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  • Author or Editor: Dean R. Evert x
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Stem hydraulic conductivity of peach [Prunus persica (L.) Batsch] was lower in trees with phony disease than in healthy trees. This lower conductivity occurred in 1- to 4-year stems, in five cultivars, in two pruning systems, and from June through October. Leaf xylem pressure potential was lower in trees with phony disease than in healthy trees in each of the five cultivars tested and from June through September. The reduction in pressure potential in diseased trees exceeded any variations in pressure potential with cultivar or month. The area of functional xylem stained by dye was visibly smaller in stems from diseased trees than in healthy trees. These results were all consistent with the theory that symptoms of phony disease of peach are caused by xylem blockage.

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Weight and flesh firmness of peach fruit [Prunus persica (L.) Batsch ‘Junegold’] were measured at harvest from phony-infected and noninfected trees. Regression equations showed that fruit from phony-infected trees had an average increase in weight of 0.95 g to 1.03 g per newton decrease in flesh firmness at harvest, significantly less than the 1.69 g to 2.90 g increase per newton decrease for normal trees (P = 0.05). Internal moisture stress caused by xylem blockage in phony-infected trees may explain the changed flrmness/weight relationship during final swell.

Open Access
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Center-pivot irrigation during two radiation frosts in Mar. 1986 increased the temperature and reduced fruit injury in a wedge-shaped sector of a 6-year-old ‘Rio Grande’ peach [Prunus persica (L.) Batsch.] orchard. Irrigation increased temperatures under the pivot as much as 5°C during the –5.3° frost on 2 Mar. and 3° during the –2.8° frost on 23 Mar. The percentage of live fruit on 3 Mar. ranged from 35% on nonirrigated trees adjacent to the irrigated sector to 67% on trees in the middle of the irrigated sector (P < 0.01). The percentage of live fruit after the less severe frost on 23 Mar. ranged from 80% to 95% in the same locations (P > 0.05). The weight of fruit thinned on 21 Apr. was 18.2 kg for trees in the middle of the irrigated sector, 2.1 kg for trees along an edge of the irrigated sector, and 9.5 kg for nonirrigated trees adjacent to the irrigated sector (P < 0.05); therefore, injury likely was greater along the edge of the irrigated sector.

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Armothin® thinned `Sentinel' fruit on peach trees (Prunus persica L.) in 1993. Thinning increased as Armothin® rate in the single spray increased from 1.5X, to 3.0% to 6.0% (v:v) and as the percentage of open blossoms increased from 30% to 61%. The 1.5 % rate of Armothin® thinned significantly only on the third date, and the 6.0% rate overthinned slightly on the third date. Minor discoloration developed on the expanding leaves of a few of trees but disappeared in a few days. No leaf abscission occurred on treated trees and tree growth was normal. Variability between trees treated alike probably reflects the variability in bloom when sprayed. According to Akzo, Armothin® prevents pollination by reacting with the surface of the receptive stigma. Spraying after full bloom should selectively prevent fertilization of the last blossoms to open without destroying the fertilized fruit. This possibility will be tested in 1994. Armothin®, which is a contact thinner, seems to avoid the problems associated with thinners that act as growth regulators and with nonselective caustic thinners. Because of its low phytotoxicity and wide range of effective rates, Armothin® has great potential as a chemical thinner.

Free access

More peach [Prunus persica (L.) Batsch.] trees survived when planted in killed bahiagrass (Paspalum notatum Flugge `Paraguayan-22') sod growing between previous orchard tree rows (98%) than when planted in previous tree sites (81%) or in previous tree rows, but halfway between previous tree sites (79%). The previous orchard was removed Nov. 1986, and new trees were planted Feb. 1987. Surviving trees in the killed sod grew better than trees at the other two sites. Tilling the sites before planting did not affect nematode populations or tree survival and growth. Soaking the tree roots in a fenamiphos solution (1 g·liter-1) for 20 minutes before planting resulted in 79% tree survival vs. 93% survival for the nonsoaked trees. Fenamiphos sprayed under the trees at a rate of 11.2 kg·ha-1 during the spring and fall of the planting year did not change nematode populations, tree survival, or tree growth. The fenamiphos sprays reduced the increase in trunk cross-sectional area by 3 cm2 for trees in the sod. Other than leaf Zn concentration, which was low, concentrations of the elements were within the sufficiency range for Georgia for all treatments. Trees planted in the killed sod had an increased leaf K concentration and decreased leaf Mg concentration when compared with trees planted in the rows. Chemical name used: ethyl 3-methyl-4-(methylthio)phenyl (1-methylethyl)phosphoramidate (fenamiphos).

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Abstract

Horticulturalists frequently use the analysis of variance (F-test) to determine treatment differences. Many simple non-parametric tests, which require fewer assumptions, are also available. This note presents an example of the modified Friedman test as an alternative analysis for ranked data from a randomized complete-block design.

Open Access

Abstract

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.

Open Access

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).

Free access

Abstract

Rickettsia-like bacteria (RLB) are the presumptive cause of phony peach disease and are most numerous in peach (Prunus persica (L.) Batsch) roots. Of apparently healthy peach trees in a heavily infected orchard, 54% had RLB in root samples evaluated by 400 × phase contrast microscopy. Removing all peach trees with visible symptoms of phony peach disease would minimize the number of trees in the orchard infected with RLB. Of trees visibly infected with phony peach disease, 8% had root samples free of RLB on both sampling dates. Leaf concentrations of Mg and B varied significantly (P < 0.7%) with RLB levels in peach roots on 3 of 4 sampling dates. No element tested (P = 5%) separated roots free of RLB on two sampling dates from roots averaging 1 to 9 RLB per microscope field on one date and free of RLB on another date. RLB in peach roots preceded development of visible symptoms of phony peach and changes in leaf elemental concentrations. Soil analysis did not identify RLB infected tree roots (P = 5%).

Open Access

Abstract

The electrolytic, visual, and electrical impedance methods for estimating freezing injury were highly associated. The electrolytic method was more closely associated with the visual method and better separated the effects of freezing temperatures than did the electrical impedance method. The electrical impedance method yielded results in the shortest time. The electrical impedance and visual methods evaluated freezing injury to woody internodal stem sections without the need for unfrozen controls.

Open Access