Fertilization must avoid an excess of nitrogen as it stimulates rapid vegetative growth of the plant, which favours disease development. Application of fertilizers rich in potassium and phosphorus, as well as application of agrochemicals at the maximum tillering to booting stages or after a typhoon or a severe flood are common practices (Goto, 1992; Ho and Lim, 1979; Mizukami and Wakimoto, 1969).