Replacement studies were conducted under greenhouse conditions to determine if available soil water influences the competitive interaction between soybean and Florida beggarweed. Stomatal conductance and leaf water potential were determined for both species under different levels of available soil water to identify possible mechanisms involved in changes in the relative competitiveness induced by the water deficits. Soybean leaf area and aboveground biomass were greater than for Florida beggarweed under optimum water, but equal to or less than Florida beggarweed with water stress. Soybean was more competitive than Florida beggarweed when there was adequate soil water but less competitive than Florida beggarweed under water stress. Stomatal conductance was higher for soybean with optimum soil water (at high leaf water potentials) but equal to Florida beggarweed as soil water became limiting (low leaf water potentials). These data indicated that water stress differentially affected soybean and Florida beggarweed.

Field evaluations were made on the effects of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} on Florida beggarweed [Desmodium tortuosum (SW) DC. # DEDTO] and sicklepod (Cassia obtusifolia L. # CASOB) control in peanuts (Arachis hypogaea L.). Crop yield was reduced at 392 and 504 g ae/ha and with preemergence applications. Florida beggarweed control was not achieved with this herbicide. Maximum sicklepod control (approximately 80%) was achieved with 392 and 504 g/ha applied postemergence. In a separate study, several herbicide systems utilizing imazaquin were compared to a standard weed control program. All these systems provided weed control and yields that were comparable to the standard weed control system; thus the inclusion of imazaquin offered no advantage over the standard system.

The response of peanut to low rates of MSMA under weed-free conditions was studied in 1992 and 1994 near Tifton, GA. MSMA was applied 40, 70, 100, or 130 days after emergence (DAE). At each application timing, MSMA was applied at 0, 90, 168, and 336 g ai ha−1. MSMA application timing did not affect peanut yield. Increasing rates of MSMA caused minor reduction in peanut yield. Analysis using atomic absorption spectroscopy showed elemental arsenic accumulation of ≤ 0.7 ppm in peanut kernels from MSMA applied 70 and 100 DAE. This approximates the time interval of peanut pod and kernel formation. MSMA applied 40 and 130 DAE resulted in little detectable arsenic in kernels. Low rates of MSMA, originating as drift from aerial applications to cotton or illegal and unsound applications to peanut for Florida beggarweed control, are not likely to reduce peanut yields. The greatest hazard from peanut exposure to MSMA is accumulation of arsenic in kernels, which would adversely affect peanut marketability and consumer demand.

Greenhouse and growth chamber studies were conducted to determine conditions for infection of the fungal pathogen Colletotrichum truncatum (Schw.) Andrus and Moore on Florida beggarweed (Desmodium tortuosum (Sw.) DC. # DEDTO and to determine the host specificity of this fungus. Optimum conditions for disease development were 14 to 16 h incubation in 100% relative humidity (RH) at 24 to 29 C. Control of Florida beggarweed with 105 to 107C. truncatum spores/ml was greatest in the cotyledon stage and decreased with plant age. Ten of 18 Desmodium species tested were susceptible to the Florida beggarweed isolate of C. truncatum but 13 other plant species and varieties were resistant and 61 were immune.

Greenhouse and field studies demonstrated that naptalam reduced paraquat activity by as much as 30% on sicklepod, smallflower morningglory, Florida beggarweed, and peanut Sequential application experiments, i.e. naptalam applied 2 or 24 h prior to an application of paraquat, as well as absorption studies utilizing 14C-paraquat, indicated that the antagonism was due largely to reduced paraquat absorption. Scanning electron microscopy revealed that application of naptalam, as well as naptalam applied with paraquat, resulted in amorphous deposits on the leaf surface which may account for the antagonism.

Postemergence treatments utilizing various combinations of fluazifop-P, paraquat, and 2,4-DB were compared to a preplant-incorporated (PPI) application of benefin followed by a ground-cracking application of alachlor and dinoseb plus naptalam and a postemergence application of 2,4-DB for weed control, peanut yield, and net economic return to land, overhead, and management. The greatest peanut yields (3-yr average of 4510 kg/ha) and net returns (3-yr average of $521/ha) were provided by a postemergence system that utilized one ground-cracking and one postemergence application of paraquat and one postemergence application of fluazifop-P and 2,4-DB. Seven postemergence systems provided equivalent or greater yield and net returns than the PPI and dinoseb plus naptalam system. Fresh weight reductions of Texas panicum, sicklepod, Florida beggarweed, and pitted morningglory from postemergence weed control systems were equivalent to reductions obtained from the PPI and dinoseb plus naptalam system. The addition of paraquat and 2,4-DB to the PPI and dinoseb plus naptalam system improved the 3-yr average peanut yield and net economic return by 510 kg/ha and $136/ha, respectively, compared to the same system without paraquat and 2,4-DB.

Absorption of foliar-applied 14C-imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} 72 h after treatment was higher than 90% for soybean [Glycine max (L.) Merr. ‘Braxton’], peanut (Arachis hypogaea L. ‘Florunner’), common cocklebur (Xanthium strumarium L. # XANST), sicklepod (Cassia obtusifolia L. # CASOB), and Florida beggarweed [Desmodium tortuosum (SW.) # DEDTO]. Both symplasmic and apoplasmic translocation of the herbicide were evident. Imazaquin half-life was 4.4 days in soybean, 5.3 days in peanut, 9.6 days in Florida beggarweed, 12.7 days in sicklepod, and 39.8 days in cocklebur. Tolerance of these species to foliar-applied imazaquin as determined in greenhouse studies with 21-day-old seedlings was as follows: soybean = peanut > Florida beggarweed > sicklepod > cocklebur. Tolerance was directly correlated to imazaquin halflife within the tissue of the respective species.

Mixtures of chlorimuron and 2,4-DB were additive with respect to crop injury and were either additive or slightly antagonistic with respect to weed control in greenhouse experiments. Absorption and translocation of 14C following application of 14C-chlorimuron and 14C-2,4-DB were not affected by the presence of the other unlabeled herbicide, except in Florida beggarweed and peanut where 2,4-DB affected distribution of 14C-chlorimuron in the treated leaf. In field studies, maximum efficacy was obtained with mixtures of chlorimuron plus 2,4-DB applied 7 or 9 wk after planting. Florida beggarweed control was greatest with chlorimuron or chlorimuron mixtures while the addition of 2,4-DB to chlorimuron improved morningglory and sicklepod control. At 9 and 11 wk after planting, addition of 2,4-DB to chlorimuron controlled Florida beggarweed better than chlorimuron alone. Peanut yields were increased by the addition of 2,4-DB at later applications.

Bentazon reduced paraquat phytotoxicity to Texas panicum, sicklepod, Florida beggarweed, and peanut. Bentazon applied alone had minimal effect on these species. Smallflower morningglory was more sensitive to bentazon than to paraquat; the interaction of paraquat and bentazon varied from antagonistic to synergistic depending upon the specific combination of rates. Antagonism with tank-mixed combinations was also obtained by applying bentazon prior to paraquat, but not with the reverse. Studies with 14C-labeled herbicides revealed that each herbicide inhibited foliar penetration of the other. In field studies, adding bentazon to paraquat reduced crop injury. However, except for smallflower morningglory, weed control was also reduced.

Field experiments conducted at three locations in Georgia during 1991 and 1992 evaluated AC 263,222 and imazethapyr rates alone at 18, 36, 54, or 72 g ai/ha and in mixture for a total of 36, 54, or 72 g/ha of herbicide applied early-POST for weed control, peanut injury, and yield. An application of AC 263,222 at 72 g/ha controlled (> 90%) Ipomoea morningglories, sicklepod, smallflower morningglory, and yellow nutsedge in all experiments and coffee senna and Florida beggarweed at Chula in 1991. Bristly starbur was controlled at least 90% with AC 263,222 at 72 g/ha at Tifton in 1991, but less than 62% at Chula in 1991. Imazethapyr applied at 72 g/ha controlled coffee senna, Ipomoea morningglories, and smallflower morningglory at least 85%, but did not control Florida beggarweed or sicklepod and provided inconsistent bristly starbur and yellow nutsedge control. Bristly starbur and yellow nutsedge control was increased with several AC 263,222 plus imazethapyr mixtures. High peanut yields comparable to the standard were indicative of the AC 263,222 rate applied whether alone or in mixture with imazethapyr.

Florida beggarweed germination in laboratory experiments was highest between 21 and 38 C and at osmotic potentials above −0.2 MPa, with complete germination inhibition below −0.8 MPa. Patterns of seedling emergence in the field corresponded to timing and size of rainfall events in relation to the time of soil disturbance. Smaller percentage total seasonal emergence was observed following large rainfall events where soil had not been disturbed compared with plots recently disturbed, and soil disturbance not followed by rainfall did not promote major weed flushes.

In the greenhouse, naptalam at 1.1 to 4.5 kg ai ha−1 antagonized activity of paraquat at 0.04 to 0.14 kg ai ha−1 in 14 of 16 rate combinations when applied to sicklepod. Sicklepod shoot fresh weight reduction was less compared to that obtained with paraquat alone when paraquat at 0.04 kg ha−1 was mixed with bentazon at 0.42 to 0.84 kg ai ha−1 or monocarbamide dihydrogensulfate at 14 to 58 kg ai ha−1. Paraquat activity on Florida beggarweed was antagonized by mixtures of paraquat at 0.04 or 0.07 kg ha−1 with bentazon at 0.63 or 0.84 kg ha−1 or paraquat at 0.04 to 0.14 kg ha−1 with naptalam at 3.4 or 4.5 kg ha−1. Mixtures of lactofen at 0.06 to 0.22 kg ai ha−1 with monocarbamide dihydrogensulfate at 14 kg ha−1 or lactofen at 0.06 or 0.16 kg ha−1 with alachlor at 1.4 to 2.8 kg ai ha−1 synergistically increased tall morningglory shoot fresh weight reduction. In the field, excellent sicklepod shoot fresh weight reduction by paraquat applied alone masked most antagonistic effects of paraquat mixtures. Addition of alachlor to monocarbamide dihydrogensulfate at 29 kg ha−1 improved activity on sicklepod compared to monocarbamide dihydrogensulfate applied alone.

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

Field studies were conducted from 1991 through 1993 to compare Weed control, peanut tolerance, yield, and net return from imazethapyr applied alone or in combination with paraquat. Sicklepod and Florida beggarweed were controlled with paraquat early POST followed by a POST application of either paraquat with 2,4-DB or paraquat with 2,4-DB and bentazon. Imazethapyr-based early POST treatments offered no improvement. An early POST application of paraquat with bentazon or imazethapyr was required for maximum control of bristly starbur. Imazethapyr applied alone early POST, with no further treatment, provided optimum yellow nutsedge control. Maximum yield and net return were associated with any paraquat-containing early POST-applied treatment followed by one of the tank mixed POST options.

Field studies conducted at six locations in Georgia and one location in Virginia evaluated imazethapyr and imazethapyr mixtures for weed control, crop tolerance, and peanut yield. Imazethapyr applied early postemergence controlled bristly starbur, coffee senna, common cocklebur, Ipomoea species, jimsonweed, prickly sida, and smallflower morningglory at least 91% and controlled yellow and purple nutsedge 88 and 98%, respectively. Paraquat plus bentazon applied early postemergence did not control the aforementioned weeds as well as imazethapyr or imazethapyr mixtures. Paraquat applied with imazethapyr reduced bristly starbur control 15% compared to imazethapyr alone but did not influence control of the other species. Imazethapyr control of bristly starbur was not improved by the addition of bentazon. Sicklepod control was less than 24% with imazethapyr and was at least 58% with imazethapyr plus paraquat Imazethapyr plus paraquat controlled sicklepod better than paraquat plus bentazon at three of the four locations evaluated. Imazethapyr did not control Florida beggarweed, while imazethapyr plus paraquat controlled at least 53%. Peanut injury was minimal 30 d after application for all treatments.

Field experiments were conducted in 1982 and 1983 on a Dothan sandy loam (Plinthic Paleudult) at Headland, AL, to investigate minimum-tillage production of peanuts (Arachis hypogaea L.). The experiments included two peanut varieties: a) ‘Pronto’ (an earlier maturing Spanish type), and b) ‘Florunner’ (a later maturing runner type). Two row-spacing patterns were used: a) conventional 91-cm rows, and b) a modified twin 18-cm row pattern. A constant seeding rate (140 kg/ha) was used regardless of row spacing. Six herbicide systems were evaluated within each combination of variety and row spacing. The Florunner variety outyielded the Pronto variety across both years and weed management systems. Modified twin 18-cm rows outyielded conventional 91-cm rows across years and peanut varieties. Two of the six weed management systems were successful: 1) paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) + oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) (preemergence), paraquat (ground cracking), naptalam (N-1-naphthylphthalamic acid) + dinoseb (2-sec-butyl-4,6-dinitrophenol) (postemergence); and 2) paraquat + pendimethalin [N-(1-ethylpropyl-3,4-dimethyl-2,6-dinitrobenzenamine] (preemergence), acetochlor [2-chloro-N(ethoxymethyl)-6’-ethyl-o-acetotoluidide] + dinoseb (ground cracking), and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl]amino]-2-methylpropionitrile} (early postdirected spray). Both systems provided the best overall control of Texas panicum (Panicum texanum Buckl. ♯ PANTE), Florida beggarweed [Desmodium tortuosum (Sw.) DC. ♯ DEDTO], and sicklepod (Cassia obtusifolia L. ♯ CASOB) and were acceptable for use in minimum-tillage peanut production.

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

Tolerance of species to foliar applications of the ethyl ester of chlorimuron as determined in greenhouse studies with 21-day-old seedlings was: soybean = peanut > prickly sida > sicklepod > Florida beggarweed > common cocklebur. Absorption of foliar-applied 14C-chlorimuron 72 h after application was similar in soybean, peanut, sicklepod, common cocklebur, and prickly sida, but much less in Florida beggarweed. Slight symplasmic and apoplasmic translocation of the herbicide was evident in all species. Metabolism of chlorimuron 72 h after application was greatest in soybean and least in common cocklebur. Species tolerance to chlorimuron was directly correlated (r2 = 0.93) to the amount of unmetabolized chlorimuron (dpm/g dry wt) in the plant. Peanut exhibited increased tolerance to chlorimuron with age; this result was attributed to reduced absorption and translocation and more extensive metabolism of the absorbed herbicide by older plants.

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%, and Ipomoea morningglory 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.

Field experiments were conducted at Jay and Marianna, FL in 1988 and 1989 to determine the effects of sicklepod, Florida beggarweed, and common cocklebur density on chlorothalonil deposition to peanut foliage, peanut foliar disease incidence, and peanut yield. At a density of four weed plants per 8 m of row, Florida beggarweed and sicklepod reduced chlorothalonil deposition on peanut foliage by 20%, while common cocklebur reduced fungicide deposition by 34%. At the same density, incidence of the foliar diseases early leaf spot and late leaf spot increased 10% with Florida beggarweed, 14% with sicklepod, and 20% with common cocklebur compared with weed-free peanut. The predicted peanut yield loss from a weed density of four plants per 8 m was 16 to 19% for Florida beggarweed, 23 to 25% for sicklepod, and 31 to 39% for common cocklebur. Weed biomass increased with increasing weed density.