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Shiv D. Sharma and M. Singh

Various combinations of glyphosate and 2,4-D (± surfactant) were evaluated for control of Brazil pusley [Richardia brasiliensis (Moq.) Gomez]. Typical 2,4-D symptoms on plants were manifested within 2 to 3 days after treatment. Application of glyphosate alone had only marginal effects (14%) on Brazil pusley, but the addition of Induce® (nonionic surfactant) significantly increased control to 83% and reduced the fresh weight by 68%. Application of Landmaster®II or a tank-mix of glyphosate + 2,4-D (± surfactants) resulted in 96% to 100% control. Treatment with 2,4-D alone, or with Induce®, or L-77® (organosilicone surfactant) resulted in 84%, 90%, or 100% control, respectively. Very low fresh weights of Brazil pusley were recorded when 2,4-D +Induce® or L-77®, Landmaster®II (± surfactants), or the tank-mix (± surfactants) were applied. In the regrowth studies, shoot weight was greater following application of glyphosate with or without L-77® or Kinetic® (a blend of nonionic and organosilicone) than following other treatments. The fresh weight of the shoots in the regrowth study, recorded following the application of 2,4-D or Landmaster®II (± surfactants), was very low except when Kinetic® was added to Landmaster®II. No regrowth of shoots occurred following the tank-mix treatment. Similar observations were recorded for roots. Plants treated with 2,4-D did not regrow. The presence of 2,4-D in either formulation accelerated synergistic effect of the glyphosate to the target site. Therefore, 2,4-D could be used either as a component of a formulation or in a tank-mix with glyphosate to control Brazil pusley. Chemical names used: N-(phosphonomethyl glycine) (glyphosate); 2,4-dicholorophenoxyacetic acid (2,4-D).

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S.D. Sharma and M. Singh

Greenhouse and field trials were carried out to evaluate carfentrazone as a potential tank mix with glyphosate to control weeds. Application of active ingredient glyphosate at 1.15 kg·ha−1 provided 44%, 50%, 19%, and 17% control of ivyleaf morning-glory, milkweed vine, hemp sesbania, and field-bind weed (stage 1), respectively, and increased to 45%, 51%, 31%, and 76%, respectively, with active ingredient of 2.30 kg·ha−1. Carfentrazone as active ingredient at 17.7 g·ha−1 achieved 53%, 90%, and 99% control of hemp sesbania, ivyleaf morning-glory, and milkweed vine (stage 1), and increased to 88%, 98% in first two weed plants, respectively, with active ingredient at 52.2 g·ha−1. Either rate of carfentrazone at any stages of field-bind weed yielded ≈100% control. Application of tank-mixed glyphosate and carfentrazone to ivyleaf morning-glory and hemp sesbania (stage 1) demonstrated greater control than their sole applications. A complete control of milkweed vine and field-bind weed (stage 1) was achieved by tank-mixed glyphosate and carfentrazone. Corresponding to percent control values a reduction in biomass value was also recorded. Biomass reduction with glyphosate at either stage of ivyleaf morning-glory was only 14%–24% and reduction with carfentrazone was 40%–47%. Biomass was further reduced with the tank-mixed glyphosate and carfentrazone. A similarly trend in biomass reduction was noted in milkweed vine and hemp sesbania. However, ivyleaf morning-glory was found to be the most tolerant weed to glyphosate followed by hemp sesbania, milkweed vine, and field-bind weed. Tank-mixed applications of these two herbicides further increased the percent control and biomass reduction. In all weed species, there was a significant decrease in percent biomass reduction with age. Although the types of weed were different in the field experiment and greenhouse, a similar trend was observed in the percent control achieved with glyphosate, carfentrazone, and their tank-mixed application. Tank-mixed applications achieved 93%–95% control of Brazil pusley and 75%–83% control of passion flower. These values were significantly higher than the percent control achieved with application of only glyphosate. Therefore, tank-mixed application of glyphosate and carfentrazone may be beneficial than sole application to control broadleaf weeds.

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B.P. Singh and U.M. Sainju

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Upendra M. Sainju, Syed Rahman and Bharat P. Singh

The ability of hairy vetch (Vicia villosa Roth) residue (100 g/plant) to supply N and to increase yields of tomato (Lycopersicon esculentum Mill.) was compared with that of N fertilization (0, 4.1, and 8.2 g/plant N) in a medium containing a mixture of 3 perlite: 1 vermiculite in a greenhouse and a lathhouse. Hairy vetch residue did not interact with N fertilization in affecting tomato yield and medium N concentration. In the greenhouse, leaf dry weight, leaf and stem N uptake, total (fruit + stem + leaf + root) dry weight and N uptake of tomato, and NH4 + and inorganic N concentrations in the medium at transplanting were significantly greater with than without residue. In the lathhouse, fruit number, fresh and dry yields and N uptake, leaf, stem, and root dry weights and N uptake, root length, total dry weight and N uptake of tomato, and NH4 +, NO3 -, and inorganic N concentrations in the medium at transplanting, and inorganic N at harvest were greater with than without residue. Nitrogen fertilization increased fruit number, fresh and dry yields and N uptake, stem, leaf, and root dry weights and N uptake, root length, and total dry weight and N uptake. The residue was as effective in increasing fresh fruit yield, total dry weight, and N uptake as was 4.4 to 7.9 g/plant of N fertilizer. Tomato yield and N uptake per unit amount of N supplied was greater for the residue than for N fertilization, suggesting that hairy vetch residue can be effectively used as N fertilizer for tomato production.

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Bharat P. Singh, Upendra M. Sanju and Wayne F. Whitehead

Our objective was to determine the effect of winter cover crops on the yield and N concentration of the following crop of tomato. No commercial fertilizer was applied to the tomato crop. Cover crops were planted in fall in a randomized complete-block design with control (fallow), rye, hairy vetch, and crimson clover treatments. `Mountain Pride' tomato was planted in spring after incorporating cover crops into the soil. Soil inorganic N content during the tomato growing season was significantly affected by the nature of cover crops planted during winter. Tomato planted after legumes had significantly greater amounts of inorganic N available for uptake compared to nonlegume or control. A rye cover crop did not have any effect on the yield of the ensuing tomato crop. On the contrary, a 15% increase in tomato fruit yields resulted from cover cropping with legumes. The N concentration in fruit in all treatments was similar. However, tomato grown after rye had significantly lower vegetative N concentration. Total N uptake was significantly greater in tomato succeeding legumes compared to nonlegume or fallow. It was concluded that by adding inorganic N into the soil, legumes increased the fruit yield and N uptake of the succeeding tomato crop.

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E.M.K. Koinange, S.P. Singh and P. Gepts

Cultivated plants and their wild progenitors show marked phenotypic differences regarding seed dormancy, the ability to disperse seeds, growth habit, phenology, photoperiod sensitivity, etc. We have used RFLP mapping to investigate the genetic control of these differences in a recombinant inbred population derived from across between a snap bean and a wild bean. Traits were scored either at Davis or in Colombia. Our results suggest that the genetic control is relatively simple. In particular, most of the phenotypic variation (>60%) in the population could be accounted for in genetic terms for all but two traits. The genetic control of many traits involved genes with major effect (>30%). Some regions of the genome had major effects on several traits. Our results suggest that evolution can proceed by macromutations, domestication could have taken place fairly rapidly and introgression of additional genetic diversity could be itrogressed relatively easily from wild beans into the cultivated bean gene pool.

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Amit J. Jhala, Analiza H.M. Ramirez and Megh Singh

Herbicides are usually applied multiple times by growers for season long weed control in Florida citrus (Citrus sp.). Rimsulfuron, a sulfonylurea herbicide has been recently registered for control of certain grasses and broadleaf weeds in citrus. To increase the weed control spectrum and reduce application cost, citrus growers often prefer to tank mix herbicides. Field experiments were conducted in 2010 and 2011 in citrus groves in central Florida to evaluate weed control efficacy and crop safety of rimsulfuron applied alone or in tank mixes with flumioxazin, pendimethalin, or oryzalin. Herbicides were applied sequentially in spring and fall in both years on the same experimental plot. Results suggested that rimsulfuron applied alone controlled >80% broadleaf and grass weeds up to 30 days after treatment (DAT) and was comparable to tank mixing rimsulfuron with pendimethalin or oryzalin; however, control was reduced beyond 30 DAT. Rimsulfuron tank mixed with flumioxazin was the most effective treatment at 30 and 60 DAT that provided, respectively, ≥88% and >75%, control of broadleaf weeds including brazil pusley (Richardia brasiliensis), dog fennel (Eupatorium capillifolium), common ragweed (Ambrosia artemisiifolia), cotton weed (Froelichia floridana), and virginia pepperweed (Virginia virginicum) compared with other treatments. Control of natalgrass (Melinis repens) was higher in all tank mix treatments compared with rimsulfuron applied alone with no difference among tank mix partners. Rimsulfuron tank mixed with pendimethalin or oryzalin had no advantage over rimsulfuron applied alone for control of broadleaf weeds. Among sequential applications, weed control was better after fall herbicide application (August) compared with spring (April) because of residual activity of fall applied herbicides. Rimsulfuron tank mixed with flumioxazin will provide citrus growers with an additional weed control option.

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H.F. Abouziena, O.M. Hafez, I.M. El-Metwally, S.D. Sharma and M. Singh

Organic crop production, whether for export or local consumption, is increasing to avoid the residual effects of synthetic herbicides in foods, soil, and water, toxicity to other nontarget organisms, and herbicide-resistant weed populations. Organic farmers consistently ranked weed management as one of their most important production problems. Therefore, a 2-year study was conducted under 15-year-old mandarin trees to compare the effects of rice straw mulch, cattail mulch, black plastic mulch, hand hoeing, cultivation, glyphosate, and unweeded control treatments on weed control, fruit yield, and fruit quality. The greatest control (94%–100%) of weeds occurred with the plastic mulch (200 or 150 μm) and three mulch layers of rice straw or cattail. Covering soil with cattail or rice straw mulch (two layers) gave 85% to 98% control of weeds. Uncontrolled weeds in the weedy control caused significant reduction in yield and fruit quality and decreased the yield/tree by 62% compared with hand hoe treatment. Plastic mulches of 200 and 150 μm, cattail (Cyprus articulatus L.) mulch (two or three layers) and two mulch layers of rice (Oryza sativa L.) straw treatments significantly increased the fruit yield/tree by 24%, 18%, 20%, 11%, and 12% more than cultivation treatment, respectively, without significant differences among these superior treatments. Soil mulching with three layers of rice straw, cultivation, glyphosate, and 80-μm plastic mulch treatments caused a significant reduction in weed density and weed biomass, but gave lower yield than superior treatments. Total soluble solids of fruits was unaffected by any of the weed management strategies, whereas values of total acidity and vitamin C were significantly lower in the unwedded control than most weeded treatments. These results demonstrate that two layers of cattail or rice straw mulch could be used effectively for controlling weeds in citrus groves. Their effectiveness in controlling weeds may increase their use in agriculture systems with a concomitant decrease in the need for synthetic herbicides. Further studies are needed to evaluate their side effects on beneficial organisms, diseases, and insects.

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Geno A. Picchioni, Jagtar Singh, John G. Mexal and Ryan M. Goss

The authors used a simple procedure to teach how to generate evapotranspiration (ET) data for both 1- and 5-gal pots of the xeric shrub apache plume (Fallugia paradoxa) and the mesic vine japanese honeysuckle (Lonicera japonica ‘Halliana’). In-class instruction and assigned reading prepared students for collecting data over a 22-day period (12 Apr. to 3 May), processing data on an electronic spreadsheet, accessing the Internet to acquire reference plant ET data, calculating a crop coefficient (Kc), preparing graphs, organizing a digital presentation, and presenting the findings to commercial nursery participants and instructors. When averaged across days and pot sizes, ET of japanese honeysuckle was 1.22 cm·d−1, whereas ET of apache plume was only 0.80 cm·d−1. This finding supported the students' hypothesis that a nursery block of potted mesic vines would use more water than a nursery block of potted xeric shrubs per unit of ground area. Commercial nursery participants adopted the ET monitoring technique after viewing the student presentation, indicating effective transfer of information by the students. The simple, inexpensive, 3-week exercise furthered the students' horticulture knowledge and comprehension while allowing for a collaborative effort with the local nursery industry.