Damage. This disease affects the plant genus Prunus that includes ornamental species, plum, cherry, peach and apricot. Symptoms typically appear on the stem as a swollen area exuding a light brown gum (see Figure 15.18). The angle between branches is the most common site for the disease. Severe infections girdling the stems cause death of tissues above the infection, and the resulting brown foliage can resemble the damage caused by fireblight. In May and June, leaves may become
infected; dark brown leaf spots 2 mm across develop and the infected area may be blown out by heavy winds to give a ' shot-hole ' effect.
Life cycle and spread. The bacteria present in the cankers are mainly carried by wind-blown rain droplets, infecting leaf scars and pruning wounds in autumn and young developing leaves in summer.
Control. Preventative control involves the use of resistant rootstocks and scions, e.g. in plums. The careful cutting out of infected tissue followed by an application of paint and the use of autumn sprays of a copper compound (Bordeaux mixture), help reduce this disease.
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