Dwarf cherry trees can suffer from a variety of diseases. Sources of diseases include fungi, bacteria, viruses and insects. Trees may be more susceptible when in a weakened state, or during overly wet periods. Dwarf cherry trees are susceptible to maladies such as brown rot, cherry leaf spot, and sour cherry yellow, to name a few.
One of the most common tree diseases, brown rot infects blossoms and causes dark spots on fruit. Two fungi cause brown rot: Monilinia laxa and Monilinia fructicola. Wind and water splash can spread these fungi that depend on wet weather. Tufts of grey or buff-coloured spores can cover a cherry tree. This fungus causes twig dieback, brown cankers on branches, and sometimes a brown, sticky gum. Cherries can mummify. Controls include pruning infected twigs to improve air circulation, and removing and destroying mummified cherries.
Cherry Leaf Spot
Cherry leaf spot harms the foliage by infecting leaves, and sometimes leaf stems, fruit stems and the fruit. The fungus Coccomyces hiemalis causes cherry leaf spot and appears as small, circular, purple spots that turn brown on a leaf's upper surface. Wind or water splash spread the fungal spores that thrive in humid conditions. Irregular dead areas can separate from healthy tissue and appear as holes. A leaf's underside can reveal the fungal spores at the centre of the spot that look like felt patches. Infected leaves turn yellow and drop. During an early spring infection, cherries may fail to mature.
Little cherry is a serious virus disease caused by little cherry virus 1 and little cherry virus 2. According to the British Columbia Government, Ministry of Agriculture and Lands, the apple mealy bug spreads virus 2 from tree to tree. Budding and grafting can also spread this virus. Trees infected for several years may appear less vigorous. Symptoms include smaller cherries with poor colour and flavour. Other problems include delays in ripening, and fruit maturing at different rates on the same branch. In the Lambert variety, for example, cherries measure half to two-thirds the normal size, with three flat sides and a dull red and pointed form. Trees can act as carriers of the virus without symptoms.
The fungus Podosphaera clandestine causes powdery mildew. Powdery mildew results in grey-white powdery spots on the underside of leaves. After the fungi over-winter on cherry trees, the windblown spores release during the wet, springtime weather. Poor air circulation contributes to the symptoms on the leaves of young shoots. A severe infection causes the leaves to turn yellow and distort. Fruit symptoms include spots that appear prior to the harvest.
Sour Cherry Yellow
The prune dwarf virus is the cause of sour cherry yellow. Symptoms include leaves that can take on a two-colour appearance with a yellow leaf and green veins. Infected leaves can drop off. Symptoms that develop on warm days and cold nights may include yellow rings, and mottling on leaves. Fruit production may also be reduced. The virus spreads by budding, grafting, seeds and pollen. Prune dwarf virus also affects sweet cherry trees.
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