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Charles A. Powell, Peter J. Stoffella, and Harry S. Paris

Zucchini squash (Cucurbita pepo L.) fruit yield and the incidence of sweetpotato whitefly (SPWF) [Bemisia tabaci (Gennadius)], squash silver leaf (SSL) disorder, and zucchini yellow mosaic virus (ZYMV) were measured during Spring and Fall 1991 in experiments containing various plant populations. In both experiments, as the within-row spacing increased from 30.5 to 76.2 cm or the number of plants per hill decreased from three to one, the number of marketable fruit per hectare decreased, and the marketable fruit per plant increased. Adult SPWF populations increased with decreased within-row spacing in the spring but not the fall experiment. The incidence of SSL or ZYMV infection was not affected by plant population in either experiment. The results indicate that increasing zucchini squash plant population can increase yield without affecting the incidence of SSL or ZYMV.

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W.A. Dozier Jr., A.W. Caylor, D.G. Himelrick, A.A. Powell, A.J. Latham, J.A. Pitts, and J.A. McGuire

Own-rooted, 4-year-old kiwifruit plants [Actinidia deliciosa (A. Chev.) C.F. Liang et R. Ferguson var. deliciosa] protected by a Styrofoam insulation wrap with a water-filled pouch (Reese clip-on trunk wrap) or by microsprinkler irrigation sustained less freeze injury than unprotected plants under field conditions at temperatures as low as -17.8C. Trunk splitting occurred on the plants, but no injury was detected on canes, buds, or shoots in the canopy of the plants. Unprotected plants had more trunk splitting and at greater heights than protected plants. New canes developed from suck- ers of cold-injured plants and developed a trellised canopy the following season.

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Charles A. Powell, Michael S. Burton, Robert Pelosi, Mark A. Ritenour, and Robert C. Bullock

Population density of citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), was monitored in a Florida citrus grove for 5 years by scouting weekly for larval-induced mines (leafminer-created tunnels in the leaves) in a replicated citrus plot treated with seven insect control regimes: Admire (imidacloprid) applied at 12, 6, 3, or 2-month intervals; Temik (aldicarb) applied annually; Metasystox-R (oxydemeton-methyl) applied annually; or no insect control. Leafminer populations were highest during the warmer months (April to September) and lowest during the cooler months (November to March). Populations peaked during June in all 5 years monitored. Trees treated with Temik or Metasystox-R had the same number of mines as the untreated controls. A biannual treatment with Admire reduced leafminer damage (number of mines) all 5 years compared with the controls. Additional Admire applications further reduced damage during some, but not all, years. A single application of Admire significantly reduced mines in 3 of the 5 years.

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Allison D. Oakes, Tyler Desmarais, William A. Powell, and Charles A. Maynard

Many hardwood tree species are being threatened by exotic pests, and for some, only genetic engineering can offer a solution before functional extinction occurs. An example of how genetic engineering can be a useful tool for forest restoration is the transgenic american chestnuts, which contain a wheat oxalate oxidase gene conferring resistance to the chestnut blight. Many hundreds of these trees are needed for field trials and eventual restoration plantings throughout its natural range, but production is bottlenecked because of the difficulty of making hardwood trees produce roots through micropropagation. The presence of roots and living shoot tips precede successful acclimatization of tissue culture-produced american chestnut plantlets. In these experiments, we attempted to improve the post-rooting stage of our american chestnut propagation protocol. We examined vessel type, hormone, and activated charcoal concentrations, and using a vermiculite substrate. For plantlets with the best combination of roots and living shoot tips we recommend using semisolid post-rooting medium containing 2 g·L−1 activated charcoal and 500 mg humic acid in disposable fast-food takeout containers. When using vermiculite as a substrate, adding 2.0 g·L−1 activated charcoal to post-rooting medium without a gelling agent was the preferred treatment. Improving the survival rates of the american chestnut plantlets will benefit the american chestnut restoration project by providing more plant material for both ecological studies and eventual restoration, since pursuit of a nonregulated status for these transgenic trees will require extensive field testing. These procedures may also be applicable to other difficult-to-root hardwood trees in transgenic programs, such as american butternut, white oak, and black walnut.

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Charles A. Powell, Michael S. Burton, Robert R. Pelosi, Phyllis A. Rundell, Mark A. Ritenour, and Robert C. Bullock

The population densities of the brown citrus aphid (BrCA) (Toxoptera citricidus Kirkaldy) and the spirea aphid (SA) Aphis spiraecola Patch were monitored by scouting weekly for 6 years in a replicated citrus plot treated with 7 insect control regimes: Admire (imidacloprid) applied at 12, 6, 3, or 2 month intervals; Temik applied annually; Meta-Systox-R applied annually; or no insect control. The numbers of both aphid species varied greatly from month to month and year to year. The brown citrus aphid was normally only detected in the fall (August through December) with populations peaking in September, October, or December depending on the year. The spirea aphid could be detected throughout the year during years when overall populations were high. Spirea aphid populations often peaked both in the spring and fall. Annual applications of Temik or Metasystox were ineffective in reducing aphid populations. Generally, all four Admire treatment regimes controlled aphids, although at least 2 annual Admire treatments per year were required to control the spirea aphid during some years.

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C.A. Powell, R.R. Pelosi, M.S. Burton, P.A. Rundell, M.A. Ritenour, and R.C. Bullock

The effectiveness of seven different aphid control regimes in delaying movement of decline (DI) and nondecline (NDI) inducing isolates of citrus tristeza virus (CTV) into a CTV-free sweet orange scion on sour orange rootstock block was monitored annually for 5 years beginning in 1999, 2 years after the introduction of the brown citrus aphid (BrCA) into the region. After 5 years, the mean percentages of infection with DI CTV were 19, 19, 17, 29, 23, 19, or 14 for trees treated annually with imidocloprid, every 6 months with imidocloprid, every 3 months with imidocloprid, every 2 months with imidocloprid, annually with Temik, annually with Meta Systox-R, or untreated, respectively. The mean percentages of infection (after 5 years) with only NDI isolates of CTV for the seven treatments were 40, 31, 33, 38, 38, 38, or 33. There was no significant difference (after 5 years) among either the DI or NDI CTV treatment means. The overall 5-year infection percentage for DI CTV (20%) was somewhat lower than that reported before the introduction of the BrCA (27%) (11). Aphid densities (Toxoptera citricidus and Aphis spiraecola) varied considerably from year to year. Good aphid control was achieved with all four imidocloprid treatments, but not with Temik or Meta Systox-R. The level of aphid control did not influence overall CTV infection percentages.

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R.C. Ebel, W.A. Dozier Jr., M.L. Nesbitt, N.R. McDaniel, A.A. Powell, A. W. Caylor, and W.R. Okie

There are a limited number of peach and nectarine cultivars available with chilling requirements that perform well in the Gulf Coast area of Alabama. A test planting of 40 peach and 13 nectarine cultivars was established in 1985 at the Gulf Coast Substation at Fairhope, Ala. The plot was prepared and trees grown according to commercial procedures. Blocks of four trees of each cultivar were planted on a 6 x 6-m spacing. Chill hours were calculated each year based on number of hours at or below 7.3 °C; starting from and including the first 10 consecutive days a total of 50 hours were accumulated to 15 Feb. Data collected included date of full bloom, first harvest date, and total yield. Fruit were measured or rated for skin color, attractiveness, firmness, stone freeness, pubescence, flesh color, dessert quality, shape, weight, percentage with split pits, and occurrence of malformed sutures and extended tips. All cultivars were evaluated for 9 years (1987–95). The best performing varieties are discussed.

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J.M. Goatley Jr., A.J. Powell Jr., W.W. Witt, and M. Barrett

Chlorsulfuron, diclofop, and sulfometuron were evaluated for potential use in selective control of tall fescue (Festuca arundinacea Schreb.) in Kentucky bluegrass (Poa pratensis L.). Polynomial trend analyses indicated highly significant linear and quadratic response curves for percentage of tall fescue reduction for each herbicide. Fall and spring treatments with chlorsulfuron and diclofop provided significant tall fescue control, with slight to moderate initial Kentucky bluegrass phytotoxicity. Fall and spring applications of sulfometuron resulted in excellent tall fescue control, but initial Kentucky bluegrass damage was severe and would be unacceptable for high maintenance turf. Chemical names used: 2-chloro- N -[[(4-methoxy-6-methyl-l,3,5-triazin-2-yl)amino]carbonyl]-benzenesulfonamide (chlorsulfuron); 2-[4-(2,4-dichlorophenoxy)phenoxy]proponoate (diclofop); N -[[(4,6-dimethylpyrimidin-2-yl)amino]carbonyl]-2-methoxycarbonyl-benzenesulfonamide (sulfometuron).

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J.M. Vogel, A. Rafalski, M. Morgante, G. Taramino, W. Powell, M. Hanafey, and S.V. Tingey

DNA-based diagnostics are now well-established as a means to assay diversity at the locus, chromosome, and whole-genome levels. As technology has advanced, DNA sequence-based assays have become easier to use, more efficient at screening for nucleotide sequence-based polymorphisms, and available to a wider cross-section of the research community. A review of the use of molecular markers in several different areas of genetics and plant breeding will be presented, as well as a discussion about their advantages and limitations. Recent advances in several areas of technology development and laboratory automation will also be presented, including a summary of direct comparison of different DNA marker systems against a common set of soybean cultivars.

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J.M. Vogel, A. Rafalski, W. Powell, M. Morgante, C. Andre, M. Hanafey, and S.V. Tingey