INFLUENCE OF CAVITY SIZE, SEEDLING GROWING DENSITY AND FUNGICIDE APPLICATIONS ON KEITHIA BLIGHT OF WESTERN REDCEDAR SEEDLING GROWTH AND FIELD PERFORMANCE

To determine the influence of cavity size, seedling density and fungic ide application on severity of Keithia blight caused by the fungus Did ymascella thujina (Durand) Maire, western redcedar (Thuja plicata Donn ) seedlings were grown in styroblocks of 3 cavity sizes, thinned to 3 growing densities and sprayed several times monthly with mancozeb fung icide. After two growing seasons cavity size, seedling growing density and number of fungicide applications all significantly (P less than o r equal to 0.05) affected blight severity. Blight severity was inverse ly related to the number of mancozeb fungicide applications. The only significant two-way interaction was for cavity size and seedling growi ng density. Eighteen seedlings from each of the nine cavity sizes and seedling densities combinations were assessed for shoot height, root c ollar diameter and blight severity, prior to planting at both Holt Cre ek and Salmon Creek on Vancouver Island, British Columbia in March 199 4. Growth was reassessed during October 1994. Seedling height and root collar diameter increased significantly (p less than or equal to 0.05 ) with certain cavity size and seedling density combinations. Blight s everity increased significantly (p less than or equal to 0.05) for all nine treatments at both sites, however, between sites blight severity increased significantly (p less than or equal to 0.05) only at the we tter, Salmon Creek site.