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- Author or Editor: E. L. Proebsting Jr. x
Abstract
An accurate frost alert system is the first step in planning for frost protection. Forecasting methods are being updated by statistical studies from historical records at the fruit frost forecast stations. It is planned to put information in a computer at Yakima, Washington, which will permit retrieval of data for all past days with meteorological characteristics similar to the day of the forecast (7). Florida uses a regression-based model to relate forecast temp of 300 stations to actual forecasts for 15 key stations. Forecasts are updated at 10 pm based on new weather data and reports from growers on current conditions including extrapolations made with inexpensive net radiometer measurements (14, 23).
Abstract
As pomologists, our primary responsibility is to fruit trees growing in the frequently hostile environments which we insist on calling “fruit sites.” For most of the country the most consistently and effectively hostile element in a fruit tree’s environment is low temperature.
Abstract
There is need for rapid determination of cold resistance of plants in the field. Exotherm analysis was adapted to such needs for dormant fruit buds of peach (Prunus persica (L.) Batsch). Buds were excised with 1-2 mm of vascular tissue attached and then held near the thermocouple junction with an A1 foil wrap. Exotherms could be recorded from most of 25-30 buds per junction. Resolution was improved by slow rates of temperature decrease in the critical range (near l°/hour). At high rates of temperature decrease (8 to 15°/hour) buds were killed at higher temperatures. The distribution of bud mortality with temperature was very close to the standard skewed curve for buds evaluated by the tissue browning method.
Abstract
Trees of peach (Prunus persica (L.) Batsch) and pear (Pyrus communis L.) were grown without irrigation and received only 86-mm rainfall during the growing season. Many peach trees died after experiencing leaf water potentials below −30 bars in July and August. Defoliation began in July, fruit growth was arrested, flavor was astringent, and flower buds failed to differentiate. Pear trees survived under similar conditions although tops died back or grew poorly and flowering was reduced. Regrowth came from trunks and lower scaffolds. Heavy pruning (“dehorning”) delayed the appearance of drought symptoms until very late in the season and resulted in 100% survival of both peach and pear trees. Heavy thinning of peaches in early June did not affect current season's symptoms but apparently reduced dieback and death of trees.
Abstract
Severe frost injury was incurred about full swell on one group and about 4th leaf on another group of ‘Concord’ (Vitis labrusca L.) vines where sprinkling was interrupted during the night. The wet tissues were less cold resistant than dry tissues. Yield was reduced 22% by the early frost, 52% by the later frost. Bloom was delayed 10 days by the early frost, 18 days by the later frost. At harvest the berries were larger than non-frosted on the early-frosted vines and equal in size on the late-frosted vines. Color and soluble solids were lower on the frosted vines.
Abstract
(2-Chloroethyl)phosphonic acid (ethephon) applied Sept. 8, 1971 at 250 and 500 ppm delayed sweet cherry (Primus avium L.) bloom 3 to 5 days, thereby reducing spring freeze injury and increasing yield. Preliminary data from a nonfrost year indicate no deleterious effect of treatment on maturity or quality.
Abstract
The influence of ice nucleation-active (INA) bacteria on the susceptibility of flower buds (flowers or fruitlets) to frost injury in the field was determined during 6 years for five species of deciduous fruit trees. Frost analyses compared trees supporting either low [usually undetectable to 102 colony-forming units (CFU)/g] or high (104 to 108 CFU/g) populations of INA Pseudomonas syringae. Frequent sprays of streptomycin and oxytetracycline maintained low INA bacterial populations throughout the frost-tolerant prebloom and frost-sensitive postbloom stages. Despite contrasting INA bacterial populations of up to 106 CFU/g between the two treatments, there were no differences in mortality of flowers and fruitlets exposed to frosts with minimum air temperatures between −2.5° and −4°C. Measurements of yield and assessments of fruit quality, moreover, showed no effect of INA bacteria, corroborating springtime evaluations of mortality due to frosts. Mean ice nucleation temperatures (MNT) for flowers or fruitlets attached to 50-mm woody stems reflected their tendency to freeze at about −2°, regardless of the size of the INA bacterial population. In contrast, excised flowers or fruitlets carrying high populations of INA bacteria consistently exhibited an MNT 1° to 2° lower, demonstrating the governing influence of the intrinsic wood-associated ice nuclei during orchard frosts. Sources of ice nuclei associated with fruit trees and factors modifying their activity in orchards are discussed in relation to the feasibility of frost protection by controlling INA bacteria.
Abstract
Late summer sprays of (2-chloroethyl)phosphonic acid (ethephon) increased hardiness of dormant sweet cherry (Prunus avium L.) fruit buds, delayed bloom, and improved survival of spring frosts thus increasing yields. Wood hardiness was increased slightly. Autumn defoliation was sometimes hastened. Fruit size was reduced but color, soluble solids and firmness were not affected. Ethephon applied in late summer induced gumming of branches the following May in 1 year out of 6. Ethephon probably does not influence normal acclimation. Its effect is superimposed on the natural cycle.
Abstract
Succinic acid-2,2-dimethylhydrazide (daminozide) effectively retarded growth of vigorous young trees of sweet cherry (Prunus avium L.) if applied at rates above 4000 ppm and more than a month after bloom. It was relatively ineffective at 2000 ppm and within 2 weeks of bloom. Color, soluble solids, size and firmness of treated fruit were the same as on untreated fruit harvested 4 days later. Yield of ‘Bing’ was slightly increased. Daminozide induced “June” drop of ‘Bing’ and ‘Chinook’ and should be recognized as. a thinning agent on cherries. Treated cherries were more subject to post-harvest decay during 4 weeks’ storage at 0—2°C. Uniformity of color was increased slightly but significantly. There appeared to be no delerterious long-term effects of daminozide to sweet cherry trees.
Abstract
Cherries pitted prior to canning or treated with daminozide had lower drained weights, more total anthocyanin, more turbid syrup, darker Agtron red values, and were softer than nonpitted or nontreated cherries. USDA color grade was higher, but USDA character grade was reduced when cherries were pitted or treated with daminozide. CaCl2 applied as either a 3% dip prior to pitting or as a 1% addition to the syrup increased the firmness, decreased the turbidity of the syrup of pitted and nonpitted cherries, and reduced the number of split fruit in nonpitted cherries. CaCl2 improved the USDA character grade of pitted and nonpitted cherries, and daminozide-treated cherries. Delaying harvest by 8 days reduced drained weight losses, increased total anthocyanin content, pH and soluble solids, and resulted in a darker red canned cherry as measured by the Agtron. CaCl2 compensated for the reduced USDA scores for character caused by pitting or daminozide, increasing character to equal that of nonpitted or nontreated, respectively. Chemical names used: butanedioic acid mono(2,2-dimethylhydrazide) (Daminozide).