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).
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.
Several aspects of hardiness behavior in ‘Bing’ cherry and ‘Elberta’ peach fruit buds were compared. Cherries averaged 2.1°C hardier than peaches. The difference was least in late fall and early spring, and greatest during winter. High temp caused the minimum hardiness level of peaches to rise by mid-winter; cherries not until late winter or early spring. Cherries hardened more rapidly than peaches during cold days. During dormancy cherry and peach buds hardened when temp was below -1.1 to -2.2°, dehardened when above that level. Hardening rates up to 1.9° per day for peaches and 2.8° for cherries were observed. Cherry buds hardened by cold days lost 6.1° of hardiness in 4 hr when exposed to 24°C.
Understanding of fruit bud hardiness in peach and cherry has progressed far enough that use of low temp control measures during winter, based on critical temp from laboratory evaluations, seems feasible.
As ‘Bing’ cherries (Prunus avium L.) matured, the quality characteristics changed rapidly but not consistently from year to year over 9 years. Color increased rapidly and at similar rates in all years. Soluble solids increased rapidly during years when the crop was light, but slowly when the crop was heavy. When crops were light, the fruit was full sized before color reached fresh market standards and there was no further growth as the fruit continued to mature. With heavy crops the fruit increased in size until they began to shrivel. Early in maturation the fruits were very firm, but they softened rapidly during the early fresh market stage, then more slowly.
Low temperature injury to flower buds of peach [Prunus persica (L.) Batsch.] and sweet cherry [Prunus avium L.] and to one-year-old shoots of peach and apricot (Prunus armeniaca L.) during fall and winter was more severe on trees treated with paclobutrazol (PP 333) than on those not treated. Paclobutrazol had no measurable effect on cold resistance of apricot buds or cherry shoots. The average date of 1st bloom was advanced by one to 2 days in all 3 species by paclobutrazol.
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.
Flower buds of 20 Prunus species representing 4 subgenera were collected during winter and spring of 1989-90. Buds were preconditioned at +3° or 7°C to test their minimum hardiness level (MHL) or the rate of hardiness increase. DTA revealed that most of the prunus species have flower primordia that supercool. The subgenus Padus have racemose inflorescences and do not deep supercool during dormancy. P. besseyi, P. nigra and P. americana had small exotherms between -22° and -27°C while P. davidiana and P. subhirtella had larger exotherms at higher temperatures. Exposure of flower buds to -7°C shifted LTES to lower temperatures and/or reduced the size of LTE, which became undetectable for many species including P. nigra and P. americana. P. davidiana and P. subhirtella increased hardiness by 6°/day at -7° while dormant. Deacclimation coincided with an increase in LTE50 and the development of xylem vessel elements in the bud axis, calyx and filaments as indicated by dye movenent. P. davidiana was the least hardy species and required only 700 chill units to satisfy the chilling requirement, while P. nigra and P. americana had LTE average of -26°C at MHL and required over 1000 chill unit accumulation.
The use of drip irrigation in orchards is increasing worldwide. Water shortage, prevention of ground water contamination, and improved production are the main reasons for this increase. The combination of partial wetting of the soil and control of the water penetration depth considerably increases the efficiency of irrigation. Recent technological improvements permit maintenance of a constant volume of irrigated soil in which gradients of soil water matric potentials and mineral concentrations exist from the irrigation point to the margins of the wetted zone. Because water and mineral uptake is a function of soil matric potential and mineral concentration, respectively, optimal uptake rates by certain portions of the root system always exist along these gradients for any given environmental conditions. Gradients of air concentration act similarly and permit maintenance of high water availability without any interference with root aeration. Due to the relative ability of the roots to exchange water, minerals, and, possibly, oxygen, the entire root system functions more efficiently compared to root systems under conventional irrigation methods. Physiological root restriction effects induce the formation of a large number of small roots with frequent branching. Consequently, the relative surface area for water and mineral absorption is increased several-fold, and the increased number of root tips that are known to be involved in production of hormones (such as gibberelins and cytokinins) is significant. Evidence for enhanced fruit bud formation under conditions of root restriction is presented here. Water treatment and filtration technology has improved, and clogging of surface or buried drip systems now can be minimized, which also increases the suitable range of water quality for use in drip systems.
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.
‘Bing’ cherries from lightly (LC) and heavily (HC) cropped trees were harvested at weekly intervals, subjected to impact damage (bruising), and stored at 4°C for up to 28 days in 1982 and 12 days in 1983. On a given harvest date, cherries from LC trees were firmer (higher bioyield) and riper, as indicated by higher soluble solids and total anthocyanin concentrations (TAcy) than those from HC trees. At a given color (TAcy) within the range of commercial shipping maturity, cherries from HC trees were more susceptible to bruising, were softer, and had lower concentrations of soluble solids, acid, and dry matter than cherries from LC trees.