Management of Plant Diseases without Using Pesticides in Sustainable Agriculture

Abstract

In solving growers new plant disease problems during the past three decades, various control methods without using any pesticide have been discovered. Through the systematic exclusion of each possible causal factor, and the confirmation of the working hypothesis by experimentation, several kinds of disorders were found to be due to nutrient deficiency and were controlled by application of appropriate nutrients. These include boron deficiency as the cause of latex secretion and deformity of papaya fruit, deficiency in calcium and boron as the cause of heart rot of banana tissue culture plantlets, and deficiency in nitrogen and phosphorous as the cause of ohia forest decline. The same approach was applied to discover hydrogen fluoride emitted from brick factories as the cause of marginal scorch of banana. The discovery forced the closing of several brick factories and the construction of new factories emitting insignificant amounts of hydrogen fluoride. Investigation of inhibition mechanism revealed that a soil suppressive to Pythium splendens was due to its high calcium content and high microbial population. Damping-off of cucumber was, therefore, controlled by mixing soil in planting holes with lime to increase calcium content and alfalfa meal to increase microbial population. Greenhouse tests confirmed the field observation that only young seedling roots are susceptible to Phytophthora palmiuora. The papaya replant problem caused by P palrniuora was subsequently solved by replanting seeds in small quantities of pathogen-free virgin soil placed in the planting holes. All banana cultivars are susceptible to fusarium wilt caused by Furariuni oxysporum f. sp. cubense. By screening tissue culture plantlets for resistance to the disease and selection for favorable traits from resistant clones, a resistant variety was released for commercial planting within 6 years. Among the extracts from various edible plants tested, sunflower oil was found to be very effective in controlling powdery mildews on several vegetable crops in the field.