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G.E. Boyhan, J.D. Norton and J.A. Pitts

The dwarfing characteristics of St. Julien and Pixy rootstocks, measured by shoot growth, were evident with `AU-Amber' and `AU-Producer' plum (Prunus salicina Lindl.) scions. Dwarfing did not occur with `AU-Rubrum'. Trunk cross-sectional area (TCA) was reduced with `AU-Amber', `AU-Producer', and `AU-Rubrum' scions on St. Julien and Pixy rootstocks. After 3 years, tree survival was 94% for Lovell; 89%, Halford; 57%, Nemaguard; 75%, Nemared; 83%, St. Julien; and 47%, Pixy. Tree survivability was significantly lower on Nemaguard and Pixy rootstocks than on Lovell and Halford. Multiple regression of total shoot growth, TCA, and survivability against foliar nutrient content resulted in the following significant equations: 0.460Mg - 0.210Mn, 0.236B - 0.487Mn, and 0.359N + 0.398Ca - 0.267P - 0.360Fe for each, respectively. Growth, survivability, and foliar nutrient content are significantly affected by rootstock in plum production.

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J.D. Norton, G.E. Boyhan and J.A. Pitts

The dwarfing characteristics of St. Julien and Pixy rootstocks as measured by shoot growth and trunk cross-sectional area (TCSA) was evident. Tree survival was significantly reduced after 3 years on Nemaguard and Pixy rootstocks. None of the elements measured by foliar nutrient analysis were below the minimum for plums; however, significant multiple regression equations for total shoot growth, TCSA, and survivability were evident with R 2 of ≈0.30 in all three cases.

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R.C. Ebel, D.G. Himelrick, A. Caylor and J. Pitts

The surfactant “Surfactant WK” (dodecyl ether of polyethylene glycol) was applied to peach trees [Prunus persica (L.) Batsch] at full bloom over 3 years. Blossoms died rapidly so that within 2 days dead blossoms could be distinguished easily from live blossoms or set fruit. There were strong (R 2 > 0.87), linear correlations between concentration of “Surfactant WK” applied and percent blossoms removed and fruit set, which were similar over the 3 years. Trees were hand-thinned according to commercial practices after treatment. There was similar cropload, fruit weight, and yield across treatments at harvest indicating no negative effects by the chemical on productivity. There was only slight limb damage at the highest concentrations of “Surfactant WK,” which overthinned blossoms. We recommend that based on the effectiveness, consistency, and lack of significant phytotoxicity, “Surfactant WK” be reevaluated as a thinning chemical for peach trees.

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A. Caylor, W. Dozier, D. Himelrick, J. Pitts and L. Chapman

Four year old `Loring' peach trees on `Lovell' rootstock were treated with single applications of 0, 50, and 100 ppm GA3 alone and in combination with 100 ppm ethephon on 15 November 1988, 1989, and 1990 to determine the effect on bloom delay the following spring. Flower bud number was not affected by any of the treatments the next spring. Ethephon had the greatest effect on bloom delay the following spring. The 50 and 100 ppm GA3 treatments resulted in a slight delay of bloom. The combination of 50 and 100 ppm GA3 and 100 ppm ethephon resulted in less of a bloom delay than ethephon alone but greater than the GA3 treatments alone. Fruit set was increased by ethephon treatments in 1989 and 1991 but not in 1990. Ethephon treatments delayed fruit maturity whereas GA3 did not. Total fruit yield for 1989, 1991, and the three year average was not effected by treatments. However, in 1990 50 ppm GA3 resulted in the highest yields. Ethephon treatments reduced the average fruit weight in 1990 and 1991 but not in 1989 or the three year average.

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A.W. Caylor, W.A. Dozier Jr. and J. Pitts

Latron AG-98 (formerly named Triton AG-98) was applied to 8-year-old `Surecrop' peach trees on Lovell rootstock at 0%, 2%, 4%, and 6% (v/v) on 13 Mar. 1990 and 1992 and 28 Mar. 1991. Our objective was to determine the effect Latron AG-98 had on percentage of blossoms removed, fruit set, total fruit count and yield, and marketable fruit weight. The percentage of blossoms removed increased with increasing rates of Latron AG-98. The 4% and 6% rates removed the greatest percentage of blooms in all 3 years. The number of fruit per 50 cm of shoot length, number of fruit removed by hand-thinning, percent fruit set, total fruit number, and total fruit yield decreased with increasing rates of Latron AG-98 in 1990 and 1992 but not in 1991. The marketable fruit weight increased with increasing rates of Latron AG-98 in 1990 and 1992 but not in 1991. Latron AG-98 was not effective in 1991 because of a 2-day delay in application. Latron AG-98 was effective in removing blossoms from `Surecrop' peach at all three rates. However, the 4% and 6% rates reduced the yields below a commercially acceptable level. The 2% rate of Latron AG-98 could be useful as a tool to reduce the labor required to hand-thin peaches.

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E.H. Simonne, J.T. Eason, J.A. Pitts and J.T. Owen

Bell pepper (Capsicum annuum L.) fruit are typically green in color at the immature stage, 1/3 and 2/3 colored during ripening, and red at maturity. However, this sequence does not apply to new varieties with immature colors of white or purple, intermediate colors of brown or black, and mature colors of yellow or orange. The study of physiological changes during ripening in such cultivars requires the description of color changes. Therefore, color changes of new bell pepper varieties were evaluated by subjective description and objective measurement of L, a, and b. Color changes were described with a five-color stage scale. L, a, and b were affected significantly by variety (P < 0.01), and a and b were affected significantly by color stage (P = 0.95, 0.01, and 0.01 for L, a, and b, respectively). Location and cultivar*location had no significant effect. For each cultivar, differences in a and b values defined color stages that were clearly identifiable. When plotted, color measurements (a and b) were in good agreement with the verbal descriptions. Therefore, measurements of L, a, and b are not systematically necessary when referring to bell pepper colors.

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G.E. Boyhan, J.D. Norton, B.R. Abraham and J.A. Pitts

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B.S. Wilkins, R.C. Ebel, W.A. Dozier, J. Pitts and R. Boozer

This study was conducted to determine efficacy of Tergitol TMN-6 in thinning peach blossoms. A pretest was conducted and demonstrated no difference between TMN-6 and TMN-10 in efficacy when applied at full bloom or petal fall and at rates of 20 and 40 mL·L-1. In the main test, Tergitol TMN-6 was sprayed once at 10, 20, or 30 mL·L-1 at full bloom or petal fall and compared to an unsprayed control for 3 years. Tergitol caused widespread necrosis of flower parts including sepals, petals, pistils, stamens and peduncles. There was a difference among chemical treatments with more fruit removed at higher concentrations, although the amount of fruit removed was similar for the 20 and 30 mL·L-1 rates. There was no difference in thinning response at full bloom or petal fall, indicating a wide window of efficacy. There was also a difference among years, which was apparently not related to temperature or relative humidity during time of application. Tergitol caused some leaf yellowing and tip burn especially at the higher rates when leaves were present, but the trees did not appear to be seriously affected. Fruit weight was either not affected or larger in some years from treatment. Unlike higher concentrations, tergitol at 10 mL·L-1 did not negatively impact fruit number per tree at harvest. At harvest, fruit weight, skin blush, firmness, and soluble solids at harvest were not affected by treatment. Tergitol TMN-6 proved to be an effective thinning agent and when applied from full bloom to petal fall at 10 mL·L-1 it did not adversely affect the tree or fruit.

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

The postemergence-active herbicides lactofen, fomesafen, and acifluorfen were applied to established matted-row strawberry plants (Fragaria × ananassa) and evaluated for broadleaf weed control and foliar phytotoxicity. Strawberries were evaluated for yield and fruit quality. Treatments were applied following June renovation. All herbicide treatments resulted in acceptable control of broadleaf weeds present at the time of application; however, sicklepod (Cassia obtusifolia) germinated after herbicide application. All treatments caused foliar injury within 3 days after application. No injury symptoms were evident 21 days after treatment due to new foliage development. Fomesafen and acifluorfen were the only herbicides to suppress runner count. Yields the following year were not reduced by herbicide treatments. Chemical names used: (±)-2-ethoxy-l-methy1-2-oxoethyl 5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitrobenzate (lactofen); 5-[2-chloro-4-(trifluoromethyl)phenoxy] -N -(methylsu1fonyl)-2-nitrobenzamide (fomesafen); 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid (acifluorfen).

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Thomas G. Beckman, Philip A. Rollins, James Pitts, Dario J. Chavez and Jose X. Chaparro

The primary focus of the stone fruit rootstock program at Byron, GA, has been the development of disease-resistant rootstocks for peach (Prunus persica L. Batsch). Historically peach tree short life (PTSL), aka bacterial canker complex, and Armillaria root rot (ARR) have been the two most important causes of premature mortality of commercial peach trees in the southeastern United States. Guardian®, a seedling peach rootstock, was cooperatively released in 1993 by the U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) and Clemson University. It has since been widely adopted by the southeastern peach industry. As a result, trees losses to PTSL have declined sharply. However, Guardian, like most other peach seedling rootstocks, is susceptible to ARR. ARR has now moved to the forefront as the primary cause of premature peach tree death in the Southeast. In response to this threat, the USDA-ARS in cooperation with the University of Florida, released ‘Sharpe’, a plum hybrid rootstock in 2007. Despite its broad disease resistance, ‘Sharpe’ proved unsuited for widespread commercial utilization due to its relatively poor cropping performance. In 2011, ‘MP-29’, a semidwarf, clonal, plum × peach hybrid, was released for commercial trial. ‘MP-29’s broad disease and nematode resistance, in combination with its dwarfing ability and excellent productivity, offered great promise for use in this production area and in others suffering from similar issues. Since its release, testing of ‘MP-29’ has continued both in researcher and grower trials. To date, performance has exceeded all expectations.