2017 ASHS Annual Conference

Crop load management has grown increasingly important in recent years due to biennial tendencies, post-harvest disorders, and inconsistent fruit quality in apple production. This has been especially the case with new and valuable varieties like ‘Honey Crisp.’ Washington State University recently released a new cultivar named ‘Cosmic Crisp^TM’ that will be planted for the first time in 2017. Limited information is available about the productive characteristics of this cultivar, especially its tendency to be biennial. The main goal of this research is to optimize the crop load for this variety. Precision-based management techniques are on the rise. Proper crop load and leaf area assessments are needed to help guide the tree fruit industry, especially for new cultivars. An experimental trial evaluating the effect of crop load on fruit quality was conducted in 2016 on 39 ‘Cosmic Crisp^TM’ trees. Treatment combinations included trees trained to a Spindle system on Geneva-41 (G41) or M9 Nic-29 (Nic29) rootstocks and were pruned via a ‘Click’ or mechanical treatment. Three trees per rootstock, pruning, and crop load combination were selected, with no significant difference in Trunk Cross Sectional Area (TCSA). Four natural crop load range categories were identified (1.3, 2.5, 4.0 and 4.7 fruits/cm² of TCSA). Mechanical pruning significantly decreased the leaf area (LA) by 22% on average per tree when compared to the ‘Click’ treatment. Mechanically pruned trees exhibited a smaller leaf area:fruit ratio (LA:F) of 1009 cm²/fruit, whereas the ‘Click’ treatment had a LA:F of 1280 cm²/fruit. G41 had a significantly higher leaf area index (LAI) and LA:F per tree (1.64 and 1394 cm²/fruit) than Nic29 (1.12 and 914 cm²/fruit). G41 produced fruit with less overcolor and lower soluble solid content (SSC), and dry matter (DM). Crop load did not have a significant effect on LAI. However, crop load did have a significant impact on fruit quality in respect to weight, I_AD (chlorophyll/ripening index by DA meter), firmness , SSC, DM, and titratable acidity. Fruit quality was negatively influenced with increased crop load. Our study pointed out that a possible threshold for optimum fruit quality can be identified around 3 fruits/cm² of TCSA. Further data will be collected to confirm this preliminary result. Bienniality tendencies will be determined in the second year of the trial.