Answer: Unfortunately, in order to remain healthy, most apple trees need to be on a regular spray schedule. If your trees are developing calluses or growths on the trunks and branches, they may have developed a disease called scab. The fruits will have lesions on them and the foliage will develop olive-green splotches before turning brown. If you noticed these problems with the fruit and foliage, it's likely your trees have scab. You can avoid the problem in the future by using a lime-sulfur (Bordeaux) as directed on the label. If you did not notice these symptoms on the foliage and fruit, then your tree may be showing signs of mechanical damage (lawn mower, weed whacker, etc.) If this is the case, the wounds will heal over (creating a callus) and there's no other treatment required other than keeping lawn equipment a safe distance away.
If you decide to replace your trees, the most disease resistant columnar apple trees are Golden Sentinel and Scarlet Sentinel. Golden Sentinel produces a striking display of white spring flowers followed by very large and attactive solid golden yellow fruit. Sweet, juicy and delicious. Disease resistant and productive. Scarlet Sentinel has large, delicious, greenish-yellow fruit with an attractive red blush. Dense clusters of white flowers are followed by abundant, closely spaced fruit. Very productive and disease resistant and non-branching. It's the most dwarfing of the Columnar varieties.
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