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  • Author or Editor: W. Dozier x
  • Journal of the American Society for Horticultural Science x
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Abstract

Ethephon, (2-çhloroethyl)phosphonic acid, 3 was applied at rates of 125 ppm and higher to young apple trees in 3 greenhouse experiments. Leaf expansion and total number of leaves were reduced by ethephon; the effective concentration became lower as the growing season progressed. Leaf area on the primary shoot was reduced by 1,000 and 4,000 ppm ethephon, but was increased on the lateral branches by 4,000 ppm. Total leaf area was suppressed only by the 1,000 ppm treatment. Leaf necrosis occurred at 625 ppm and higher concentrations in 1 experiment. Lateral bud scales abscised and a proliferation of cells under the leaf scar occurred on trees treated with 7,500 and 10,000 ppm ethephon. Many lateral buds abscised on the lower two-thirds of trees treated with 10,000 ppm. Leaf abscission was induced by ethephon, and the higher concentrations caused earlier and more rapid leaf drop. The oldest leaves abscised first, and most leaves became somewhat chlorotic prior to abscission. Leaves apparently had to be of a certain physiological age before they could be induced to abscise.

Open Access

Abstract

Sprays of (2-chloroethyl)phosphonic acid (ethephon) 3 were applied to young apple trees in 2 greenhouse experiments. Ethephon suppressed terminal growth, internode length, and elongation of the pre-treatment stem. Ethephon applied at 4,000 ppm, 64 days after bud break resulted in abscission of some shoot apices. Lateral branching was induced by ethephon, but it was not dependent on abscission of the shoot apex. Whereas dry weight of the lateral branches was increased at 4,000 ppm, total stem dry weight was decreased by ethephon.

Open Access

Abstract

Concentrations up to 4000 ppm of (2-chloroethyl)phosphonic acid (ethephon) did not affect the net photosynthesis (Pn) of leaves on greenhouse grown apple trees. Leaf respiration was increased by 4000 ppm ethephon, but not by lower concn. Pn rates did not differ between cvs., but respiration of ‘Golden Delicious’ leaves was greater than that of ‘York’ leaves.

Open Access

Abstract

A combination of mechanical and hand pruning each year from 1971-1976 reduced pruning time over that of hand pruning alone for ‘Delicious’ apple (Malus domestica Borkh.). Yield was not significantly affected by pruning method with one exception in 1975. The use of the mechanical pruner destroyed the framework of the tree by inducing a thick canopy and reducing light penetration. Yield was increased by limb positioning at both the 2.3- and 3.0-m spacings. In 1974, higher yields were obtained with the 1.5-m spaced trees and in 1979 with the 3.0-m spaced trees. Average fruit weight was less for the 1.5-m spaced trees than for the 3.0-m spaced trees.

Open Access

Yields and economic returns above treatment variable costs were determined for young `Desirable' pecan [Carya illinoinensis (Wangenh.) C. Koch] trees grown for nine seasons under ten combinations of orchard floor management practice and irrigation. Orchard floor management practices were 1) no weed control, 2) mowed, 3) total weed control with herbicides, 4) grass control only with herbicides, or 5) disking, and trees were either irrigated or nonirrigated. Total weed control with herbicides increased cumulative yield through the ninth growing season by 358% compared to no weed control. In the humid environment where this experiment was conducted, irrigation did not increase crop value obtained from the young trees, except for 1 year. At the end of the ninth season, total weed control with herbicides was the only treatment to have a positive net present value. These data indicate that establishment costs for young `Desirable' pecan trees can be recovered as early as the eighth growing season if competition from weeds is totally eliminated.

Free access

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).

Free access

Abstract

Foliar and dormant shoot nutrient content and tree survival of ‘Loring’ and ‘Redhaven’ peach [Prunus persica (L.) Batsch] on 8 seedling rootstocks (Lovell, Halford, Harrow W-208, NA8, Nemagard, Siberian C, NC NRL-4, and NC 152-AI-2) were determined during 2 seasons. Foliar Ca levels of both ‘Loring’ and ‘Redhaven’ peach trees were lower on Siberian C rootstock than on any other rootstock in the study. Dormant stem Ca levels were lower when cultivars were on Siberian C rootstock than when on most other rootstocks. Cultivars on Siberian C had lower foliar K levels than most other scion/rootstock combinations. Some differences in foliar and stem N, P, Mg, and Mn levels were evident; however, these differences generally were small and inconsistent. After 6 years in the orchard, greatest tree loss occurred with ‘Loring’ on Siberian C and ‘Redhaven’ on Siberian C or NA-8. Other rootstocks did not affect tree survival of either cultivar. Tree width was smallest with Siberian C rootstock, but few differences in trunk circumference and tree height were observed.

Open Access

Estimates of long-term freeze-risk aid decisions regarding crop, cultivar, and rootstock selection, cultural management practices that promote cold hardiness, and methods of freeze protection. Citrus cold hardiness is mostly a function of air temperature, but historical weather records typically contain only daily maximum (Tmax) and minimum (Tmin) air temperatures. A mathematical model was developed that used Tmax and Tmin to estimate air temperature every hour during the diurnal cycle; a cold-hardiness index (CHI500) was calculated by summing the hours ≤10°C for the 500 h before each day; and the CHI500 was regressed against critical temperatures (Tc) that cause injury. The CHI500 was calculated from a weather station located within 0.1 km of an experimental grove and in the middle of the satsuma mandarin (Citrus unshiu Marc.) industry in southern Alabama. Calculation of CHI500 was verified by regressing a predicted CHI500 using Tmax and Tmin, to a measured CHI500 calculated using air temperatures measured every hour for 4 winter seasons (1999-2003). Predicted CHI500 was linearly related to measured CHI500 (r 2 = 0.982). However, the slope was a little low such that trees with a CHI500 = 400, near the maximum cold-hardiness level achieved in this study, had predicted Tc that was 0.5 °C lower than measured Tc. Predicted and measured Tc were similar for nonhardened trees (CHI500 = 0). The ability of predicted Tc to estimate freeze injury was determined in 18 winter seasons where freeze injury was recorded. During injurious freeze events, predicted Tc was higher than Tmin except for a freeze on 8 Mar. 1996. In some freezes where the difference in Tc and Tmin was <0.5 °C there were no visible injury symptoms. Injury by the freeze on 8 Mar. 1996 was due, in part, to abnormally rapid deacclimation because of defoliation by an earlier freeze on 4-6 Feb. the same year. A freeze rating scale was developed that related the difference in Tc and Tmin to the extent of injury. Severe freezes were characterized by tree death (Tc - Tmin > 3.0 °C), moderate freezes by foliage kill and some stem dieback (1.0 °C ≤ Tc - Tmin ≤ 3.0 °C), and slight freezes by slight to no visible leaf injury (Tc - Tmin < 1.0 °C). The model was applied to Tmax and Tmin recorded daily from 1948 through 2004 to estimate long-term freeze-risk for economically damaging freezes (severe and moderate freeze ratings). Economically damaging freezes occurred 1 out of 4 years in the 56-year study, although 8 of the 14 freeze years occurred in two clusters, the first 5 years in the 1960s and 1980s. Potential modification of freeze-risk using within-tree microsprinkler irrigation and more cold-hardy cultivars was discussed.

Free access

Abstract

Three rootstock—Elberta seedling (Elb), Lovell seedling (Lov), and Vila Fria seedling (VF)—were evaluated on an old peach-orchard site to determine their susceptibility to nematodes and their effect on growth, yield, survival, and foliar nutrient content of ‘Loring’ peach [Prunus persica (L.) Batsch]. During the first 6 years of the orchard's life, mortality rates of the trees were 18% (Elb), 21% (Lov), and 47% (VF). Rootstock did not affect tree height, spread, trunk circumference, or yield the first 3 crop years. However, Lov produced higher yields the 4th crop year and had a greater cumulative yield for the first 4 crop years than Elb or VF. When tree loss was taken into account, tree yield per hectare did not differ with Lov and Elb but was lower with VF. Rootstock did not affect nutrient level in the foliage. Nematode populations were low in the orchard and were unaffected by rootstock. Tree loss, yield differences, and cropping efficiency of trees on the different rootstock could not be accounted for by foliar nutrient levels, nematode populations, tree vigor, or size.

Open Access