| dc.description |
Three fungicide rates, 4·48, 2.24, and 1.12 kg peT ha, and four spray intervals, 5<sup>−</sup>, 7<sup>−</sup>, 10<sup>−</sup>, and 14-day intervals, were investigated for the control of Phytophthora leaf blight of taro in a subtropical field environment in Hawaii. The fungicide rate was studied in two separate locations on the windward sides of the island of Kauai. The fungicide utilized in these experiments was a co-ordination product of zinc ion and manganese ethylene bisdithiocarbamate (Dithane M-45, 80 per cent WP). In the lower rainfall location, there was no difference due to different fungicide rates while in the wetter location, the 4·48 kg per ha rate gave better control than the 1·12 kg per ha rate. There was no significant difference between the 5<sup>−</sup>, 7<sup>−</sup>, and IO-day spray intervals but when compared with the 14-day interval, the 5-day interval was superior. Periods of increased rainfall were reflected in the following week by increased lesion counts. Present data indicate that rainfall is a major factor to consider as a basis for predicting disease was occurrences and may be utilized for planning interval of fungicide application. The amount of disease was a function of initial disease levels, rainfall, temperature, relative humidity, fungicide rate, and spray interval between fungicide applications. Applications of fungicide at weekly intervals when weekly rainfall accumulation exceeded 1 cm per week and/or when lesion counts exceeded more than one per plant gave substantial disease control. Thus, once these parameters of disease have been established, fungicide application could be governed conveniently by monitoring rainfall and disease incidence to achieve practical Phytophthowra leaf blight control. The 2·24 and 4·48 kg ha<sup>-1</sup> rates gave significant yield increases over the 1·12 and check (no fungicide) treatments where Phytophthora leaf blight occurred in epidemic proportions. |
