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Disease Note.

First Report of Septoria Leaf Spot of Pistachio in Arizona.. D. J. Young, Cooperative Extension, University of Arizona, Tucson 85721. T. J. Michailides, Department of Plant Pathology, University of California, Berkeley, Kearney Agricultural Center, Parlier 93648. Plant Dis. 73:775. Accepted for publication 14 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0775E.

Since 1986, a moderate leaf spot caused by Septoria pistaciarum Caracc. has been observed on leaves of pistachio (Pistacia vera L.) cultivars Kerman (female) and Peters (male) during the rainy season (July through September) in southeastern Arizona. Symptoms were observed only during wet weather. Leaf spots from natural infections were round to irregular and 1-2 mm in diameter, with one to 20 pycnidia per lesion. Pycnidia measured 60-108 !lm in diameter; conidia from pycnidia on leaves were hyaline, curved to falcate, and 44-85.4 × 3-3.9 µm, with three to nine septa. A survey in September 1988 of disease incidence throughout the pistachio-growing area (approximately 800 ha in southeastern Arizona) indicated that the disease is widespread on P. vera leaves but not on those of P. atlantica Desf. and P. terebinthus L. Although Septoria leaf diseases of pistachio have frequently caused defoliation of trees in Mediterranean countries (1), pistachio trees in Arizona did not defoliate. The disease was reported for the first time in the United States in Texas in 1971 (2).

References: (1) A. Chitzandis. Ann. Inst. Phytopathol. Benaki 10:29, 1956. (2) J. L. Mass et al. Plant Dis. Rep. 55:72, 1971.