Many of the apple cultivars desired for making hard cider are currently in short supply, a fact that has resulted in high prices for fruit of some especially desirable cultivars. Apple growers interested in producing cider apples may wish to top-work existing orchards so as to speed up production of high-demand cider apples. Top-working existing trees to cider apples rather than replanting with new trees has the following advantages:
- For many desired cultivars, trees ordered today may not be available for delivery until spring of 2017 or 2018 because tree fruit nurseries are increasingly producing trees to order and because some rootstocks are in short supply. Thus, it may take several years to acquire trees and several more years after they are planted before they begin bearing.
- Top-worked trees will grow more rapidly than newly planted trees and therefore can produce sizeable crops during the third year after top-working.
- If the orchard to be top-worked already has a tree support system, then top-working negates the need for installing a new tree support system.
- Most of the cultivars desired for making hard cider are either heirloom cultivars or old European cider apple cultivars, and they therefore are not protected by plant patents and propagation agreements.
Those wishing to top-work trees this spring should be gathering the necessary grafting wood sometime within the next four weeks. Grafting wood must be gathered as late as possible in winter but before the first warm days cause buds to swell. Methods for collecting and storing grafting wood and for top-working trees were described by Hoying et al. in an article published in New York Fruit Quarterly in spring of 2012.
Not all trees are appropriate for top-working. Poor results can be expected if the existing tree is already heavily colonized by xylem-inhabiting fungi. If there is a lot of discolored wood in the center of the trunk when the top of the tree is removed prior to top-working, that usually indicates that xylem-inhabiting fungi are present and may inhibit growth of the grafts. These fungi gradually colonize more of the wood (i.e.,the discoloration extends toward the bark) when trees are stressed, and removing the tops of the trees as required for grafting certainly creates stress for the trunk and root system. As these xylem-inhabiting fungi advance toward the bark, they can cause trees to decline (Fig. 1, below). A completely healthy apple tree has no dark-colored xylem when viewed in cross section because apple trees do not form heartwood like oaks and many other tree species. Thus, a completely healthy tree will have completely white wood when a large limb or the top of the tree is removed (Fig. 2). However, it is very rare to find trees that are completely free of xylem inhabiting fungi. The presence of some darkened xylem in the center of a trunk is not a problem so long as there is roughly an inch or more of healthy white xylem beneath the bark all the way around the trunk (Fig. 3). However, if discolored xylem (i.e., darkened wood) is present within an inch of the bark, then the fungi in that wood will often colonize the remaining wood fairly rapidly after the top is removed and the top-worked trees will often develop bark cankers that may kill or weaken the grafts.
For more information on how xylem-inhabiting fungi invade trees and contribute to cankers and tree decline in apples, see the 2007 article “Canker Problems in Apple Orchards” that I published in the New York Fruit Quarterly in 2007.
- Finally, it is worth noting that many heirloom cultivars and European cider apple cultivars are extremely susceptible to fire blight. Special care will be required to prevent fire blight from infecting blossoms that develop on any grafted trees. Some of the European cider apples are especially problematic because they bloom much later than our common apple cultivars, thereby increasing the likelihood that bloom will occur during warm weather favorable for blossom blight. The late bloom also means that streptomycin sprays needed to control blight will be forgotten because farmers will be focused on fruit thinning sprays for their other cultivars. On farms where there was a lot of fire blight last year, it may be unwise to top-work trees to cider apple cultivars if adjacent ungrafted trees were blighted last year and are therefore likely to carry inoculum into the coming season.