Branch Dieback of Macadamias in South Africa Induced by Botryosphaeria ribis. J. A. Herbert, Citrus and Subtropical Fruit Research Institute, Nelspruit, South Africa. N. M. Grech, Citrus and Subtropical Fruit Research Institute, Nelspruit, South Africa. Plant Dis. 69:83. Accepted for publication 27 September 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-83D.
Following two dry years in South Africa, a severe branch dieback of macadamias (Macadamia integrifolia, M. tetraphylla Maiden & Betche) was seen in all major production areas. Botryosphaeria ribis Grossenb. & Duggar was consistently isolated from infected samples. Infected branches showed a typical brown-purple discoloration in the wood. Five 18-mo-old seedlings were inoculated with a fungal plug taken from an actively growing culture on potato-dextrose agar. Two of the five inoculated plants began to wilt after 4 wk and were dead after 5 wk; these plants showed the typical purple discoloration, and the pathogen was reisolated from them. Additional glasshouse trials and field surveys indicated water stress increased susceptibility of trees. Differences in susceptibility among varieties were also observed. The fungus is sensitive to benomyl; for interim control, pruning out infected wood below the infection, sealing the wound, and spraying the cut area with benomyl are recommended.