Timing fungicide applications for control of Scleroderris canker: efficacy of fungicides applied to spores, hyphae and diseased seedlings

摘要

The effects of the fungicides chlorothalonil (Bravo~R) and propiconazole (Tilt~R) on Gremmeniella abietina conidia, germinating conidia and growing mycelia were studied in vitro using liquid V8 medium and in inoculation experiments with Scots pine seedlings. In the first experiment the fungicides were applied to 0, 4, 8 and 12 day-old cultures and the dry weight of fungus mycelium was determined 16 days from the beginning of the experiment. Both fungicides prevented growth of conidia (0 days), andgerminating conidia (4 days). Growth of young, 8-day, hyphae was prevented by chlorothalonil, but not by propiconazole while neither fungicide prevented G. abietina growth when applied to 12-day-old cultures. Control of G. abietina on inoculated, 1-year-old Scots pine seedlings varied with the duration between inoculation and fungicide application over the three years (1994-95, 1996-97 and 1998-99) when the experiments were made. The percentage of diseased seedlings was higher in inoculations made in late August than in July. In general, best disease control occurred when the fungicides were applied within 10 days of fungus inoculation. Propiconazole, which effect was tested in 1996-1997, was much less effective than chlorothalonil in controlling G. abietina. Based on our results we fell that it is possible to prevent G. abietina infection in nurseries by applying fungicides during the time of spore liberation and dispersal.