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  • Author or Editor: Benjamin Mullinix Jr x
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The xylem water potential of leaves of peach [Prunus persica (L.) Batsch] was lower for trees with moderate to high counts of the phony peach disease organism in roots during the day in September and October (P = 0.1%), after bloom in March (P = 3%), and before harvest in May (P = 1%). No significant differences occurred for predawn measurements on any date, during periods of rapid shoot growth in June, and for measurements made on terminal twigs in January. Experimental results suggest that the phony disease organism invades and clogs the new xylem each year. The internal water stress that results when the tree transpires produces the fruit and shoot symptoms known as phony disease of peach.

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Observations in controlled field experiments over 5 years indicated that imidacloprid, applied as a soil drench around the trunks of peach (Prunus persica), nectarine (P. persica var. nectarine) and japanese plum (P. salicinia) trees at planting and in the early spring and mid-summer for two subsequent seasons (0.7 g/tree a.i.), slowed the development of symptoms of phony peach disease (PPD) and plum leaf scald (PLS) (Xylella fastidiosa) in the trees. After 3.5 years, the percentage of peach trees showing PPD symptoms was 8.5% for the imidacloprid-treated trees compared to 34.3% for untreated trees. After 4.5 years, the percentage of peach trees showing PPD symptoms was 13.1% in the treated trees and 71.4% in the untreated trees. After 3.5 years, nectarine trees in untreated and treated plots showed PPD symptoms in 8.3% and 0.9% of the trees, respectively. After 4.5 years, PPD symptoms in nectarine were found in 32.3% of the untreated trees and 8.5% of the treated trees. Development of PLS disease in plum was also slowed by the trunk drench with imidacloprid in two japanese plum varieties. After 3.5 years, dieback was observed in 55% of the twigs of untreated and 23% of the twigs of treated trees of `Au Rosa' plum and 33% of the twigs of untreated and 12% of the twigs of treated trees of `Santa Rosa' plum.

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Bahiagrass (Paspalum notatum Flugge cv. Paraguayan-22) growing under newly planted peach [Prunus persica (L.) Batsch.] trees severely stunted the trees. Neither supplemental fertilizer nor irrigating with two 3.8-liters·hour-1 emitters per tree eliminated tree stunting emitters were controlled by an automatic tensiometer set to maintain 3 kpa at a depth of 0.5 m under a tree in bahiagrass. Preplant fumigation with ethylene dibromide at 100 liters·ha-1 increased tree growth, but not tree survival. Fenamiphos, a nematicide, applied under the trees each spring and fall at a rate of 11 kg-ha -1 had no positive effect on tree survival, tree growth, or nematode populations. Bahiagrass tended to suppress populations of Meloidogyne spp. under the trees., Meloidogyne spp. were the only nematodes present that had mean populations > 65 per 150 cm3 of soil. Leaf concentrations of several elements differed between trees growing in bahiagrass sod and in. bare ground treated with herbicides. Leaf Ca was low for all treatments in spite of a soil pH near 6.5 and adequate soil Ca. The severe stunting of trees grown in bahiagrass, irrespective of the other treatments, demonstrated that bahiagrass should not be grown under newly planted trees. The low populations of parasitic nematodes in bahiagrass showed that bahiagrass has potential as a preplant biological control of nematodes harmful to peach trees. Chemical name used: ethyl 3-methy1-4-(methylthio) phenyl (1-methylethyl) phosphoramidate (fenamiphos).

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Mechanical harvesting systems for processed blueberries (Vaccinium spp.) are available. However, low harvest efficiency and high fruit damage have limited the use of mechanical harvesters for picking blueberries for fresh market to specific cultivars under good weather conditions. New harvesting technology for fresh-market blueberries is needed. The V45 harvester was developed by the U.S. Department of Agriculture in 1994 to harvest fresh-market-quality northern highbush (V. corymbosum) blueberries in Michigan. The current study was performed in Georgia to evaluate the V45 harvester on specially pruned rabbiteye blueberry [V. virgatum (syn. V. ashei)] and southern highbush blueberry (V. darrowi × V. corymbosum) and included analysis of harvest efficiency and fruit quality (percent blue fruit, percent bloom, percent split skin, and internal bruise damage). Six-year-old, 6- to 8-ft-tall ‘Brightwell’ and ‘Powderblue’ rabbiteye blueberry plants were winter pruned to remove vertically growing and overarching canes in the center of the bush in Jan. 2004 and Feb. 2005 respectively. Three-year-old, 3- to 5-ft-tall ‘FL 86-19’ and ‘Star’ southern highbush blueberry plants were similarly pruned in summer (June 2004) or in winter (Feb. 2005). Pruning removed an estimated 30% to 50% of the canopy and opened the middle, resulting in V-shaped plants in both rabbiteye and southern highbush blueberries. Yield of winter-pruned ‘Brightwell’ rabbiteye blueberry was lower compared with unpruned plants during both years, but winter-pruned ‘Powderblue’ rabbiteye blueberry plants produced as much as unpruned plants in 2005. In ‘FL 86-19’ southern highbush blueberry, plants that were summer pruned in June 2004 produced as much as unpruned plants in 2005, but plants that were winter pruned in Feb. 2005 had lower yields than unpruned plants in 2005. The V45 harvester caused little cane damage on pruned blueberry plants. In rabbiteye blueberries, internal fruit damage and skin splitting was less in V45-harvested fruit than in fruit harvested by a sway harvester and nearly that of hand-harvested fruit. However, in ‘FL 86-19’ southern highbush blueberry, the V45 harvester detached a lower percentage of blue fruit and excessive amounts of immature and stemmed fruit. These findings suggest that the V45 harvester has the potential to harvest some rabbiteye blueberry cultivars mechanically with fruit quality approaching that of hand-harvested fruit.

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