Purple blotch of blackberry steam
1989
Arsenijevic, M. (Poljoprivredni fakultet, Novi Sad (Yugoslavia). Institut za zastitu bilja)
Purple blotch, a blackberry disease caused by the fungus Septocyta ruborum (Lib.) Petrak, gains economic importance in Yugoslavia. It develops on stems, first in the form of small spots (only a few millimeters in diameter) which are dark green, and then large spots (several centimeters long) which are purple, with a reddish ring and numerous pycnidia in the center. Pycnospores are colorless, straight or slightly curved, with 1 to 3 or, less frequently, with 4 septa, containing several oily drops. When relased from pycnidia, pycnospores infect blackberry stems while the foliage remains free of infection. The optimum temperature for the germination of pycnospores is 21-24'C, the minimum being 0'C and the maximum 33'C. Inoculation is difficult to induce. If the infection occurs at all, it takes place after a long incubation period lasting 2 to 8 months. The disease may be efficiently controlled by pruning and removing the infected stems as well as by treating blackberry bushes with copper -or carbamate- based preparations from the beginning of the growing season till the end of July, i.e., till the picking (Punithalingam, 1980).
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