Mario Miranda Sazo, Fruit Specialist, Cornell Cooperative Extension, Lake Ontario Fruit Program
Terence Robinson, Professor, School of Integrative Plant Science Horticulture Section Cornell AgriTech
When pruning a Honeycrisp block without knowing the floral bud percentage (% of floral buds in a 100 bud sample of spurs from randomly selected shoots in a Honeycrisp block), you are risking removing too many of the flower buds if return bloom is low. If the previous crop load was too high then flower bud numbers will likely be below or close to the target number and pruning is likely to remove too many. Floral bud identification at the dormant stage is not easy without dissecting buds and viewing them under a microscope. It can only be accomplished by a professional lab or by a trained grower and/or employee. For this reason, it is helpful to delay pruning until the spring. We suggest that annual bearing varieties (Gala, McIntosh, Empire, NY-1, etc.) be pruned first and the biennial bearing varieties last. There is a 3-4 week window from green tip to bloom when it is easy to identify and count flower buds per tree and then prune to the target flower cluster number at that time.
However, many growers who have significant acreages of Honeycrisp (or other biennial bearing varieties) cannot wait to prune all of their trees in the spring. If you must begin pruning biennial varieties during the winter, we suggest two approaches you could consider.
- Before pruning determine the number of flower buds per tree by sampling 10 branches (3/4-1 inch in diameter) from 5 representative trees in the orchard and dissecting all the spurs on the branches and examining the dissected buds under a microscope to determine what percentage of the spurs are floral. Then, adjust pruning intensity to ensure that the target number of flower buds are left on the tree. Few growers are prepared or trained to sample branches, dissect, and examine buds with a microscope.
To help growers with this task, see the below article. You can also view our video on precision pruning here: https://www.youtube.com/watch?v=29cF8yOKup0&t=190s
- Another approach is to lightly prune Honeycrisp during the winter by only removing 1-3 large limbs (remember to always leave a longer stub with Honeycrisp, 2-3 fingers length to secure shoot renewal). Then between green tip and full bloom ‘touch up’ the trees which have too many flower buds by removing additional whole limbs and by spur pruning.
Lastly, we remind growers that to avoid biennial bearing of biennial varieties and to improve fruit size of annual varieties, precision pruning is essential. We suggest counting the total number of flower buds on 5 representative trees and then through pruning the removal of extra flower buds leaving a precise number of buds. To accomplish this the first step of precision pruning is to determine the target number of final fruits at harvest which is a function of desired fruit size, yield and the potential of the trees. Secondly, calculate the number of buds to leave based on the recommended but load and thirdly, adjust the number of buds to be left after pruning by the percentage of buds that are floral. The following is an example of a final fruit number target and the calculated spur number to leave after pruning on Tall Spindle Honeycrisp trees planted at 3X11 ft. spacing (1320 trees/acre).
Target yield = 900 bu/ac * target fruit size (72 count @260gr) / tree planting density (1,320 trees/acre) = 50 fruits /tree. Remember we suggest leaving a few extra flower buds as insurance against frost or poor set. Based on the most recent Cornell Honeycrisp pruning research we are currently suggesting that growers leave 80% more flower buds than the target fruit number as insurance. In the example where we need 50 final fruits/tree we suggest increasing that number by 1.8 = 90 flowering spurs. Lastly, if only 50% of the spurs are floral then the number of spurs to leave after pruning would be double that number (180 spurs). The table below gives bud load factors and target final flowering spur numbers for annual and biennial bearing cultivars.
