Abstract
An experiment in thinning kiwifruit (Actinidia deliciosa Planch.) vines at the bud swell stage vs. at fruit set stage was conducted in the Western Galilee to a) determine the optimal physiological stage of thinning, b) optimize fruit weight and yield, and c) determine the relationship between fruit number per vine and alternate bearing. A negative relationship was found between the number of fruits per vine and fruit weight or alternate bearing. Vines thinned at the bud swell stage always carried larger fruits than those thinned after fruit setting. As the fruit load on the vine decreased, smaller differences were observed between the two thinning dates. Assuming that individual fruit weight should not be < 70 g, thinning at the bud swell stage allows a yield of 1700 fruits per vine, and that at the fruit-set stage only 1400 fruits per vine. Vines not sprayed with Alzodef (H2CN2, cyanamide) to break dormancy yielded less than half the number of fruits as the sprayed vines.
fruit firmness and the content of sugar and acid in the berries, primarily as a result of a slightly smaller berry size. Cropping thinning is also an effective strategy for dealing with soil water limitations in a number of fruit crops. For example
A tank mix of fish oil plus liquid lime sulfur has proven to be an effective chemical thinner for apples in the bloom and postbloom periods. This combination was labeled for use as a chemical thinner in Washington State in 2003. There are several concerns with fish oil when used in this thinning mixture. Phytotoxicity is one concern. Apple growers have a reluctance to utilize this oil because of its expense and repulsive odor. Research to date has been conducted using oil from a single small source in Washington State. Shipping fish oil across the country is expensive and the consistency and purity of fish oil from other sources is unknown. Fish oil may function as a surfactant and penetrant, and it may also have a direct thinning effect. The objective of these studies was to evaluate the efficacy of several surfactants and oils in combination with lime sulfur for thinning apples. Lime sulfur has been less effective as a thinner when used alone than when used with oil in our studies. Regulaid, LI-700, and Silwet L-77 were shown to be less effective than oils for achieving thinning. Vegetable oil has been very effective in the thinning combination, while petroleum oils have been effective in some eastern U.S. trials, but less effective in the west. Tank mixing fish oil with lime sulfur has remained among the best treatments in our trials, while vegetable oil also shows promise.
Applications of soybean oil to dormant peach [Prunus persica (L.) Batsch] trees were tested for prebloom thinning of flower buds in five separate experiments. Data were combined from experiments in which 2.5% to 20% emulsified soybean oil was sprayed on `Belle of Georgia' or `Redhaven' trees. The number of dead flower buds was concentration-dependent with maximum bud kill of 53% occurring with application of 12% soybean oil. The amount of thinning was fairly consistent from year to year, ranging from 34% to 51% when 10% soybean oil was applied, but was less consistent when 5% was applied, ranging from 6% to 40%. Overthinning by midwinter applications of soybean oil occurred in one experiment when bud mortality on nontreated trees was 40% due to natural causes. Mild to moderate spring freezes occurred in three experiments, but did not reduce yield more in soybean oil–thinned than in nontreated trees. Flower bud survival was improved when trees were sprayed with 10% or 12% soybean oil prior to a –4 °C spring frost. Applications of soybean oil to dormant trees thinned flower buds, reduced the amount of hand thinning required, and hastened fruit maturity.
Influence of prebloom and full bloom applications of hydrogen cyanamide on `Simka' and `Friar' plums in Southwest Idaho and `Florda Prince' peach in Southwest Arizona was studied. Prebloom application of 0.5% hydrogen cyanamide caused severe toxicity to the fruit buds in `Friar' lure, while 2% hydrogen cyanamide did not cause toxicity in `Simka' plum. `Simka' fruit was effectively thinned with 1-2% prebloom application. At full bloom, 1.5% hydrogen cyanamide caused severe flower and leaf burning in both `Friar' and `Simka' plums, while concentrations between 0.1% and 1% thinned flowers (fruits) in both of the plum cultivars. Influence of hydrogen cyanamide on final fruit set, fruit size and maturity are also studied. Prebloom or full bloom applications of 2% or 3% hydrogen cyanamide eliminated 95 to 100% of the blooms, while application of this chemical at 1% sufficiently thinned the fruit. Number of commercially packed large peaches in trees receiving 1% hydrogen cyanamide was the same as that in trees thinned by hand, suggesting hydrogen cyanamide as a potential chemical for stone fruit thinning.
Release LC (Abbott Laboratories), a commercial formulation of gibberellins, was applied to apricot, cling peach, freestone peach, nectarine, and plum varieties. Application was by commercial airblast sprayer. Fruit firmness was increased in the season of application in all crops. Meta analysis of the data indicated a maximum response for each crop differed over the rate range of 16 to 48 g a.i./acre. Changes in fruit soluble solids were slight. No differences in fruit color were observed. Reduction in flower bud density (thinning) was observed the following season. The reduction in bud density reduced the time required to hand-thin to a commercially acceptable level. A difference in thinning sensitivity to gibberellin was evident between crops.
Abstract
Five-year-old ‘Riesling’ grape (Vitis vinifera) vines growing in the Okanagan Valley of British Columbia were subjected to three crop levels (full crop, two clusters per shoot, and one cluster per shoot) in combination with no shoot thinning or thinning to 24 shoots per meter of row. Reduction in crop level improved vine size and cane periderm formation slightly. Yield per vine was linearly related to crop level, but berry weight, berries per cluster, and cluster weight increased with decreasing crop level. °Brix and pH increased and titratable acidity decreased with reduction in crop level. Thinning to 24 shoots per meter of row provided some improvement in yield components and °Brix. Crop loads below 10 kg of fruit per kilogram of cane prunings are necessary to achieve adequate fruit maturity under Okanagan conditions.
Abstract
Vydate (oxamyl; methyl N’, N’ dimethyl-N[methylcarbamoyl) oxy]-l-thioox-amimidate) and Sevin (carbaryl; 1 napthyl-N-methyl carbamate) did not give significant thinning of ‘Starkrimson Delicious’ apples (Malus domestica Borkh.) when applied as airblast treatments in 3 years of tests. Neither multiple applications nor the addition of a 70-sec superior spray oil gave significant thinning compared to untreated controls. Airblast treatments of these materials on ‘Golden Delicious’ were effective but were inadequate to reduce crop load to the desired level. The data suggest that Vydate and Sevin are inadequate as thinners if applied with airblast machines. Ethephon treatments caused erratic responses at the rates and timings used. Sevin applied for thinning caused an increase of European red mites and their eggs.
Various rates of Wilthin were applied at full bloom to limbs carrying 150 to 250 flowers to study their activity on blossom thinning of `Loadel' peaches. Wilthin applied at 0.75% and 1.0% significantly reduced fruit set to 29% and 30%, respectively, while the control produced 94%. The effectiveness of the 0.75% rate was dramatic, but it is interesting to note that the 1.0% rate did not lead to excessive thinning nor phytotoxicity on foliage or fruit. More extensive studies need to be done to fully determine the potential of this material. However, these results suggest that further testing of Wilthin on a larger scale is warranted.
Abstract
In British Columbia, ‘Bartlett’ pears are thinned with naphthaleneacetamide (NAAm) applied by gun application at 10 μg-liter (w/v) or with air-blast sprayers at 44 g a.i.ha-1, between 13 and 21 days after full bloom. Concern has been expressed by packinghouse personnel about the storage quality of these pears. Higher incidences of breakdown have been suggested, and no controlled experiments have been reported to substantiate or refute such claims. Therefore, a study was conducted during 1980-1983 to assess several quality parameters of ‘Bartlett’ pears thinned by hand and with NAAm.