Climate change, and specifically global temperature increase, is expected to alter plant phenology. Temperate deciduous fruit trees have cultivar-specific chill and heat requirements to break dormancy and bloom. In this study, we aimed to estimate chill and heat requirements (in chill portions, CP, and growing degree hours, GDH, respectively) of 25 almond (30–36 years) and 12 apple (14–26 years) cultivars grown under a Mediterranean climate. The set included early and late blooming genotypes. Long-term phenological and temperature records were analyzed by means of partial least squares (PLS) regression. The main difference between early and late genotypes was chill requirement, ranging from 8.40 CP of early genotypes to 55.41 CP of extra-late genotypes. However, as chill requirements are quite easily attained by all almond cultivars in this study, year-to-year variations in actual blooming dates for each genotype are governed by variability of mean forcing temperatures. In contrast, different chill and heat combinations resulted in similar mean blooming dates for the studied apple cultivars. Mean temperature in both chilling and forcing phases determined their blooming time in the location studied. Overlaps and gaps between both phases were obtained. Despite some limitations, the PLS analysis has proven to be a useful tool to define both chilling and forcing phases. Nevertheless, since the delineation of these phases determine the total amount of CP and GDH, further efforts are needed to investigate the transition of these phases.

Fruit thinning is the most important yet difficult practice that drives orchard profitability. High labor costs and difficulty to improve return bloom by hand thinning have left chemical thinning as the main method used by growers. However, unpredictability and safety/environment concerns regarding chemical thinning have set mechanical thinning as a sound alternative. Thirteen field experiments were performed during 2004-2016 in order to evaluate several agents for their use as new thinners, and adjust mechanical thinning on 'Gala', 'Golden Delicious' and 'Fuji'. Olive oil applied at bloom reduced crop load, but russetting was also increased. Therefore, while their use is not advisable for russetting prone cultivars such as 'Golden Delicious', it could be a good thinner for cultivars like 'Red Delicious'. Lime sulfur did not have a consistent thinning effect in our study when applied at bloom. Overall, no differences regarding economic value between hand, chemical, and mechanical blossom thinning were observed, suggesting mechanical thinning as a valid alternative approach. For 'Gala' strains, 6 km•h-1 and 250 rpm with 270 strings was the best configuration to provide an ideal crop load of ~6 fruit/cm 2 of TCSA and an average fruit size of 170 g. For 'Fuji', 5 km•h-1 and 320 rpm with 270 strings provided a crop load in accordance to the optimum range for this cultivar in our conditions. However, combination of mechanical thinning plus chemical treatments might be the ideal strategy for 'Fuji' strains when the initial number of flower clusters per tree is above 500. For 'Golden Delicious' strains, 6 km•h-1 and 230 rpm with 270 strings was the best configuration to provide an ideal crop load within the optimum range. Mechanical thinning timing was also examined at different phenological stages (E2, F1, F2, and G), with no significant differences regarding yield, fruit size or crop load between them. Two prediction models ('Gala' & 'Golden Delicious') were developed to adjust the right tractor and rotational speeds depending on the initial number of flower clusters. The method begins with first calculating the final fruit number needed per tree (crop load for each particular cultivar) in order to achieve the desired yield. Then, tractor and rotational speeds can be determined by the model once knowing the initial number of flower clusters per tree.

Thinning is an important technique in apple growing which is used to reduce the number of fruits per plant and achieve commercial fruit size and quality. The objective of this work was to evaluate the efficacy of one and two applications of the chemical thinner Brevis in Gala apple applied at different fruit sizes and at different intervals between the first and second spray. The trials were conducted over two seasons from 2015 to 2016 in apple orchards of the IRTA experimental agricultural stations of Mas Badia and Lleida (Spain).One or two applications with Brevis were applied at different fruit sizes (king fruit diameter ranging between 7.5 and 13.5 mm) and at a rate of 1.65 kg/ha for all treatments. Under the trial conditions, a Brevis thinning effect was observed in all trials with a reduction in crop load, fruit set and number of fruits per tree which varied according to the number of applications. In addition, average fruit weight, color and diameter increased significantly with treatments in which Brevis reduced the number of fruits per tree. The degree of abscission of Brevis was highly dependent on night temperature and, for this reason, there was a high degree of variability between trials in terms of efficacy. Our results show that the number of days between applications was not as important a factor for Brevis efficacy as the difference in night temperature in the days immediately after its application.

No abstract

Hail nets reduce photosynthetically active radiation (PAR) and alter the environment under the netting in apple orchards. Thus, we investigated the effect of nets on the efficacy of metamitron, a short-term photosynthesis inhibitor used for fruit thinning. The objective of this study was to evaluate the effect of the netting and metamitron on thinning efficacy, yield, fruit quality and chlorophyll fluorescence in three apple cultivars. One or two metamitron applications at 165, 248 and 330 g (ai)/ha were applied the tree under different colored nets. The reduction of PAR was highest with black nets (19%-22%), followed by green (13%-15%) and white nets (6%-11%). There were no significant differences (P>0.05) in fruit weight or size with or without nets. Double applications of metamitron increased average fruit fresh weight and reduced the fruit set over four experiments. In contrast, single applications were less effective. In two experiments, thinning was associated with lower yields. However, there was no effect in the other two experiments.The double treatments tended to increase the percentage of the crop with fruit larger than 70 mm in diameter. All thinning strategies showed similar inhibition in fluorescence, with the only observed significant differences between treatments occurring when using a single or double application. The results show that netting does not affect the response to thinning with metamitron.