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Dennis E. Deyton, Carl E. Sams and John C. Cummins

Treatments of single applications of 0%, 3%, 6%, 9%, or 12% dormant oil were sprayed on peach (Prunus persica L. Batsch) trees on 6 Feb. 1990. A repeat application of 6% oil plus 6% oil applied 6 days later was also made. Internal CO 2 concentrations of oil-treated buds and twigs were higher than the control the day after treatment and continued to be higher for 6 days. The second application of 10% oil prolonged the elevated CO2 concentration. Applications of 9% or 12% oil delayed flower bud development and bloom. The repeated application of 6% oil delayed bud development and bloom more than a single application of 6% oil. Damage to fruit buds increased as oil concentration increased, but repeated application of 6% oil resulted in less damage than a single application of 12% oil.

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Dennis E. Deyton, Carl E. Sams and John C. Cummins

Foliar sprays of increasing concentrations (0, 75, 150, 300, 600, and 1200 mg·liter-1) of paclobutrazol were applied to `Cardinal' strawberry plants (Fragaria × ananassa Duch.) 35 days after transplanting. The plants were established in August in cultivated plots for measurement of paclobutrazol effects on first year growth or in a double-row hill system on black polyethylene-covered raised beds for 2nd year measurements. Increasing the paclobutrazol concentration reduced the number of runners, decreased runner length, and limited biomass partitioned into daughter plants. By the end of the first growing season, paclobutrazol had increased lateral crown development but reduced leaf area per treated plant. Root growth was reduced by concentrations >600 mg·liter-1. Treatment with 75 to 300 mg·liter-1 increased total plant dry weight by 33% to 46%. The following spring, plant growth was decreased by ≥ 300 mg·liter-1. Yield was increased by all treatments, except 1200 mg·liter-1. Leaf net photosynthesis increased within 12 days after treatment with paclobutrazol and was higher than in the controls the next summer. Leaf stomata1 conductance also increased the first year and was significantly higher the 2nd year after treatment. The optimum concentration of paclobutrazol for strawberries appears to be between 150 and 300 mg·liter-1.

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Dennis E. Deyton, Carl E. Sams and Mark T. Windham

Field-grown dogwood trees in a commercial nursery were sprayed with 0%, 1%, or 2% soybean oil emulsified with Latron B-1956 at 2-week intervals from 10 June until 19 Aug. 1998. In 1999, dogwood trees were sprayed with 0%, 1%, 1.5%, 2%, or 2.5% emulsified soybean oil at 2-week intervals from 22 June until 26 Aug. The trials had treatments arranged in randomized complete-block designs with eight trees per block and six and four replications in 1998 and 1999, respectively. Disease severity of powdery mildew was estimated using the following scale: 0 = healthy, 1 < 2%, 2 < 10%, 3 < 25%, 4 < 50%, 5 > 50%, and 6 = 100% of foliage with symptoms or signs of powdery mildew. In 1998, trees sprayed with soybean oil had higher net photosynthesis rates and more caliper and height growth than control trees. Untreated trees and ≈25% of foliage infected with powdery mildew on 8 July, while trees sprayed with 1% or 2% soybean oil had about 2% of leaves infected. In 1999, the powdery mildew was already present on foliage (wet spring) when the first application of oil was made. Repeated sprays of soybean oil did not reduce the incidence of powdery mildew. Thus, soybean oil appeared to provide protective control of powdery mildew but not curative control of a heavy infestation of the fungi. Photosynthesis was increased by soybean oil for the first month of spraying in 1999, but did not differ after that. Repeated applications of even the high rates of oil did not cause phytotoxicity.

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Dennis E. Deyton, Carl E. Sams and John C. Cummins

Treatments of dormant oil, at rates of 0, 3, 6, 9, or 12 % (v/v), were sprayed until drip on four year old `Biscoe' peach trees on February 6, 1990. Another treatment was applied as a split application with 6 % applied on the previous application date and a second application of 6% solution applied on February 12. The internal atmosphere of bud and twig was modified by the oil treatment. The internal concentration of CO2 was elevated the morning following treatment and continued higher than the control for seven days. A second application Of 6% oil resulted in additional elevation of internal CO2. External evolution of CO2 of all oil treated twigs was 6 to 18% lower than the control 8 days after treatment. Bud phenology and bloom date of trees receiving higher rates of oil were slightly delayed.

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Joanne Logan, Dennis E. Deyton and David W. LockWood

Peach [Prunus persica (L.) Batsch] production in Tennessee has declined since 1985 due to the occurrence of freezing temperatures that kill the buds, usually in the spring. Analyses of long-term (1951-89) daily temperature data from four locations in Tennessee were used to evaluate the freeze risks for `Redhaven' peach tree buds at those sites. A model using daily accumulated chill units and growing degree hours (base 4.4C air temperature) was used to estimate the dates to begin and end chill unit accumulations and the dates of full bloom of `Redhaven' peach trees for each year in the climatological record. The actual dates of freezes with air temperatures at or below –2.2C and the estimated bud developmental stage on the date of each freeze also were determined. The model was tested using peach orchard records and was found to be an improvement over using only freeze data. The model indicated that Spring Hill had the highest risk for peach production and Jackson the lowest. Recent problems with spring freezes at Knoxville and Spring Hill were due to later than normal freeze dates rather than earlier development of the `Redhaven' peach tree buds. At Springfield, the recent freeze problems were due to earlier breaking of rest, earlier full bloom, and later freezes.

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Dennis Deyton, Carl E. Sams, Jim R. Ballington and John Cummins

Trials were conducted in 2004 to compare the effects of soybean oil formulations and concentrations on flowering and fruit thinning of rabbiteye and southern highbush blueberries. Mature `Climax' bushes near Spring City, Tenn., were sprayed to runoff on 10 Feb. with water, or 9% soybean oil in the formulations TNsoy11, TNsoy12, TNsoy13, TNsoy14, or Golden Natur'l (GN). In a second trial, 3-year-old `Legacy' southern highbush plants at Spring Hill, Tenn., were sprayed on 11 Feb. with 0%, 6%, 9%, 12%, and 15% GN. A similar trial was sprayed on 5 Mar. at Fletcher, N.C., using young plants of various Southern highbush cultivars. Each formulation of soybean oil (9%) delayed bud development and flower anthesis of `Climax' bushes. Bloom opening on `Legacy' bushes was delayed by 2 to 6 days with sprays of ≥9% GN, with higher concentrations causing more delay. However, flower bud mortality of `Legacy' plants was greater when sprayed with the higher oil concentrations. `Legacy' plants sprayed with 0%, 6%, and ≥9% oil had 0%, 30% and ≥70% bud mortality, respectively, at 36 days after treatment. `Legacy' plants sprayed with 12% and 15% oil sprays had an estimated 24% and 13%, respectively, of a crop load compared to the estimated 100% crop load on control plants. Flower bud development, flower bud mortality, crop load and berry size (across cultivars) of Southern highbush cultivars at Fletcher were not affected by oil treatments. Results were variable among trials, perhaps due to factors such as cultivars, timing of application (date), maturity of plants, environmental conditions, etc. There is potential for soybean oil formulations to be used as a chemical thinner as well as to delay blooming.

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Dean A. Kopsell, Carl E. Sams, T. Casey Barickman, Dennis E. Deyton and David E. Kopsell

Selenium (Se) is an essential mammalian micronutrient. Adult humans have a daily requirement of 55 to 70 μg/day Se depending on sex and pregnancy/lactation for females. In addition, recent studies have shown health benefits with dietary Se supplementation of 100 to 200 μg/day Se. However, daily intakes in humans greater than 900 μg Se will result in toxicity called selenosis. Although not essential in plant nutrition, some species can bioaccumulate Se. Brassica and Allium species became prime candidates for Se enrichment because of their ability to accumulate and tolerate high concentrations of Se in edible tissues; however, there is now concern that these species are too efficient at selenization and overconsumption of their selenized tissues could result in selenosis. Herbal crop species are consumed regularly in the diet for their culinary flavor attributes. Basil (Ocimum basilicum L.) and cilantro (Coridandrum sativum L.) are not classified as Se accumulators. Therefore, a study was undertaken to determine the potential to selenize basil and cilantro through foliar Se applications to consistently supplement diets with nutritionally beneficial levels of Se. Plants of each species were grown in both growth chamber and field environments and treated with foliar applications (5 mL per plant) of selenate-Se and selenite-Se at concentrations of 0, 2, 4, 8, 16, and 32 mg·L−1 Se. Crops received three separate foliar applications at ≈5-day intervals beginning 24 to 28 days after planting for the growth chamber plants and 50 days after planning for the field environment. Selenium accumulation in both basil and cilantro leaf tissues increased linearly under both selenate-Se (P ≤ 0.001) and selenite-Se (P ≤ 0.001) foliar treatments in growth chamber and field evaluations. Maximum Se leaf tissue concentrations for basil and cilantro ranged from 13 to 55 μg·g−1 Se dry weight. Selenization of basil and cilantro is possible through foliar Se applications, and Se fortification of herbal crops may provide alternative delivery systems in human diets.

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Dennis E. Deyton, Renae E. Moran, Carl E. Sams and John C. Cummins

Applications of soybean oil to dormant peach [Prunus persica (L.) Batsch] trees were tested for prebloom thinning of flower buds in five separate experiments. Data were combined from experiments in which 2.5% to 20% emulsified soybean oil was sprayed on `Belle of Georgia' or `Redhaven' trees. The number of dead flower buds was concentration-dependent with maximum bud kill of 53% occurring with application of 12% soybean oil. The amount of thinning was fairly consistent from year to year, ranging from 34% to 51% when 10% soybean oil was applied, but was less consistent when 5% was applied, ranging from 6% to 40%. Overthinning by midwinter applications of soybean oil occurred in one experiment when bud mortality on nontreated trees was 40% due to natural causes. Mild to moderate spring freezes occurred in three experiments, but did not reduce yield more in soybean oil–thinned than in nontreated trees. Flower bud survival was improved when trees were sprayed with 10% or 12% soybean oil prior to a –4 °C spring frost. Applications of soybean oil to dormant trees thinned flower buds, reduced the amount of hand thinning required, and hastened fruit maturity.

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Renae E. Moran, Dennis E. Deyton, Carl E. Sams, Charles D. Pless and John C. Cummins

Soybean [Glycine max (L.) Merrill] oil was applied to apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] as a summer spray in six studies to determine if it controls European red mites [Panonychus ulmi (Koch.)], how it affects net CO2 assimilation (A), and if it causes phytotoxicity. Sprays of 0.5%, 1.0%, and 1.5% soybean oil {TNsoy1 formulation [soybean oil premixed with Latron B-1956 (LAT) spreader-sticker at 10 oil: 1 LAT (v/v)]} reduced mite populations by 94%. Sprays of 1% and 2% soybean oil reduced mite populations to three and four mites per leaf, respectively, compared to 25 per leaf on water-sprayed plants. Soybean oil concentrations of 1.0% and 1.5% applied to whole trees reduced A for less than 7 days. Phytotoxicity did not occur when soybean oil was applied with an airblast sprayer at concentrations of 1.0% and 1.5% or with a mist bottle at 2%. Phytotoxicity occurred when soybean oil was applied with a mist bottle at 4% and 6%, which left soybean oil leaf residues of 0.22 to 0.50 mg·cm-2. No phytotoxicity occurred with 4% SunSpray, which resulted in a mean leaf residue of only 0.13 mg·cm-2. Spraying 1% soybean oil tended to give better mite control than 1% SunSpray Ultra-Fine oil, but caused greater oil residues and a greater reduction in A.

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Robert Pendergrass, Roland K. Roberts, Dennis E. Deyton and Carl E. Sams

Using soybean oil to control insect pests, delay bloom, and thin fruit in peach [Prunus persica (L.) Batsch] production could reduce yield losses and fruit thinning costs compared to the current practice of using petroleum oil spray to control insect pests alone. The higher annua cost of soybean oil spray compared to petroleum oil spray was more than offset by higher average annual revenue from increased peach yields and lower thinning costs. At one location, soybean oil to delay bloom and thin fruit unambiguously reduced production risk. At another location, both mean and variance of returns were higher, but a lower coefficient of variation suggested lower relative risk for the soybean oil spray alternative. Risk resulting from the unanticipated influence of weather and mismanagement on the effectiveness of soybean oil spray were not considered in this analysis. More research is needed to hone in on the optimum soybean oil spray rates under alternative environmental and management conditions.