DLO Research Institute for Plant Protection (IPO-DLO), P.O. Box 9060, 6700 GW Wageningen, the Netherlands
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Accepted for publication 6 March 1998.
The effect of treatments with conidial suspensions of Ulocladium atrum and Gliocladium roseum on leaf rot of cyclamen caused by Botrytis cinerea was investigated under commercial greenhouse conditions. Spraying U. atrum (1 × 106 conidia per ml) or G. roseum (2 × 106 conidia per ml and 1 × 107 conidia per ml) at intervals of 2 to 3 weeks during the production period and spraying U. atrum (1 × 106 conidia per ml) at intervals of 4 to 6 weeks resulted in a significant reduction of natural infections of petioles by B. cinerea. U. atrum or G. roseum (1 × 107conidia per ml) was as effective as the standard fungicide program. B. cinerea colonized senesced leaves within the plant canopy and infected adjacent petioles and leaves later. The antagonists colonized senesced leaves and reduced B. cinerea development on these leaves. Thus, the inoculum potential on petioles adjacent to necrotic leaf tissues was reduced. The fate of U. atrum conidia on surfaces of green cyclamen leaves during a 70-day period after application was studied. The number of conidia per square centimeter of leaf surface remained relatively constant during the entire experiment. Sixty percent of the conidia sampled during the experiments retained the ability to germinate. When green leaves were removed from the plants to induce senescence and subsequently were incubated in a moist chamber, U. atrum colonized the dead leaves. Senesced leaves also were colonized by other naturally occurring fungi including B. cinerea. On leaves treated with U. atrum from all sampling dates, sporulation of B. cinerea was significantly less as compared with the untreated control. Our results indicate that early applications of U. atrum before canopy closure may be sufficient to achieve commercially satisfactory control of Botrytis leaf rot in cyclamen.
© 1998 The American Phytopathological Society