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Orchard Management


Several factors are key to ensuring apple trees can produce well and withstand harsh winters.


M


anagement practices during the growing season will assist in preparation for extreme rises and drops in temperatures as we have to deal with the oncoming impacts of climate change.


As I have said repeatedly in this column, crop thinning and crop volume start with pruning to a level that the trees can handle. By this I mean a crop level that not only will achieve 50 bins or more to the acre but also have good average size, with a harvest date that allows for maximum storage and quality factors. So, this means for a 50- bin crop of on a 2,500-tree-per-acre planting you will try to manage the trees to produce approximately 40 to 45 fruits per tree. Many more than this and fruit size may be compromised. By now the major efforts to manage crop volume, and inherent tree strength, pruning, spur pruning and chemical thinning are completed. The next steps are hand thinning and moisture management. Hand thinning helps in terms of final crop load to ensure that crop is reduced to preferably singles.


All winter seasons have the potential to be extreme and extremes may be severe — and I am not just referring to winter temperatures, but extreme summer heat as well. Too much fruit per tree might stress the trees and result in trees not having the ability to go into the winter with adequate reserves.


Crop and leaf balance are critical to fruit sizing and new fruit bud development, but this factor is also critical for tree moisture balance. If fruit numbers are not balanced by leaf number and in particular spur leaf size, fruit sizing will be compromised. In addition heat stress will take its toll on fruit size and quality if leaf and fruit are not in balance.


Essentially, I am starting to talk about tree vigour management. If there are too few fruits per tree with too much vigour, (i.e., too much moisture


20 British Columbia FRUIT GROWER • Summer 2014


By Peter Waterman Preparing properly for extremes


or a combination of water and too much nitrogen, colour may be delayed,


prompting the grower to


postpone harvest. On the flip side of this, the soil


must have adequate moisture going into winter; dry soils can encourage root damage from winter cold. This can easily happen with Fuji or any late variety. As a result, carbohydrate movement is delayed to the heavy branches, branch crotches, trunks and roots and will leave the trees shortchanged as they go into the winter.


There must be adequate moisture and nutrients to supply the crop. Nitrogen, potassium and boron need to move into the tree’s storage areas, not only for hardiness but for the bud start and bloom and fruit development the next season.


The variety of apple and the rootstock type also come into play, enabling trees to withstand more or less cold temperatures. Early maturing varieties such as Gala have more time for winter preparation, and there is more time for the grower to apply fall urea and boron sprays, as well to prep the spur leaves and next year’s fruit buds. There is considerable movement of nitrogen and boron applied to the leaves with fall applications and more time for multiple applications.


Blocks of different varieties are also influenced by rootstock. The selection made can influence tree size and vigour and there is some choice to have a more winter-hardy stock.


Malling 9 (in our area, most growers have used the selection T237) has moderately to good hardiness as M9 stops the scion growing relatively early in the fall, permitting increased early hardening off of the scion.


Bud 9 (Budagovsky 9 which results in a tree size between M 9 and M 26) is much hardier than M9. Ottawa 3 is also hardier than M9 or M26. Therefore, a combination of management practices and rootstock top combinations can make a difference in tree winter hardiness and orchard survival. Knowing the rootstocks makes a difference in how you might handle each variety and block.


— Retired orchardist and horticulturist Peter Waterman can be reached at


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