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  • Author or Editor: James P. Gilreath x
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Abstract

Postemergence applications of fluazifop-butyl and sethoxydim at rates of 0.28, 0.56, and 0.84 kg a.i./ha provided excellent control of seedling Digitarla ciliaris (Retz.) Koel and Eleusine indica (L.) Gaertn. in achimenes (Achimenes grandiflora Dc. ‘Cascade Violet Night’), impatiens (Impatiens wallerana Hook. f. ‘Elfin Salmon’), marigold (Tagetes erecta L. ‘Yellow Galore’), petunia (Petunia hybrida Hort. Vilm.-Andr. ‘Burgundy’), and salvia (Salvia splendens F. Sellow ex Roem. & Schult. ‘Blaze of Fire’). Herbicide treatment did not affect achimenes rhizome size or weight nor plant vigor, height, or bloom production of impatiens, marigolds, petunias, or salvia. Chemical names used: (±)–2[4–[[5–(trifluoromethyl)2–pyridinyl]oxy]phenoxy]propanoic acid (fluazifop-butyl); 2-[1](ethoxyimino)butyl]propyl]-3-hydroxy-2-cyclohexenl-1-one (sethoxydim).

Open Access

Abstract

Preemergence herbicides for weed control in field-grown statice [Limonium sinuatum (L.) Mill.], applied pretransplant, with a second posttransplant application over the top of the crop before flowering, were evaluated. DCPA, oxadiazon, and oxyfluorfen generally provided safe, efficacious weed control in the first experiment (1984) and were further evaluated in the second experiment (1985), wherein crop vigor and yield were not reduced. Control of most weeds was good with DCPA, oxadiazon, and oxyfluorfen; however, crabgrass [Digitaria sanguinalis (L.) Scop.] control with oxyfluorfen was inconsistent in both experiments and decreased late in the season. Chemical names used: dimethyl 2,3,5,6-tetrachloro-1,4-benzene-dicarboxylate (DCPA); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene (oxyfluorfen).

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A 2-year field study was conducted in two locations in the Dominican Republic to determine the influence of various support systems and nitrogen fertilization programs on passion fruit (Passiflora edulis var. flavicarpa) yield and economic returns. Three trellis systems were used: 1) single line, where a single wire was placed along the planting rows at 2 m high; 2) double lines, where two wires were established along the planting rows at 2 and 1 m high, respectively; and 3) crossed lines, with wires at 2 m high, allowing the vines to grow both along and across the planting rows. Nitrogen (N) fertilization rates were 13, 26, and 52 g/plant of N every 20 days. Plants trained with the single- and double-line support systems combined with 52 g/plant of N had higher marketable yield and had the lowest proportion of non-marketable fruit/plant per year. Partial budget analysis indicated that the single-line support system had a marginal return rate of 36% compared to the double-line support system.

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Over the years, efficacy of metam potassium (MK) on purple nutsedge (Cyperus rotundus) control has been inconsistent, in many cases because of a lack of knowledge about application techniques. Therefore, field studies were conducted to determine the effect of water delivery volumes and flow rates on purple nutsedge control with MK, and the influence of MK rates and concentrations on purple nutsedge control. Three separate studies were established for 1) water application volumes and flow rates, 2) MK application rates and concentrations, and 3) MK concentration levels. For the water application volumes and flow rate trials, a single MK rate of 60 gal/acre was injected with either 1 or 2 acre-inch/acre (27,154 or 54,308 gal/acre) of water. The water flow rates were 0.30, 0.45, and 0.60 gal/100 ft of row per minute within each water volume. An nontreated control was included. In the application rate and concentrations studies, treatments were a nontreated control, 30 gal/acre applied with 0.5 acre-inch/acre of water (≈3000 ppm), 60 gal/acre applied with either 0.5 or 1 acre-inch/acre of water (≈6000 and 3000 ppm), 120 gal/acre applied with either 1 or 2 acre-inch/acre of water (≈6000 and 3000 ppm), and 240 gal/acre applied with 2 acre-inch/acre of water (≈6000 ppm). In the MK concentration trials, 0, 2000, 3000, 4000, 5000, and 6000 ppm were tested. Results indicated that neither water volumes nor flow rates used for MK application had a significant impact on purple nutsedge control at 10 weeks after treatment (WAT). However, there was a significant effect of the combinations of MK rates and water delivery volumes on purple nutsedge densities at 4 and 15 WAT. Similarly, MK concentrations obtained from a single application rate resulted in improved purple nutsedge control up to 10 WAT, reducing densities to less than 5 plants/ft2 with 6000 ppm of MK.

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Among the current methyl bromide alternatives under study, propylene oxide (Propozone) has shown potential to control soilborne diseases, nematodes, and weeds in polyethylene-mulched tomato. However, further research is needed to determine the appropriate application rates to control nutsedge in the crop. Also, the effect of this fumigant on tomato nutrient absorption has not been determined yet. Therefore, field trials were conducted for this purpose in Bradenton, Fla. Tested rates of Propozone were 0, 190, 380, 570, 760, and 950 L·ha–1 and were shank-applied in raised planting beds three weeks before `Florida 47' tomato transplanting. Examined data indicated that there was a rapid decrease in nutsedge density with 570 L·ha–1. For phosphorus (P) and potassium (K) foliar content, there was a linear increase of P concentrations as rate increase, whereas K content increased rapidly after 190 L·ha–1. The highest tomato yields were obtained with 760 and 950 L·ha–1 of Propozone.

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Purple nutsedge can easily penetrate polyethylene mulch films. However, there are no reports on possible differences among mulch films. Because of this situation, field trials were conducted in Ruskin and Bradenton, Fla., during 2002 and 2003. In Spring 2002, the treatments were a) no mulch, b) black Pliant High Barrier mulch, and c) green Klerk's Virtually Impermeable Film (VIF). In Spring 2002, the films were a) black Pliant High Barrier, b) black IPM Bromostop, c) metallized Pliant, and d) green Klerk's VIF. The number of nutsedge emerged through the films was determined. No fumigants or herbicides were applied. Results indicated that the Klerk's VIF had the lowest nutsedge densities. No nutsedge control differences were found between the IPM Bromostop and the metallized Pliant films. These differences might be due to the physical properties of the films, including stretching and thickness.

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Two independent field studies were conducted to determine the efficacy of methyl iodide (MI) formulations and rates on mixed nutsedge [purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus)] stands and their effects on tomato (Solanum lycopersicum) yields. In both studies, treatments were rates of two formulations of MI + chloropicrin (Pic) at the 98:2 (v/v) and 50:50 (v/v) proportions. In the MI + Pic 98:2 study, the fumigant rates were 0, 100, 125, 150, 175, and 200 lb/acre in Spring 2004 and 0, 125, 150, 175, and 200 lb/acre in Fall 2004. In the MI + Pic 50:50 study, the rates were 0, 200, 250, 300, 350, and 400 lb/acre during both seasons. Additionally, a grower standard was included in each study, which consisted of plots fumigated with methyl bromide (MBr) + Pic 67:33 (v/v) at a rate of 350 lb/acre. Higher rates of MI + Pic 98:2 and 50:50 significantly reduced mixed nutsedge densities and increased relative marketable fruit weight of tomato. Plots fumigated with MBr + Pic were weed-free at the sampling times during both studies. Data from both studies indicated that MI + Pic 98:2 and 50:50 rates of 125 and 200 lb/acre, respectively, consistently provided the highest marketable fruit weights and mixed nutsedge control, which were similar to those obtained in plots treated with MBr + Pic.

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Field trials were conducted from 1999 to 2003 to determine whether chloropicrin (Pic) stimulates nutsedge (Cyperus spp.) emergence through polyethylene mulch, and to examine at which Pic rate the stimulatory effect is maximized. Shank-injected Pic rates were 0, 50, 100, 150, 200, and 250 lb/acre. Application rates between 107 and 184 lb/acre of Pic stimulated nutsedge sprouting through polyethylene mulch by 60%, 400%, 58%, and 120% more than the nontreated control during four of the seasons. Rates above 250 lb/acre eliminated the stimulatory effect on nutsedge, reducing densities to the same levels as the nontreated control. The exact physiological mechanism of this stimulation is still unknown.

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Two field trials were conducted to determine the effect of reduced methyl bromide plus chloropicrin (MBr + Pic 67:33 v/v) rates applied under two types of virtually impermeable films (VIF) on nutsedges (Cyperus spp.) and stunt nematode (Tylenchorhynchus spp.) control, and bell pepper (Capsicum annuum) crop yield. A split-plot design with six replications was established, with MBr + Pic rates in the main plots and mulch types as subplots. MBr + Pic rates were 0, 88, 175, and 350 lb/acre. Mulch types were low-density polyethylene (LDPE) mulch, Hytibar VIF, and Bromostop VIF. Results showed that there were no differences on weed and nematode control, and bell pepper fruit yield between the two types of VIF. Two exponential models characterized the nutsedge responses to MBr + Pic rates with LDPE mulch and VIF, with weed densities declining as MBr + Pic rates increased. Reducing MBr + Pic rates by one-half (175 lb/acre) under VIF provided similar nutsedge control as the full-rate (350 lb/acre) with LDPE mulch. Similar results were observed with stunt nematode, where the most effective control occurred with VIF. Bell pepper yield with LDPE mulch responded linearly to increased MBr + Pic rates. However, a logarithmic model described the response of pepper yields to the fumigant rates under VIF. The application rate of this fumigant could be effectively reduced to 25% of the commercial rate (350 lb/acre) under either VIF, without causing significant bell pepper yield losses.

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Although methyl bromide (MBr) has been phased out in developed countries, limited amounts will still be available in the United States for the next few years through critical-use exemptions. Therefore, production practices reducing MBr use are desirable from the grower and environmental standpoints. Fumigation efficacy depends on the duration of fumigants in the soil and mulch permeability; thus, field trials were conducted to compare MBr retention of low- and high-density polyethylene (LDPE and HDPE respectively) mulches with seven metallized mulches and virtually impermeable films (VIF) from different manufacturers, and to assess the effect of MBr retention on nutsedge (Cyperus rotundus and C. esculentus) control with these mulches. The compared mulches were 1) white VIF; 2) black VIF; 3) white-on-black VIF; 4) cowound VIF, which has a clear nylon layer that covers the bed and is superimposed with a layer of black HDPE mulch; 5) metallized; 6) metallized heat trap with a black stripe on the bed center; 7) metallized with a black stripe on the bed center; 8) black LDPE mulch; and 9) black HDPE mulch. All treatments received 175 lb/acre of MBr + chloropicrin (Pic; 67:33 v/v). A nonfumigated control plot covered with LDPE mulch, and a treatment covered with HDPE mulch and fumigated with 350 lb/acre of MBr + Pic were also established. Nutsedge emergence through mulches increased rapidly beginning 18 days after treatment (DAT). Nutsedge populations at 28 DAT in the nonfumigated control covered with LDPE mulch had the greatest emergence (88.8 plants/ft2), followed by LDPE and HDPE mulches with 175 lb/acre of MBr + Pic (67.0 plants/ft2), HDPE mulch with 350 lb/acre of MBr + Pic (25.0 plants/ft2), and VIF and metallized mulches with 175 lb/acre of MBr + Pic (<2 plants/ft2). There were no significant differences in fumigant retention between the metallized mulches and VIF. These mulches retained 3.7 and 1.8 times more MBr than HDPE and LDPE mulches fumigated with 175 and 350 lb/acre of MBr + Pic, respectively.

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