Field trials of citrus black spot control in Taiwan
Tsia, Y.P.; Shiao; Liau, T.H.; Sun, M.H.
Plant Protection Bulletin, Taiwan 19(2): 140-145
A total of ten field trials were conducted at seven locations throughout Taiwan in 1976 for evaluating the effectiveness of fungicides and fungicide-oil mixtures against the black spot disease (Guignardia citricarpa Kelly) in ponkan (Citrus poonensis Hort.), tankan (Citrus tankan Hay.) and liu-cheng or sweet orange (Citrus sinensis Obs.). Field plots were designed to include seven treatments with four replications and five trees in each replication. Fungicides were applied eight times at approximately 2-week intervals following the flowering stage; whereas fungicide-oil mixtures were applied four times at approximately 4-week intervals. The status of all experiments is given in Table 1. At harvest, 40 fruits were randomly sampled from each tree for calculation of black spot index and percentage of spot-free fruit. In all the three kinds of citrus tested, four applications of Benlate-oil mixture, two applications of Dithana M-45-oil mixture followed by two applications of Benlate-oil mixture, both at 4-week intervals, and eight applications of Benlate at 2-week intervals gave the same and the best results of black spot control as well as the production of black spot-free fruits. Moreover, no visible phytotoxicity was observed on citrt. trees treated with either fungicde-oil mixtures or oil alone. The addition of the mineral oil orchex 796 to fungicides reduced not only the concentration of fungicides to two-thirds but the application frepuency to one-half.