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Tifton, Georgia

Johnson III W.C.,USDA ARS | Davis J.W.,University of Georgia
HortTechnology | Year: 2014

Timely cultivation with a tine weeder and hand weeding are the primary tools for successful weed control in organic sweet onion (Allium cepa), but conditions frequently arise that delay the initial cultivation. Weeds that emerge during the delay are not effectively controlled by cultivation and herbicides derived from natural products may have a role to control the emerged weeds. It has been reported that clove oil herbicide was more effective when sprayers were calibrated for higher output (>50 gal/acre) compared with sprayers calibrated at ≈25 gal/acre. However, when clove oil was applied at the recommended rate of 10% by volume, herbicide cost was doubled when sprayer output volume was doubled. It was theorized that herbicide adjuvants might improve clove oil efficacy and reduce weed control cost by not needing to increase sprayer output volume. Trials were conducted from 2010 to 2012 to evaluate all possible combinations of two sprayer output volumes and five herbicide adjuvants used with clove oil (10% by volume) for cool season weed control. Sprayer output volumes evaluated were 25 and 50 gal/acre, using spray tips of differing orifice size. Adjuvants evaluated were a material composed of saponins, citric acid plus garlic extract, an emulsified petroleum oil (EPO) insecticide, a conventional petroleum oil adjuvant (POA), no adjuvant used with clove oil, and a nontreated control. Weed control was not consistently improved by applying clove oil (10% by volume) with a sprayer calibrated at 50 gal/acre compared with sprayer calibrated at 25 gal/acre. Improvements in weed control that were occasionally seen did not affect onion yield. Adjuvants provided minimal improvement in weed control from clove oil and did not consistently improve onion yield. Based on these results, clove oil does not provide suitable levels of weed control in organic Vidalia® sweet onion production to justify the expense.

Brennan E.B.,USDA ARS | Boyd N.S.,Dalhousie University | Smith R.F.,University of California Cooperative Extension | Foster P.,Phil Foster Ranches
Agronomy Journal | Year: 2011

Rye (Secale cereale L.) is an important cover crop in high-value vegetable production in California. A 2-yr winter study on organic farms in Salinas and Hollister, CA evaluated cover crop population densities, ground cover, aboveground dry matter (DM), and N content of rye and five legume-rye mixtures. Mixtures had 60 or 90% legumes by seed weight and included twoor more of the following legumes: faba bean (Vicia faba L.), vetches (V. benghalensis L., V. dasycarpa Ten., V. sativa L.), and pea (Pisum sativum L.). Seeding rates were 90 (rye) and 140 (mixtures) kg ha-1, and densities were 142 to441 plants m-2. Early-season ground cover was usually greater in monoculture rye and the 60% legume mixtures than the 90% legume mixtures. Total DM, and legume and rye DM in mixtures diff ered by year, site, harvest, and cover crop. Total DM was usually at least twotimes higher at season end than mid-season. Th e 90% legume mixtures generally produced more legume DM than the 60% legume mixtures, but legume DM usually declined aft er mid-season. Rye DM increased with rye density. Total cover crop N uptake was greater in Hollister than Salinas; however, legume DM and legume N uptake were greater in Salinas. Interactions between site, year, cover crop, and harvest illustrate the complex growth dynamics of legume-rye mixtures. Th e 90% legume mixtures appear most suitable for vegetable production in California because they had a better balance of legume and rye DM at season end. © 2011 by the American Society of Agronomy.

Hart J.P.,USDA ARS | Griffiths P.D.,Cornell University
Plant Genome | Year: 2015

Since its emergence in 2001, an aphid-transmitted virus disease complex has caused substantial economic losses to snap bean (Phaseolus vulgaris L.) production and processing in the Great Lakes Region of the United States. The general ineffectiveness of chemical control measures for nonpersistently transmitted viruses established an urgent need for the development and deployment of cultivars with resistance to the component viruses. Our objectives were to further characterize the inheritance of resistance to Bean yellow mosaic virus (BYMV), which is conditioned by the By-2 allele, to adapt genotyping-by-sequencing (GBS) to common bean to discover and genotype genome-wide single nucleotide polymorphisms (SNPs) in a set of recombinant inbred lines (RILs) derived from an introgression program, and to enable and validate marker-assisted selection for By-2. We optimized ApeKI for GBS in common bean and retained 7530 high-quality SNPs that segregated in our introgression RILs. A case–control genomewide association study (GWAS) was used to discover 44 GBS SNPs that were strongly associated with the resistance phenotype and which delimited a 974 kb physical interval on the distal portion of chromosome 2. Seven of these SNPs were converted to single-marker Kompetitive Allele-Specific Polymerase chain reaction (KASP) assays and were demonstrated to be tightly linked to BYMV resistance in an F2 population of 185 individuals. This research enables marker-assisted selection of By-2, provides enhanced resolution for fine mapping, and demonstrates the potential of GBS as a highly efficient, high-throughput genotyping platform for common bean breeding and genetics. © Crop Science Society of America.

Chaudhury M.F.,U.S. Department of Agriculture | Sagel A.,USDA ARS | Skoda S.R.,U.S. Department of Agriculture
Journal of Medical Entomology | Year: 2012

The waste artificial larval rearing media of New World screwworms, Cochliomyia hominivorax (Coquerel) were evaluated to determine their effectiveness as oviposition attractants. Various concentrations of waste larval media resulting from rearing screwworm larvae in gel and cellulose fiber-based artificial diets tested over a 4-wk period attracted varying number of gravid screwworm flies to oviposit. Three-day-old waste medium with concentrations of 10 and 25% were most attractive to gravid female flies for oviposition and resulted in the most oviposition. One and 7-d-old wastes at all concentrations were less attractive for oviposition than the 3d-old media. The fresh (0-d-old), 14-d- and 28-d-old waste media were the least attractive substrates for oviposition. The waste from the cellulose fiber-based diet resulted in significantly more oviposition compared with waste from the gel-based diet. Microorganisms growing in the waste media probably produce metabolites that attract gravid screwworm flies to oviposit. Use of the waste products of appropriate age and dilution as oviposition substrates would enhance oviposition in mass production colony cages. © 2012 Entomological Society of America.

Fritz B.K.,U.S. Department of Agriculture | Hoffmann W.C.,U.S. Department of Agriculture | Bagley W.E.,Wilbur Ellis | Kruger G.R.,University of Nebraska - Lincoln | And 2 more authors.
Atomization and Sprays | Year: 2014

With a number of new spray testing laboratories going into operation and each gearing up to measure spray atomization from agricultural spray nozzles using laser diffraction, establishing and following a set of scientific standard procedures is crucial to long-term data generation and standardization across the industry. It has long been recognized that while offering ease of use as compared to other methods, laser diffraction measurements do not account for measurement bias effects due to differ-ential velocities between differing sized spray droplets, and in many cases significantly overestimate the fine droplet portion of the spray. Droplet sizes and velocities were measured for three agricul-tural flat fan nozzles (8002, 8008, and 6510) each at three spray pressures (138, 276, and 414 kPa) at four downstream distances (15.2, 30.5, 45.7, and 76.2 cm) across a range of concurrent air velocities (0.7-80.5 m/s). At air velocities below 6.7 m/s, large gradients in droplet velocities resulted in over-estimation of both the 10% volume diameter (Dv0:1) by more than 10% and the percent volume of the spray less than 100 m (V<100) was overestimated two-to three-fold. The optimal measurement dis-tance to reduce droplet measurement bias to less than 5% was found to be 30.5 cm with a concurrent air velocity of 6.7 m/s for measuring droplet size from ground nozzles. For aerial spray nozzles, the optimal distance was 45.7 cm. Use of these methods provides for more accurate droplet size data for use in efficacy testing and drift assessments, and significantly increases inter-lab reproducibility. © 2014 by Begell House, Inc.

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