VIEW ARTICLE

Physiology and Biochemistry

Nutritional Diseases of Pistachio Trees: Potassium and Phosphorus Deficiencies and Chloride and Boron Toxicities. L. J. Ashworth, Jr., Plant pathologist, Plant Pathology Dept., University of California, Berkeley 94720; S. A. Gaona(2), and E. Surber(3). (2)(3)Blackwell Management Company, P. O. Box 2393, Bakersfield, CA 93303. Phytopathology 75:1084-1091. Accepted for publication 6 May 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-1084.

Potassium (K) and phosphorus (P) deficiencies accounted for unthriftiness and poor yields of pistachio trees. K-deficient trees had sparse foliage canopies, small leaves without chlorosis, and pronounced shoot dieback. The threshold K level of leaves for deficiency appeared to be 0.7- 0.9% in midsummer. P-deficient trees had normal dense foliage canopies, normal-sized leaves, and leaf chlorosis. Chlorosis of P-deficient trees appeared first on leaves terminal to nut clusters but later involved part or all foliage of the affected trees. Chlorosis was first interveinal, but leaves later became bright yellow, desiccated, and dehisced prematurely. The threshold P level for deficiency appeared to be 0.09- 0.1%. Vegetative growth resumed within 2 mo following treatment with P and within 1 yr following treatment with K. A leaf scorch symptom was associated with high Cl^- levels in leaves (1.9%). Normal leaves, free of scorch symptoms had 0.4- 0.8% Cl^- during midsummer. Boron (B) toxicity was characterized by marginal necrosis of mature leaves near the end of the growing season and was nearly universally present in the San Joaquin Valley of California. Necrosis-free leaf tissue, without and with marginal necrosis, had 220- 235 ppm B while necrotic marginal tissue had about 1,000 ppm B.