Elad, Y., Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel
Kirshner, B., Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel

Biological control of grey mould caused by Botrytis cinerea is achieved by Trichoderma harzianum under commercial greenhouse conditions. The establishment of populations of Trichoderma in the phylloplane of treated plants was studied. After several applications of a formulated preparation, a level of 105 cfu per leaf was established. High relative humidity (r.h.) but not saturation favoured establishment and biocontrol activity of T. harzianum. T. harzianum affected the level of natural bacterial and fungal populations, resulting in an increase or decrease in comparison with nontreated leaves. However, r.h., temperature, plant nutrition, plant species, and leaf age influence the effect of the biocontrol agent on the indigenous microflora. It is suggested that microclimatic conditions affect Trichoderma establishment more than does plant nutrition. © 1992 Springer Science + Business Media B.V.