Proc. of Second World Avocado Congress 1992 p. 497

Preharvest Biological Control of Avocado Postharvest Diseases

Lise Korsten and Jan M. Kotze

Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria 0002, Republic of South Africa

Abstract. In South Africa biological control is a new approach to avocado postharvest disease control. In this report, the biological approach is evaluated against pre-harvest applications of copper oxychloride. Antagonists Bacillus lichineformis and B. subtilis effectively reduced stem-end rot, anthracnose, and the Dothiorella/Colletrotrichum fruit rot complex when applied as preharvest sprays. Integrated control using copper oxychloride followed by a B. subtilis spray later in the season was also effective in reducing postharvest disorders. A B. subtilis spray applied four times at 10⁸ cells/ml was the most effective treatment in controlling all three postharvest diseases and could even give sustained protection throughout the harvesting season. Reevaluating the same treatments the following year, without repeating the biological and integrated spray programs, the four-time B. subtilis treatment gave control comparable to the copper oxychloride treatment, which was repeated.