component of multiple-tactic Benghal dayflower management program.

Runoff from farm fields is a common source of herbicide residues in surface waters. Incorporation by irrigation has the potential to reduce herbicide runoff risks. To assess impacts, rainfall was simulated on plots located in a peanut (Arachis hypogaea L.) field in Georgia's Atlantic Coastal Plain region after pre-emergence application of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(1S)-2-methoxy-1-methylethyl]-acetamide) and pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine). Runoff, sediment, and herbicide loss as function of strip tillage (ST) versus conventional tillage (CT) were compared with and without irrigation (12.5 mm) after application of an herbicide tank mixture. For the CT system, metolachlor runoff was reduced 2x and pendimethalin 1.2x when compared with the non-irrigated treatment. The difference in irrigated and non-irrigated metolachlor means was significant (P = 0.05). Irrigation reduced metolachlor runoff by 1.3x in the ST system, but there was a 1.4x increase for pendimethalin. Overall results indicated that irrigation incorporation reduces herbicide runoff with the greatest impact when CT is practiced and products like metolachlor, which have relatively low K(oc) and high water solubility, are used. The lower ST system response was likely due to a combination of spray interception and retention by the ST system cover crop mulch and higher ST soil organic carbon content and less total runoff. During the study, the measured K(oc) of both herbicides on runoff sediment was found to vary with tillage and irrigation after herbicide application. Generally, K(oc) was higher for ST sediment and when irrigation incorporation was used with the CT system. These results have significant implications for simulation model parametization.

Multiple Brassica species commonly grown in Georgia were evaluated as a potential alternative to methyl bromide for management of root-knot nematode in vegetables. Brassica species produce general biocides called glucosinolates and were grown as cover crops and incorporated as green manures prior to transplanting of vegetable crop. Nematicidal activity of the Brassica species was based on net changes in nematode population and root damage caused by root-knot infection and feeding. Plant growth and crop yield was also evaluated to determine the response of the subsequent vegetable crop to the incorporated Brassica species. Incorporation of select Brassica species reduced root-knot populations and root damage caused by root-knot infection comparable to non- Brassica species cover crops with metam sodium in most years; however, the level and consistency of the nematicidal activity varied between and within Brassica species. Variations in plant growth and yield were also observed among and with Brassica and non- Brassica species. Generally, increased growth and yield corresponded with cover crop treatments that had the lowest levels of root-knot nematode populations at planting of the subsequent crop. Several cover crop treatments had a negative affect on the growth and yield potential of the vegetable crops. Therefore, a producer will need to choose a Brassica species cover crop that can significantly reduce nematode populations without adversely affecting the growth/yield of the subsequent vegetable crop.

Bengal dayflower (also known as tropical spiderwort) is one of the most troublesome weeds in peanut in Georgia, United States. Field studies conducted in 2004 and 2005 evaluated the relationship between the duration of Bengal dayflower interference and peanut yield in an effort to optimize the timing of weed control. In 2004, the critical period of weed control (CPWC) necessary to avoid greater than 5% peanut yield loss was between 316 and 607 growing degree days (GDD), which corresponded to an interval between June 8 and July 2. In 2005, the CPWC ranged from 185 to 547 GDD, an interval between May 30 and July 3. Maximum yield loss in 2005 from season-long interference of Bengal dayflower was 51%. In 2004, production of peanut pods was eliminated by interference with Bengal dayflower for the initial 6 wk (495 GDD) of the growing season. Robust Bengal dayflower growth in 2004 shaded the peanut crop, likely intercepting fungicide applications and causing a reduction in peanut yield. Therefore, the competitive effects of Bengal dayflower are likely complicated with the activity of plant pathogens. In spite of higher Bengal dayflower population densities, greater Bengal dayflower growth, and greater peanut yield losses in 2004 than in 2005, the CPWC was a relatively similar 4-wk period that ended during the first week of July, for peanut that was planted in the first week of May.

Field studies were conducted in 2002 and 2005 to evaluate autumn vegetable tolerance to residual herbicides applied the previous spring under low-density polyethylene (LDPE) mulch. Spring applications of 1.12 kg/ha S-metolachlor, 0.027 kg/ha halosulfuron, 0.28 kg/ha sulfentrazone, and 1.12 kg/ha S-metolachlor plus 0.027 kg/ha halosulfuron were made under LDPE mulch in March of each year and included a nontreated control. After removal of the spring crop, vegetables were planted the following August. Seeded and transplanted squash, seeded cucumber, transplanted eggplant, and transplanted cabbage were evaluated. Injury to eggplant, cucumber, and transplanted and seeded squash ranged from 8 to 16% for halosulfuron, sulfentrazone, and S-metolachlor plus halosulfuron in 2002, but no injury was observed in 2005. Cabbage injury was less than 5% for any herbicide treatment either year. There were no differences for cabbage biomass for three harvests for any herbicide treatment relative to the nontreated control. Vine length for cucumber and transplanted squash was significantly reduced by sulfentrazone relative to the nontreated control. Eggplant yield for the first harvest was significantly reduced by sulfentrazone as compared with the nontreated control in 2002 but not in 2005. To avoid injury to rotational crops, growers should read all herbicide labels when considering spring herbicide applications under LDPE mulch when autumn vegetable plantings are part of their production scheme to ensure successful crop production. Nomenclature: Halosulfuron; S-metolachlor; sulfentrazone; cabbage, Brassica oleracea L.; cucumber, Cucumis sativus L.; eggplant, Solanum melongena L.; squash, Cucurbita pepo L.

Southern Root-Knot nematode and common cocklebur interfere with cotton growth and yield. A greater understanding of the interaction of these pests with cotton growth and yield is needed for effective integrated pest management (IPM). An additive design was used in outdoor microplots with five common cocklebur densities (0, 1, 2, 4, and 8 plants per plot) growing in competition with cotton, with and without the presence of southern Root-Knot nematode. Differences in cotton height could not be detected among common cocklebur densities or nematode presence at 3 wk after transplanting (WAT); however, differences in crop height were observed at 5 WAT between nematode treatments. In the absence of nematodes, the relationship between cotton yield loss and common cocklebur density was described by a rectangular hyperbolic regression model (P < 0.0001). Maximum yield loss from common cocklebur in the absence of nematodes exceeded 80%. In the presence of nematodes, there was a linear relationship between cotton yield loss and common cocklebur density (P = 0.0506). The presence of nematodes at each common cocklebur density increased cotton yield loss 15 to 35%. Common cocklebur plant biomass was 25% greater in nematode treatments, likely because of the reduced competitiveness of the cotton plants in these plots. This study demonstrates that multiple pests can interact to cause an additive reduction in crop yield.

Nematodes are the most damaging pathogens of cotton and one of the most important pathogens of peanut. Weeds can support nematode reproduction and reduce the effectiveness of crop rotation as a management tool. This study documents the relative host status of tropical spiderwort for (1) the reniform nematode and the southern and peanut root-knot nematodes and (2) the fungal pathogen southern stem rot. A reproductive factor (RF) was calculated for each nematode (final number divided by initial number). Galling was estimated (0–10 scale) for the root-knot species. The southern root-knot nematode reproduced well on tropical spiderwort, with a gall rating of 3.1 and an RF of 15.5. The peanut root-knot nematode also reproduced well on tropical spiderwort, with a gall rating of 2.1 and an RF of 7.2. Trials with the reniform nematode were analyzed independently. In the first trial with the reniform nematode, the RF was 2.4 on tropical spiderwort and 1.4 on cotton. In the second trial, the RF was 3.6 on ...

Centipedegrass is a warm-season turf grass that has increased in popularity in recent years. However, more information is needed on the use of herbicides during centipedegrass establishment from seed, particularly in seed and sod production systems. The intent of this study was to evaluate turf-grass injury and weed control when atrazine, imazapic, imazethapyr, and simazine are applied immediately after seeding centipedegrass. Atrazine and simazine (applied at 1.1, 2.2, and 4.4 kg ai/ ha) injured centipedegrass less than 15% at 5 wk after treatment (WAT) in 2001. Imazethapyr and imazapic (applied at 0.04, 0.07, and 0.1 kg ai/ha) injured centipedegrass between 7 and 13%, 5 WAT, in 2001 and from 30 to 77% in 2002. Herbicide and application rate also affected centipedegrass cover. At 3 WAT, cover decreased with all herbicides as application rate increased. At 12 WAT in both years, centipedegrass cover increased as atrazine application rate increased and imazethapyr application rate decreased. Imazapic and simazine were less consistent, causing increases in cover one year and decreases, or no change, the next. Imazapic controlled Texas panicum 80 to 89% and was more effective than any other herbicide. Atrazine and simazine controlled crowfootgrass better than any other herbicide. Imazethapyr often injured centipedegrass and failed to control weeds. Atrazine effectively controlled grass and broadleaf weeds with minimal centipedegrass injury. Imazethapyr and imazapic were too injurious to permit usage during centipedegrass establishment from seed.

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−1 controlled this biotype only 17%. The biotype was controlled 82% by glyphosate at 12 times the normal use rate. In the greenhouse, I50 values (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. Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats; AMAPA.

Purple and yellow nutsedge are the most troublesome weeds of vegetable crops in the southeast United States. Elimination of methyl bromide use will require alternative management programs to suppress nutsedge growth and interference in vegetables. Polyethylene mulch is an effective barrier for most weeds; however, nutsedges can proliferate in beds covered with polyethylene mulch. The influence of polyethylene mulch on shoot production and lateral expansion patterns of single tubers of purple nutsedge and yellow nutsedge over time was evaluated in field studies. Purple nutsedge patch size was similar in the black mulch treatment and nonmulched control after 8 and 16 wk after planting (WAP). By the end of the growing season, purple nutsedge patch size in the black mulch treatment was nearly twice that in the nonmulched control. At 32 WAP, there were 1,550 shoots in the 16.1 m2 patch in the black mulch treatment and 790 shoots in the 8.1 m2 patch in the nonmulched control. In contrast, yellow nutsed...

Halosulfuron is an alternative to methyl bromide for managing nutsedges (Cyperus spp.) in several vegetable crops. Field studies were conducted to evaluate eggplant growth and yield when halosulfuron was applied through drip-irrigation before transplant at four rates (0, 26, 39, or 52 g·ha–1 a.i.) or following transplant (26 g·ha–1 applied 1, 2, or 3 weeks after transplant) in spring and fall crops in 2002 and 2003. Inverse linear relationships were observed between rate of halosulfuron and eggplant growth and rate of halosulfuron and eggplant yield. Halosulfuron at 52 g·ha–1 reduced eggplant growth (crop height and canopy width) 19% to 22%. Eggplant fruit biomass at the first harvest was reduced 37% to 63% by halosulfuron applied before transplant. Eggplant was capable of recovering from the initial injury and there was no effect of halosulfuron rate on fruit biomass at the final harvest. Total season fruit biomass was reduced ≤4% from halosulfuron at 39 g·ha–1, while halosulfuron at 52 g·ha–1 reduced fruit biomass 33%. Delay in application of halosulfuron to 3 weeks after transplant (WAT) resulted in ≤7% reduction in fruit biomass and number for the entire season. When halosulfuron was applied 1 WAT, fruit biomass at the first two harvests was reduced >33%, however total season harvest from this treatment was >99% of the yield from the nontreated control. This preliminary study indicates that halosulfuron injected through drip tape may have the potential to assist in the replacement of methyl bromide for nutsedge management in eggplant. However, there are many issues that must be addressed and studied before adopting this practice in eggplant.

Tropical spiderwort (more appropriately called Benghal dayflower) poses a serious threat to crop production in the southern United States. Although tropical spiderwort has been present in the United States for more than seven decades, only recently has it become a pest in agricultural fields. Identified as an isolated weed problem in 1999, tropical spiderwort became the most troublesome weed in Georgia cotton by 2003. Contributing to the significance of tropical spiderwort as a troublesome weed is the lack of control afforded by most commonly used herbicides, especially glyphosate. Vegetative growth and flower production of tropical spiderwort were optimized between 30 and 35 C, but growth was sustained over a range of 20 to 40 C. These temperatures are common throughout much of the United States during summer months. At the very least, it appears that tropical spiderwort may be able to co-occur with cotton throughout the southeastern United States. The environmental limits of tropical spiderwort have not yet been determined. However, the rapid spread through Georgia and naturalization in North Carolina, coupled with its tolerance to current management strategies and aggressive growth habit, make tropical spiderwort a significant threat to agroecosystems in the southern United States.

Halosulfuron is a proposed alternative to methyl bromide for managing nutsedges (Cyperus spp.) in several vegetable crops, including cucurbits. Field studies were conducted to evaluate the crop sensitivity to halosulfuron in a spring squash (Cucurbita pepo L.)—fall cucumber (Cucumis sativus L.) rotation from 2000 to 2002. Treatments included application of halosulfuron to the soil surface after forming the bed, but before laying mulch (halosulfuron-PRE), halosulfuron applied through drip irrigation (halosulfuron-DRIP) after forming bed and laying mulch, metham applied through drip irrigation after forming bed and laying mulch, a nontreated control with mulch, and nontreated control without mulch. Each treatment was applied to both direct seeded and transplanted zucchini squash. Halosulfuron treatments reduced squash plant diameter relative to metham, however plant diameters in halosulfuron-PRE (transplant and direct seed) and halosulfuron-DRIP (transplant) treatments were not different from the nontreated control. Halosulfuron-PRE delayed squash fruit production relative to the mulched nontreated control. However, application of halosulfuron-PRE and halosulfuron-DRIP did not reduce squash yield at the conclusion of the season, relative to the nontreated control. Cucumbers were transplanted and direct seeded into previous squash plots and received either an application of halosulfuron-DRIP, or were not treated. Differences in cucumber yields were not detected with second crop treatments. Cucumbers appear to have adequate tolerance to halosulfuron, making it a potential replacement for methyl bromide for nutsedge control. Suppression of early season squash growth by halosulfuron may hinder the adoption of halosulfuron as a methyl bromide alternative for squash.

Tropical spiderwort has recently become the most troublesome weed in Georgia cotton. Most of Georgia's cotton is glyphosate resistant (GR), and glyphosate is only marginally effective on tropical spiderwort. An experiment was conducted at four locations to determine tropical spiderwort control in GR cotton by 27 herbicide systems. Treatments consisted of three early-postemergence over-the-top (POT) herbicide options and nine late–postemergence-directed (LPD) options arranged factorially. Glyphosate POT controlled tropical spiderwort only 53% 21 d after treatment (DAT). Glyphosate plus pyrithiobac or S-metolachlor controlled tropical spiderwort 60 and 80%, respectively. Pyrithiobac improved control of emerged spiderwort, whereas S-metolachlor provided residual control. Pooled over POT treatments, glyphosate LPD controlled tropical spiderwort 70% 21 DAT. Dimethipin mixed with glyphosate did not improve control. Carfentrazone, diuron, or flumioxazin mixed with glyphosate LPD improved control 9 to 15%. MSMA and MSMA plus flumioxazin were 8 and 19% more effective than glyphosate LPD. At time of cotton harvest, systems without residual herbicides at LPD controlled tropical spiderwort 42 to 45% compared with 64 to 76% with LPD treatments that included diuron or flumioxazin.

Florida beggarweed is native to the Western Hemisphere but is naturalized around the world. During the last century, the mechanization of agriculture has transitioned Florida beggarweed from an important forage component to a weed of significance in the coastal plain of the southeast United States. This herbaceous annual is naturalized and found in fields and disturbed areas throughout the southern United States. The characteristics that made Florida beggarweed a good forage crop also make it a formidable weed. This review describes the importance of Florida beggarweed as a weed in the southern United States and the taxonomy of this species and details the distribution throughout the world and within the United States. The ecology of Florida beggarweed and its interactions with crop plants, insects, nematodes, and plant pathogens also are summarized. Finally, management of Florida beggarweed in agricultural systems using cultural practices and herbicides is reviewed. Nomenclature: Florida beggarw...

Greenhouse studies were conducted to evaluate the sensitivity of three commercial cultivars, eight experimental cultivars and common bermudagrass to clethodim, glufosinate and glyphosate. Each herbicide was applied at eight doses. Data were regressed on herbicide dose using a log-logistic curve (R2 = 0.56-0.95 for clethodim, R2 = 0.60-0.94 for glufosinate, and R2 = 0.70-0.96 for glyphosate). The herbicide rate that elicited a 50% plant response (I50) in the bermudagrass cultivars ranged from 0.04 to 0.19 kg ha(-1) clethodim, 0.19 to 1.33 kg ha(-1) glufosinate and 0.34 to 1.14 kg ha(-1) glyphosate. Relative to other cultivars, common bermudagrass was intermediate in its response to clethodim and among the most tolerant cultivars to glufosinate and glyphosate. TifSport was relatively tolerant to clethodim and glufosinate compared with other cultivars, but relatively sensitive to glyphosate. One cultivar, 94-437, was consistently among the most sensitive cultivars to each of the herbicides. While there were differential herbicide tolerances among the tested bermudagrass cultivars, there did not appear to be any naturally occurring herbicide resistance that could be commercially utilized. However, research indicated that breeding efforts should target herbicide resistance that is at least four times the registered use rate. Also, TifSport and Tifway have been identified as suitable representatives of triploid hybrid bermudagrass cultivars to be used to evaluate the success of turfgrass renovation programs.

Movement and biological activity of 1,3-dichloropropene (1,3-D) and chloropicrin applied through drip irrigation in raised beds was investigated at three locations in the southeastern USA. Tests were conducted in fields with dense populations of nutsedge (Cyperus spp), with one location also having a high level of soil nematodes, both of which served as biological indicators of the distribution of effective concentrations of 1,3-D and chloropicrin. Objectives were (1) to gain a better understanding of 1,3-D and chloropicrin movement and the extent of biological activity outside of the wetted bed area, and (2) to examine the effect of application rate, application concentration and subsequent irrigation events on movement and activity of 1,3-D and chloropicrin. InLine, an emulsifiable concentrate containing 60.8% w/w 1,3-D and 33.3% w/w chloropicrin, was injected into polyethylene mulched beds through the drip tubes and water movement in the beds was visualized by adding a blue dye to the injection system. Gas concentrations of 1,3-D and chloropicrin in soil were measured using Gastec detection tubes at different positions relative to the drip tube at 1-4 days after InLine application. After one week, mulch was removed and nutsedge survival evaluated at different positions in the bed. High concentrations of 1,3-D and chloropicrin were measured at the bed center and midway between the bed center and the shoulder, but concentrations were low at the bed shoulder. Width of nutsedge control was significantly greater than width of water movement. Plant-parasitic nematodes were controlled over the entire bed width, but nutsedge re-emerged at the bed shoulders regardless of treatment. Higher application rates and concentrations of 1,3-D + chloropicrin resulted in higher fumigant concentrations in soil air. Irrigations subsequent to application reduced soil air concentrations of 1,3-D and chloropicrin and increased water movement, as did the use of two drip tubes instead of one. The data show that the pesticidal activity of 1,3-D + chloropicrin extends beyond the waterfront and indicate a significant degree of fumigant activity of emulsifiable 1,3-D + chloropicrin. However, unlike plant-parasitic nematodes, nutsedge could not be controlled over the entire bed width, regardless of rate, concentration and volume of water applied.

Soil solarization has been proposed as an alternative to methyl bromide for controlling nutsedges. Little is known, however, about the relationship between soil solarization and nutsedge tuber viability. Combinations of elevated temperatures and durations of exposure were evaluated for their effect on purple nutsedge and yellow nutsedge tuber viability and new tuber production in growth chamber studies. Estimates of the duration of exposure at each temperature that reduced nutsedge growth parameters 50% (TT50) were supplied by log-logistic regression analysis. Nutsedge tuber viability was reduced when temperatures were ≥ 45 C. Relative to purple nutsedge, yellow nutsedge tuber viability had smaller TT50values for 45, 50, and 55 C. Tuber viability TT50at 60 C was similar for both nutsedges. The TT50for production of new purple nutsedge tubers at 50 C was larger than that for yellow nutsedge. However, there were no differences between species in TT50values for new tuber production at higher temperatures. With sufficient durations of exposure, both purple and yellow nutsedge tubers were killed at temperatures ≥ 50 C. However, application of these data to field situations in Georgia may be limited using present technology because the soil temperature cannot be raised to high enough levels for acceptable solarization effects.

The potential weediness of hybrid bermudagrass cultivars in nontarget areas is an important factor when considering the development of herbicide-resistant cultivars. Field studies evaluated the response of common bermudagrass, hexaploid hybrid ‘Tifton-10’, and two triploid hybrid bermudagrass cultivars (‘TifEagle’ and ‘TifSport’) to clethodim, fluazifop-p, glufosinate, glyphosate, and quizalofop-p. Glyphosate was more consistent than clethodim and clethodim plus glyphosate in controlling common bermudagrass. The triploid cultivars were equally sensitive to each of these treatments, whereas Tifton-10 control was highest with treatments that included glyphosate. Variability between years in control of common bermudagrass was attributed to differences in plant size at application, with greater control of smaller plants. All herbicides reduced common bermudagrass plant diameters ≥ 93% in 1999 when grown without a crop. However, in 2001, only herbicide treatments that included two applications of 1.1 kg ai/ha ...

Relationships among weed seed rain, soil seedbank, and seedling recruitment in no-tillage systems were studied from July 1993 to May 1996. Multiple regression analysis indicated that seedling recruitment of only six of the 25 weed species present was correlated with seed rain samples from the previous autumn, spring soil seedbank samples, or a combination of the two. However, seedling recruitment of the dominant annual grasses (yellow foxtail, giant foxtail, and fall panicum in Field 1—1994, Field 2—1995, and Field 3—1996, respectively) was related to seedbank populations or a combination of seedbank and seed rain densities. These grasses accounted for at least 32% of the emerged seedlings, 12 to 78% of the seedbank, and 16 to 77% of the seed rain. Seedling recruitment of large crabgrass and two broadleaf species, Virginia copperleaf and wild carrot, also were described by seedbank densities or a combination of seedbank and seed rain densities. However, both the broadleaf species were minor compo...

Greenhouse studies were conducted to evaluate halosulfuron tolerance of several squash and cucumber cultivars commonly grown in Georgia. There was an inverse linear relationship between squash plant biomass and rate of halosulfuron (r2 = 0.70 to 0.92). With the exception of ‘Supersett’, the slopes from regression of all squash cultivars were equivalent. The estimated amount of halosulfuron required to reduce growth by 20%, based on regression, ranged from 8.2 to 45 g ai/ha (for Supersett and ‘Dixie’, respectively). Squash plant height was also reduced by halosulfuron, though plants began to recover from the injury by the end of the study. There was no effect of halosulfuron rate on cucumber plant biomass or height. Cucumber cultivars appeared to be more tolerant to halosulfuron than did squash cultivars. Nomenclature: Halosulfuron; cucumber, Cucumis sativus L.; squash, Cucurbita pepo L. Additional index words: Cyperus esculentus, Cyperus rotundus, methyl bromide alternatives, MON 12037, purple nutsedge, v...

Metam sodium alone and in combination with 1,3-dichloropropene plus 17% chloropicrin (1,3-D+C-17) were evaluated under polyethylene mulch film as alternatives for methyl bromide in tobacco and tomato transplant production for both efficacy against pests and crop safety. Eight different weed species, 10 genera or species of fungi and several agronomic criteria were evaluated at three different sites. In general both the metam sodium alone and in combination with 1,3-D+C-17 were highly efficacious when compared to methyl bromide. Short polyethylene film retention times and short aeration times resulted in poor stands and poor crop vigor while relatively long polyethylene film retention times and long aeration periods at the same rates typically resulted in high stand counts and vigor. Combination treatments were more phytotoxic to germinating seed of tobacco and tomato. Vigor and stand counts of the seedlings were higher as aeration time increased, suggesting phytotoxic residues dissipate with time. Method of application of metam sodium, either injected with chisels or sprayed onto the soil surface and incorporated with a tractor-powered tiller alone or co- applied with 1,3-D+C-17 chisel injected, did not affect the efficacy of the treatments. Caution regarding phytotoxicity must be exercised when seeding into soil fumigated with metam sodium alone or combined with 1,3-D+C-17. Additional work will be required to establish safety periods required prior to transplanting crops into fumigated soil.

A survey of county extension agents was conducted in 1998 to determine the most troublesome weeds in corn, cotton, forages and pastures, peanut, small grains, soybean, tobacco, and vegetables in Georgia. The most troublesome weed statewide averaged over all crops was sicklepod. It was the most troublesome weed in cotton and soybean and among the four most troublesome weeds in corn, peanut, tobacco, and vegetables. Sicklepod was found in each of the nine climatological districts and in all the crops surveyed. Perennial nutsedge species were the second most troublesome weeds in Georgia. They ranked as the most troublesome weeds in tobacco and vegetables and were among the top five most troublesome weeds in corn, cotton, peanut, and soybean. Pigweed species were ranked third averaged over all the crops surveyed and were the second most troublesome weeds in cotton and vegetables and among the top five most troublesome species in corn, soybean, and tobacco. Morningglory species were listed as troublesome in si...

Field studies were conducted to evaluate potential methyl bromide alternatives against multiple pests in a bell pepper (Capsicum annum L.) – squash (Cucurbita pepo L.) cropping sequence. Early in the growing season, the most effective treatments in suppressing purple nutsedge (Cyperus rotundus L.) emergence through the polyethylene mulch were methyl bromide, methyl iodide, and chisel-injected 1,3-dichloropropene plus chloropicrin [1,3-D+C35 (chisel)]. However by the end of the season in 1999, only methyl bromide treatment had less purple nutsedge emerging through the polyethylene than the nontreated control. Each soil-applied treatment resulted in nematode-susceptible pepper plants with lower root-gall indices [Meloidogyne spp. (root knot nematode)] than the nontreated control, while there were no differences among treatments with the nematode-resistant pepper cultivar. Total fungi isolated from soil was lower in all treated plots relative to the nontreated control, with the exception of methyl iodide. However, methyl bromide was the only treatment that was consistently effective against Pythium spp. and Fusarium spp. A treatment of metham prior to planting squash was beneficial in reducing root-gall indices in plots treated with 1,3-D+C35 (chisel) and methyl bromide prior to the pepper crop. Methyl bromide, methyl iodide, and 1,3-D+C35 (chisel) applied before pepper resulted in squash with lower root-gall indices than the nontreated control. Glyphosate applied between the first and second crop eliminated exposed weed foliage through the polyethylene mulch, possibly muting the effects of the second crop treatment on weed densities. Results of this study indicate that there are some potential methyl bromide alternatives available to growers for use in pest control, however there does not appear to be one broad-spectrum pesticide that will replace methyl bromide. Also, an effective control for nutsedge species within the pepper–squash cropping system is still elusive.

Metham has been reported as an acceptable weed control alternative to methyl bromide. However, modified application equipment is required to allow its effective use in crops that are grown on polyethylene-covered seedbeds. A power tiller was modified using commonly available materials to apply metham in a 61-cm band and shape seedbeds for laying a black polyethylene tarp. Additional modification allowed the implement to be used in strip tillage and conventional tillage systems. Metham applied using this modified power tiller effectively controlled many species of weeds, including yellow nutsedge, in transplanted watermelon. Nomenclature: Metham; yellow nutsedge, Cyperus esculentus L. CYPES; watermelon, Citrullus lanatus (Thunb.) Mansf. Additional index words: Alternatives to methyl bromide, fumigation. Abbreviations: PPI, preplant incorporated; PRE, preemergence; PTO, power take-off.

There is little information published on patch expansion of perennial weeds and none for Apocynum cannabinum. Studies were conducted to measure the between-season and in-season expansion patterns of natural A. cannabinum patches over three growing seasons. Regression analysis indicated strong relations between patch area in consecutive years 1996 to 1997 (r2 = 0.81) and 1997 to 1998 (r2 = 0.76). Patches less than 20 m2 in 1996 increased in area by more than 100% in 1997 during a fallow season. However, patches decreased in size 6 to 51% between 1997 and 1998 when Glycine max was grown. Evidence suggested that a late-season mowing of the A. cannabinum patches in 1997 contributed more to the decline in patch area than competition from G. max during the 1998 season. The relations between patch area and growing degree units (r2 = 0.97) indicated that greater than 89% of the terminal patch expansion occurred prior to the accumulation of 435 growing degree units (GDU) (June 19, 1997; May 31, 1998; June...

Field studies were conducted in three site-years to measure no-till Glycine max yield loss in relation to Apocynum cannabinum vegetative shoot density. Apocynum cannabinum densities of 28 to 40 shoots m−2 reduced predicted G. max yield 58 to 75% and 62 to 94% with the rectangular hyperbolic and linear regression models, respectively. Differences between locations were attributed to rainfall and temperatures, with delayed G. max canopy closure and higher yield loss where soil moisture remained high and temperatures were relatively cool. Application of these predictive G. max yield loss equations to field populations of A. cannabinum showed that between 19 and 36% and 20 and 29% G. max yield loss could be expected from within A. cannabinum patches for the rectangular hyperbolic and linear regression models, respectively. The rectangular hyperbolic regression model appeared to describe the relation between G. max yield loss and A. cannabinum density accurately; however, the model appeared to be domi...

Apocynum cannabinumis a native creeping perennial distributed throughout the U.S., with increasing importance in reduced tillage systems throughout the Midwest.Apocynum cannabinumhas been shown to be a difficult species to control in field crops. Effective weed management is often a function of the timing of control practice. Knowledge of weed emergence patterns may be useful in predicting the optimum time of weed management. The objectives of these studies were to describe how temperature and moisture affectA. cannabinumseed germination and to describe the relationship between growing degree units (GDU) andA. cannabinumvegetative shoot emergence. At constant temperatures, seed germination was described as a sigmoidal function of temperature (r2= 0.83), with maximum germination (32%) from 26 to 34 C. Under alternating temperatures, seed germination increased in a linear relationship between mean temperatures of 15 and 34 C (r2= 0.85). Maximum seed germination (88%) occurred at a mean temperature of 34 C under alternating temperatures. The relationship between seed germination and osmotic potential between −1.0 and 0 MPa was described by a gompertz function (r2= 0.98). Germination at −1.0 MPa was 4% and increased in a near linear manner to the nontreated control (0 MPa), which had 80% germination. Vegetative shoot emergence in 1997 and 1998 had a sigmoidal relationship to GDU using a base temperature of 6 C (r2= 0.96). However, initial shoot appearance was not consistent over years, with first emergence recorded on May 21, 1997 (132 GDU), and May 5, 1998 (73 GDU). Approximately 50% of the shoots emerged before June 7, 1997 (282 GDU), and May 21, 1998 (285 GDU); therefore, optimal weed management programs will need to be initiated following this GDU accumulation.

The objectives of this study were to determine how the timing of weed management treatments in winter wheat stubble affects weed control the following season and to determine if spring herbicide rates in corn can be reduced with appropriately timed stubble management practices. Field studies were conducted at two sites in Ohio between 1993 and 1995. Wheat stubble treatments consisted of glyphosate (0.84 kg ae/ha) plus 2,4-D (0.48 kg ae/ha) applied in July, August, or September, or at all three timings, and a nontreated control. In the following season, spring herbicide treatments consisted of a full rate of atrazine (1.7 kg ai/ha) plus alachlor (2.8 kg ai/ha) preemergence, a half rate of these herbicides, or no spring herbicide treatment. Across all locations, a postharvest treatment of glyphosate plus 2,4-D followed by alachlor plus atrazine at half or full rates in the spring controlled all broadleaf weeds, except giant ragweed, at least 88%. Giant foxtail control at three locations was at least 83% when a postharvest glyphosate plus 2,4-D treatment was followed by spring applications of alachlor plus atrazine at half or full rates. Weed control in treatments without alachlor plus atrazine was variable, although broadleaf control from July and August glyphosate plus 2,4-D applications was greater than from September applications. Where alachlor and atrazine were not applied, August was generally the best timing of herbicide applications to wheat stubble for reducing weed populations the following season.

Understanding patterns of weed seedling emergence within a growing season and over years is important to develop models to predict optimum timing of weed management practices. A study was conducted in a field with no previous velvetleaf infestations to describe emergence patterns following seed burial at three depths in two tillage systems. Freshly harvested velvetleaf seeds were planted 0, 2, and 6 cm deep in moldboard plowed (MP) and no-tillage (NT) corn stubble in October 1990. Velvetleaf seedling emergence was monitored over the following 4 yr in continuous corn. Emergence was higher in NT than in MP plots throughout 4 yr of observation. The first growing season following seeding, emerged seedlings represented 9.3 to 15.8% of the seeds sown in NT, compared with 0.1 to 0.8% of seeds sown in MP. After four growing seasons, emerged seedlings were 12.5 to 25% of seeds sown in NT but only 6 to 7.4 % of seeds sown in MP. Emergence was consistently higher from the 0-cm depth than from the 6-cm depth in NT, but seeding depth did not influence emergence in MP due to mixing of the soil during tillage. Velvetleaf emergence was related to growing degree days (base 7.5 C), with greater consistency in NT than in MP. Averaged over years and planting depths, 50% velvetleaf emergence occurred within 8 and 13 d of the predicted date in NT and MP systems, respectively.

Experiments were conducted to test the accuracy of a global positioning system (GPS) in measuring the area of simulated weed patches of varying size and to determine the accuracy in navigating back to particular points in a field. Circular areas of 5, 50, and 500 m2 were established and measured using point and polygon features of a GPS. The GPS estimations of the area of those patches had errors ranging from 7 to 45%, 6 to 15%, and 3 to 6%, respectively, when compared to actual measurements. As patch size increased, errors decreased. A curve describing the relationship between GPS error and patch size had an excellent fit (r2 = 0.92). The error remained the same in all measurements across all patch sizes, but composed a smaller percentage of large patches. The GPS had submeter accuracy in navigation to the correct quadrat 73% of the time, located the correct quadrat 27% of the time, and invariably navigated to within 1.58 m of the correct quadrat. The relationship between patch size and measurement error was applied to natural infestations of hemp dogbane.

Experiments were conducted in 1991 and 1992 to evaluate the weed control effectiveness from several rates of AC 263,222 applied PPI and PRE (36 and 72 g ai/ha), early POST (EPOST) (18, 36, 54, or 72 g/ha), POST (18, 36, 54, or 72 g/ha), and EPOST followed by (fb) POST (27 fb 27 g/ha or 36 fb 36 g/ha). These treatments were compared to the commercial standard of bentazon at 0.28 kg ai/ha plus paraquat at 0.14 kg ai/ha EPOST fb bentazon at 0.56 kg/ha plus paraquat at 0.14 kg/ha plus 2,4-DB at 0.28 kg ae/ha. Application method had little effect on weed control with AC 263,222. In contrast, application rate affected control. Purple nutsedge, yellow nutsedge, prickly sida, smallflower morningglory, bristly starbur, common cocklebur, and coffee senna were controlled at least 82% with AC 263,222 at 36 g/ha (one-half the maximum registered use rate) regardless of application method. AC 263,222 at 72 g/ha (registered use rate) controlled sicklepod 84 to 93%, Florida beggarweed 65 to 100%, andIpomoeamorningglory species 89 to 99%. A single application of AC 263,222 at 36 g/ha or more controlled all weeds (with the exception of Florida beggarweed) as well or greater than sequential applications of bentazon plus paraquat fb bentazon, paraquat, and 2,4-DB. All rates of AC 263,222 applied POST and all application methods of AC 263,222 at 72 g/ha had better yields than the pendimethalin control.

A field study was conducted in 1994 and 1995 to determine the effect of MON 12037, linuron, and ametryn on purple nutsedge density in field corn in a 2-yr rotation with cotton. Each corn treatment included cultivation and noncultivation. A standard treatment for purple nutsedge control was applied to all cotton plots in the second season of the corn–cotton rotation. Purple nutsedge shoot densities were reduced in cultivated MON 12037, noncultivated MON 12037, and cultivated ametryn in the corn–corn and corn–cotton rotations. Purple nutsedge tuber population was reduced in the corn–corn rotation by MON 12037 with and without cultivation, cultivated linuron, and cultivated ametryn treatments relative to the noncultivated check. In the corn–cotton rotation, purple nutsedge tuber population was reduced only by the cultivated MON 12037 and cultivated ametryn treatments relative to the noncultivated check.

The Southern Weed Science Society has conducted an annual survey of the most troublesome weeds in several major crops since 1971. The objective of this summary was to characterize shifts in weed populations over a 22-yr period in four major agronomic crops. For corn, soybean, cotton, and peanut, the largest increases in rank as the most troublesome weeds were found with sicklepod and bermudagrass. The largest decreases were found with johnsongrass, crab-grasses, and common cocklebur. Morningglories and nutsedges remained relatively constant weed problems over the 22-yr period. Sicklepod, nutsedges, and morningglories were the three most troublesome weeds averaged over all crops because they are so well established and relatively difficult to control. Pigweeds (Palmer amaranth, sandhills amaranth, tumble pigweed, and water-hemps) have become increasingly important in soybean, peanut, and cotton in a limited number of states.

The introduction of glyphosate-resistant cotton for production in the southeast United States changed herbicide application strategies and increased the profitability of no-tillage and striptillage techniques. Glyphosate (N-[phosphonomethyl]-glycine) is a highly effective herbicide that controls a broad spectrum of annual and perennial grass and broadleaf weeds in cotton [3, 37]. When glyphosate-resistant cotton varieties were first introduced, glyphosate was applied two to four times on most fields and may have been the only herbicide used [4, 5]. In Georgia, 93% of the cotton acres received at least one glyphosate application in 2005 [3]. The technology allowed growers to reduce or eliminate soil-applied herbicides, allowing them to abandon cultivation and make the transition to conservation tillage, which promotes soil conservation and compliance with USDA Federal regulations. Greater than 50% of Georgia cotton was produced using no-tillage or strip-tillage techniques in 2007, a strategy that has been affected by glyphosate weed control [1, 11].

Field experiments were established at Columbus and near South Charleston, OH to determine the effects of giant ragweed population density on soybean yield and to characterize the development of giant ragweed grown in 76-cm soybean rows. An economic threshold was calculated for Ohio using a common treatment for giant ragweed control in soybean. A cost of $41/ha was estimated for a farmer to apply 0.56 kg/ha bentazon plus 0.28 kg/ha fomesafen plus COC (1.25% v/v). Assuming a soybean value of $0.22/kg, the cost of control was equivalent to 5.4 and 7.1% of the soybean yield in 1991 and 1992, respectively, which corresponded to the yield loss caused by 0.08 and 0.03 giant ragweed plants/m2. The competitiveness of giant ragweed can be at least partly attributed to its ability to initiate and maintain axillary leaves and branches within the shaded confines of the soybean canopy.

Experiments conducted from 2007 to 2009 evaluated germination of 11 peanut runner-type cultivars. Germination was evaluated in Petridishes incubated over a thermal gradient ranging from 14 to 30°C at 1.0 C increments. Beginning 24 hr after seeding, peanut was counted as germinated when radicles were greater than 5 mm long, with removal each day. Germination was counted daily for seven days after seeding. Growing-degree day (GDD) accumulation for each temperature increment was calculated based on daily mean temperature for that Petri dish. Two indices were obtained from a logistic growth curve used to elucidate seed germination by cultivar: (1) maximum indices of germination and (2) GDD value at 80% germination (Germ80), an indication of seed vigor the lower the Germ80 value, the greater the seed lot vigor. Based on the two indices, seed lots “AT 3081R”, “AP-3”, “GA-06G”, and “Carver” had the strongest seed vigor (Germ80 26 to 47 GDD) and a high maximum incidence of germination rate (80 to 94%). Seed lots of “C99-R”, “Georgia-01R”, “Georgia-02C”, and “Georgia-03L” had inconsistent seed performance, failing to achieve 80% germination in at least two of three years.

Use of genetically modified cultivars resistant to the herbicide glyphosate (N-phosphonomethylglycine) is strongly associated with conservation-tillage (CsT) management for maize ( Zea mays L.), soybean ( Glycine max L.), and cotton ( Gossypium hirsutum L.) cultivation. Due to the emergence of glyphosate-resistant weed biotypes, alternate weed management practices are needed to sustain CsT use. This work focused on metolachlor use (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) in a CsT system. The fate and efficacy of granular and emulsifiable concentrate (EC) formulations or an EC surrogate were compared for CsT cotton production in the Atlantic Coastal Plain region of southern Georgia (USA). The granular formulation, a clay-alginate polymer, was produced in the authors' laboratory; EC was a commercial product. In field and laboratory dissipations the granular metolachlor exhibited 8-fold greater soil persistence. Rainfall simulation runoff assessments indicated that use of the granular formulation in a common CsT system, strip-tillage (ST), may reduce metolachlor runoff loss when compared to conventional tillage (CT) management or when EC formulations are used in the ST system. Metolachlor leaching assessments using field-deployed lysimeters showed some tillage (STCT) and formulation (ECgranular) differences. Overall leaching was generally small when compared to runoff loss. Finally, greenhouse bioassays showed control of two weed species with the granular was greater than or equal to that of the EC formulation; however, the granular formulation suppressed cotton growth to a greater extent. In sum, this metolachlor granular formulation has advantages for CsT cotton production; however, additional research is needed to assess impacts on crop injury.

The herbicide glyphosate became widely used in the United States and other parts of the world after the commercialization of glyphosate-resistant crops. These crops have constitutive overexpression of a glyphosate-insensitive form of the herbicide target site gene, 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS ). Increased use of glyphosate over multiple years imposes selective genetic pressure on weed populations. We investigated recently discovered glyphosate-resistant Amaranthus palmeri populations from Georgia, in comparison with normally sensitive populations. EPSPS enzyme activity from resistant and susceptible plants was equally inhibited by glyphosate, which led us to use quantitative PCR to measure relative copy numbers of the EPSPS gene. Genomes of resistant plants contained from 5-fold to more than 160-fold more copies of the EPSPS gene than did genomes of susceptible plants. Quantitative RT-PCR on cDNA revealed that EPSPS expression was positively correlated with genomic EPSPS relative copy number. Immunoblot analyses showed that increased EPSPS protein level also correlated with EPSPS genomic copy number. EPSPS gene amplification was heritable, correlated with resistance in pseudo-F 2 populations, and is proposed to be the molecular basis of glyphosate resistance. FISH revealed that EPSPS genes were present on every chromosome and, therefore, gene amplification was likely not caused by unequal chromosome crossing over. This occurrence of gene amplification as an herbicide resistance mechanism in a naturally occurring weed population is particularly significant because it could threaten the sustainable use of glyphosate-resistant crop technology.

The development of dicamba-resistant cotton and soybean cultivars has created great concern about the potential off-target movement of dicamba 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 dicamba rates 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. Location by rate (P < 0.0002) and location by treatment timing (P < 0.004) interactions were significant. As dicamba rate increased peanut injury and yield loss increased. There was variation in peanut response by location after PRE treatments. Plains peanut was injured less among locations, possibly due to the Greenville soil there having higher organic matter and clay contents at 3.8 and 30%, resp...

Pesticide runoff research relies heavily on rainfall simulation experiments. Most are conducted at a constant intensity, i.e., at a fixed rainfall rate; however, large differences in natural rainfall intensity is common. To assess implications we quantified runoff of two herbicides, fluometuron and pendimethalin, and applied preemergence after planting cotton on Tifton loamy sand. Rainfall at constant and variable intensity patterns representative of late spring thunderstorms in the Atlantic Coastal Plain region of Georgia (USA) were simulated on 6-m2 plots under strip- (ST) and conventional-tillage (CT) management. The variable pattern produced significantly higher runoff rates of both compounds from CT but not ST plots. However, on an event-basis, runoff totals (% applied) were not significantly different, with one exception: fluometuron runoff from CT plots. There was about 25% more fluometuron runoff with the variable versus the constant intensity pattern (P = 0.10). Study results suggest that conduct of simulations using variable intensity storm patterns may provide more representative rainfall simulation-based estimates of pesticide runoff and that the greatest impacts will be observed with CT. The study also found significantly more fluometuron in runoff from ST than CT plots. Further work is needed to determine whether this behavior may be generalized to other active ingredients with similar properties [low K(oc) (organic carbon partition coefficient) approximately 100 mL g(-1); high water solubility approximately 100 mg L(-1)]. If so, it should be considered when making tillage-specific herbicide recommendations to reduce runoff potential.

Sugar beet (Beta vulgaris L.) is not currently a commercial crop in Georgia, but experimental plantings as a winter rotational crop are promising in terms of yield and industrial sugar production (T. Brenneman, personal communication). A disease outbreak of suspected bacterial origin occurred in sugar beet plots (experimental lines Beta Seed energy beet ‘BTS ENC115,’ ‘BTS EGC184,’ ‘BTS EGC195,’ and ‘BTS 1EN6702’) in Tift Co., GA, in December 2012, at ~35% incidence. Foliar symptoms included circular to irregular spots, each with a tan center and dark margin. Ten leaves/experimental line with leaf spot symptoms were collected, and bacterial isolations made on King's B agar medium. After 48 h of incubation, cream-colored, fluorescent yellow, round colonies with smooth margins were isolated. The isolates were each gram negative, oxidase negative, non-pectolytic on potato, arginine dihydrolase negative, produced levan, and gave a hypersensitivity response (HR) on tobacco. These characteristics indicated that the isolates belonged to Pseudomonas syringae van Hall LOPAT group Ia (3). The 16S-23S rRNA (internal transcribed regions) (1) from four foliar isolates (SB-1, SB-2, SB-3, and SB-4), one/experimental line, was amplified, and the resultant PCR products were sequenced and BLAST searched in GenBank. The 16S-23S rRNA sequences matched those of P. syringae pv. syingae (Pss) (KF023189) and P. syringae pv. aptata (Psa) (AY342167.1) with 96 to 98% and 97 to 99% sequence identity, respectively. Also, the percent similarity of the 16S-23S rRNA sequences among the four isolates was >99% (KJ922021 to 24 for SB-1 to SB-4, respectively). The four test isolates also had ≤89 and ≤99% similarity with Pss and Psa, respectively, when tested with BIOLOG (Hayward, CA). In addition, four sugarbeet isolates along with a type strain of Psa (NCPPB 3539) were amplified using a PCR primer pair that detected the presence of the avrPphE gene, an avirulence gene present in Psa but absent in Pss (2). The type strain of Pss (NCPPB 1770) was not amplified using this primer pair. BOX-PCR analysis gave identical banding patterns for the four isolates as that of a type strain of Psa. In two independent experiments, 3-week-old seedlings of the sugar beet cv. Beta EGR099 (n = 10 seedlings/isolate/experiment) were spray-inoculated with a sterilized water suspension of 1 × 108 CFU/ml of each of the isolates. All of the inoculated seedlings developed symptoms (water-soaked lesions that developed into necrotic spots) 10 days after inoculation (DAI) in greenhouse conditions (~30°C and ~80% RH). All of the seedlings inoculated with the type strain of Psa also produced typical bacterial blight symptoms at 10 DAI. In contrast, five control seedlings inoculated with sterilized water remained asymptomatic, and target bacterial colonies were not re-isolated from the leaves of these plants. Bacterial colonies were re-isolated from symptomatic seedlings, and showed similar characteristics based on physiological tests, BIOLOG profile, BOX-PCR analysis, and positive amplification with the avrPphE PCR assay, which indicated that these strains were Psa. To our knowledge, this is the first report of Psa in sugarbeet in Georgia. The fact that a Psa strain was also isolated from a sugar beet seed lot (data not shown) suggested that the pathogen may have been introduced on contaminated seeds. Knowledge of the presence of Psa in the agro-ecosystem of Georgia may encourage scientists to implement integrated management practices for this pathogen. References: (1) C. Guasp et al. Int. J. Syst. Evol. Microbiol. 50:1629, 2000. (2) Y. Inoue and Y. Takikawa. Page 687 in: Presentations 6th Int. Conf. Pseudomonas syringae Pathovars and Related Pathogens, 2003. (3) R. A. Lelliot et al. J. Appl. Bacteriol. 29:470, 1966.

Yellow bud, an emerging bacterial disease of onion ( Allium cepa ), has been spreading throughout the Vidalia onion-growing region in Georgia, USA since 2007 (Gitaitis, 2012). Symptoms of yellow bud include intense chlorosis in emerging…