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AVG sprays applied to `Redhaven' peach (Prunus persica L. Batsch) trees 53, 72, 80, 87, or 94 days after full bloom (AFB) slightly delayed the first harvest date. Applications at 53 or 94 days AFB slightly delayed cumulative second and third harvests. The fourth (final) harvest was not delayed by any AVG spray. Firm commercial-harvest peach and nectarine fruit submerged for 60 s in AVG solutions softened more slowly than the controls when kept at room temperature (≈24 °C) for 3 to 12 days. AVG-treated fruit dipped in ethephon after 4 days showed an increased rate of softening compared to fruits treated only with AVG. Fruit submerged in AVG solutions and stored at 1.5 or 4.5 °C for 12 to 18 days did not differ in firmness from the controls upon removal from cold storage but sometimes softened more slowly after storage. Ethylene evolution from AVG-dipped fruit was not measureable even after it was kept at room temperature for 12 days. Chemicals used: Aminoethoxyvinylglycine hydrochloride (AVG); 2-chloroethylphosphonic acid (ethephon).
Ethephon applied 12 to 26 days after full bloom at 1000 to 1500 mg·liter-1 not only substantially inhibited apple (Malus domestia Borkh., spur `Delicious' strains) tree growth but also caused fruit abscission. Gibberellin plus ethephon did not prevent fruit abscission when ethephon was used at these rates. Several low weekly doses of ethephon controlled tree growth without causing fruit abscission. Ethephon increased fruit soluble solids concentration and substantially reduced fruit starch in the application year. Ethephon greatly increased flowering and fruit set the following season. Fruit length: diameter ratio was not altered by the previous seasons' low weekly doses of ethephon. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).
AVG applied 2 to 6 weeks before the optimum harvest date for several cultivars dramatically reduced pre-harvest fruit drop. The loss of fruit firmness and starch loss after the optimum harvest date was reduced by AVG sprays. The development of watercore in `Starkrimson Delicious' and `York' and maturity cracking in `Rome' and `Golden Delicious' were delayed and/or prevented by AVG. Color development was slightly delayed for most red cultivars and `Golden Delicious'. Soluble solids concentration was generally unchanged. Airblast applications of 123 g·ha–1 AVG was no more effective than a standard rate of NAA (28 to 56 g·ha–1), but rates of 248 g·ha–1 AVG and above were more effective than NAA for most cultivars. When fruit were left on the tree for periods of 3 to 5 weeks after the optimum harvest date, NAA hastened the loss of fruit firmness and starch and NAA increased watercore of `Delicious' and maturity cracking of `Golden Delicious' and `Law Rome'. Soluble solids and red color were generally unaffected by NAA. Ethephon sprays hastened the rate of fruit drop. When NAA was tank mixed with ethephon, NAA delayed fruit drop caused by ethephon, but AVG did not. The use of superior oil or Regulaid surfactant did not affect NAA or AVG responses; however, the silicone surfactant Silwet L-77, in one experiment, promoted the effectiveness of AVG. Tank mixing NAA or AVG with pesticides (Guthion + Lannate + Captan) did not affect the responses of AVG or NAA on fruit drop.
Several classes of chemicals (auxins, cytokinins, gibberellins, ethylene releasing compounds, photosynthetic inhibitors, pollination inhibitors, and carbamates) have been found effective for reducing fruit numbers on apple and/or peach trees. The selection of a chemical for use as a commercial thinner is usually based on consistent effectiveness, freeness from fruit, leaf or tree injury, increases in fruit size, and low degree of environmental influences on fruit thinning or injury. In recent years research has been curtailed on newer chemicals due to the small and unique market, the costs of chemical registration, and non-support of the chemical industry due to potential law suits from over or under thinning. Recommendations that include the use of combinations, adjuvants or timings inconsistent with the existing label will likely become more difficult than in the past. Our results with Wilthin, YI1066, MYX6121, endothall and ammonium thiosulfate have been very positive as bloom thinners for peach. Further research is needed to determine which of these have the least injury for apples. In addition, we have considerable interest in Oxamyl and 6-benzyladenine for thinning apple fruit and their combinations with existing thinners and adjuvants.
Ethephon application at rates of 1000 ppm to 1500 ppm substantially inhibited tree growth but also caused fruit abscission. Application of gibberellin plus ethephon did not prevent fruit abscission. Low weekly doses of ethephon did not cause fruit abscission but gave good control of tree growth. Ethephon increased soluble solids and substantially reduced starch in the year of application. Flowering and fruit set were greatly increased by ethephon sprays the previous season. Fruit diameter or length:diameter ratios (L/D ratio) were not altered by the previous seasons' low weekly doses of ethephon.
Complete or partial loss of fruit in high density apple plantings can result in excessive shoot growth that is normally controlled by cropping. Spot spraying with ethephon in the top part of `Redchief Delicious'/MM. 26 trees for tree training purposes increased the number of shoots over 10 cm in the lower part of the tree, but also caused fruit abscission in the unsprayed parts of the tree. Summer training of high density plantings of fireblight susceptible varieties with spot sprays of ethephon would reduce the need for cutting or pinching branches during the tree growth period.
When temperatures reach -26 °C and lower, even for brief periods of time, damage to fruit buds and woody tissue of the peach tree is common. Low temperature injury on peach can lead to bark damage, gummosis, increased incidence of perennial canker, partial or complete crop losses, reduced shoot growth and/or tree death. In Jan. 1994 the Eastern Panhandle of West Virginia and surrounding states experienced three successive nights of temperatures at -28 °C or lower. Beginning in Apr. 1994, 7-year-old `Blake'/Lovell peach trees were subjected to four pruning levels (none, light, heavy, and dehorned) each at three times (April, May, and June) in a replicated factorial arrangement. Specific pruning treatments were applied only in 1994; a local commercially recommended level and time of pruning were applied to all trees from 1995 through 1998. Treatments had a significant effect on canopy volume and fruit yields. Trees receiving no pruning or dehorned trees and trees pruned in June had lower yields in 1995 than trees pruned in April or May or trees receiving a light or heavy pruning. These treatments also produced fewer large fruit at harvest. Lower yields and smaller fruit led to reduced dollar returns per hectare in 1995. Yields from 1996 through 1998 were lower for trees that were dehorned pruned in 1994 although there were little or no differences in fruit sizes between treatments. Time and/or level of pruning had effects on the number of cankers and number of large (>5.1 cm) cankers.
Abstract
Several methods were evaluated for inducing apple (Malus domestica Borkh.) fruit abscission before the harvest season. Pedicels abscised within 7 days after being defruited, but drop inhibitors retarded abscission minimally. Injecting ethephon into the seed cavity induced only 70% to 80% fruit drop within 13 days after treatment. Removing the calyx half of a fruit (half-fruit) induced abscission within 13 days of treatment, and half-fruit responded to drop inhibitors. Scoring branches before treatment did not influence abscission of half-fruit, but increased the severity of phytotoxic symptoms caused by triclopyr and dicamba. The half-fruit method facilitates the screening of many potential drop inhibitors because treatments can be applied to single-limb-units at any time during the growing season.
Peach trees [Prunus persica (L.) BatSch.] blossom-thinned by hand were overthinned due to poor fruit set of the remaining flowers; however, their yield was equivalent to trees hand-thinned 38 or 68 days after full bloom (AFB). Blossom-thinned trees had three times the number of flower buds per unit length of shoot and had more than two times the percentage of live buds after a March freeze that had occurred at early bud swell the following spring. Blossom-thinned trees were more vigorous; their pruning weight increased 45%. For blossom-thinned trees, the number of flowers per square centimeter limb cross-sectional area (CSA) was two times that of hand-thinned trees and four times that of the control trees for the next season. Fruit set of blossom-thinned trees was increased four times. Flower buds on the bottom half of shoots on blossom-thinned trees were more cold tolerant than when hand-thinned 68 days AFB. Fruit set per square centimeter limb CSA was 400% greater the following year on blossom-thinned trees compared to controls. Removing strong upright shoots on scaffold limbs and at renewal points early in their development decreased dormant pruning time and weight and increased red pigmentation of fruit at the second picking. The number of flower buds per unit shoot length and percent live buds after the spring freeze were negatively related to crop density the previous season for trees that had been hand-thinned to varying crop densities at 48 days AFB. According to these results, blossom thinning and fruit thinning to moderate crop densities can influence the cold tolerance of peach flower buds in late winter.
Seven-year-old `Blake'/`Lovell' peach [Prunus persica (L.) Batsch] trees were subjected to four pruning levels (none, light, heavy, and dehorned) each at three times (April, May, and June) in a factorial arrangement following freezing injury in January 1994. Pruning had a significant effect on canopy height, canopy volume and fruit yields. Peach trees pruned in April or dehorned (severe pruning) had less canopy volume in the first fruiting season (1995) after the pruning treatments were initiated than trees pruned in May or June and light or heavy pruned trees. In 1995, yields were lower for trees pruned in June, nonpruned or dehorned trees in 1994. These treatments also produced fewer large fruit at harvest and thus reduced dollar returns per hectare in 1995. In 1996, fruit numbers and fruit sizes did not differ among treatments, but dehorned trees had lower returns per hectare because trees were smaller. The results of this study indicate that peach trees subjected to moderate winter injury should be pruned no later than 2 to 3 weeks after bloom using a heavy level of pruning. There appears to be no economic advantage to dehorn pruning even though canopy volume can be reduced resulting in a smallertree with high quality wood. The results clearly illustrate the long-term negative effect of dehorn pruning on yields resulting from reduced canopy volume. Mean number of cankers per tree increased over time from 1995 through 1998, but pruning treatments did not affect the number of cankers produced. Pruning treatments did affect the size of cankers and the number with visible gumming.