Reduction in Pesticide Use in Plant Disease Control by Integration of Chemical and Non-Chemical Factors

Abstract

The long term goal of this research project was to improve control efficiency of Alternaria diseases while reducing fungicide use, by integration of chemical and non-chemical factors. Non-chemical factors were genotype resistance, age-related resistance and fertilizers. The Specific objectives were: 1) To quantify changes in resistance among genotypes and over time in terms of disease development and specific phases of the disease cycle; 2) To quantify the effects of fertilizers applied to the foliage alone, or in combination with a fungicide, on disease development; 3) To quantify the relative contribution of genotype resistance, age-related resistance and fungicide type to the reduction of disease development; 4) To develop a strategy for integration of chemical and non-chemical factors which will achieve optimal disease suppression. The influence of physiological age of cotton plants and of the individual leaves, on disease incidence and on the rate of lesion expansion of A. macrospora was examined on leaves sampled from the field. Both parameters increased with the physiological age of individual leaves but were not affected by the age of the whole plant. The hypothesis that enrichment of the foliage with nitrogen and potassium may enhance host resistance to Alternaria and thus reduce disease severity, was examined for potato and tomato (A. solani ) and for cotton (A. macrospora ). Under controlled environment conditions, application of urea or KNO3 resulted in some reduction in disease development; however, foliar application of both nutrients (8-10 sprays in total) did not affect Alternaria severity in the field. Systemic fungicides against Alternaria (e.g. , tebuconazole and difenoconazole) are more effective than the commonly used protectant fungicides (e.g. mancozeb and chlorothalonil). Concepts for the integration of genotype resistance, age-related resistances and fungicide for the suppression of Alternaria diseases were developed and evaluated. It was found that reduction in host resistance, with age and among genotypes, can be compensated for by adjusting the intensity of fungicide applications, i.e. by increasing the frequency of sprays and by spraying systemic fungicides towards the end of the season. In, moderately resistant cultivars protection can be achieved by spraying at longer intervals than susceptible cultivars. The concepts for integration were evaluated in field trials for cotton, potatoes and tomatoes. By following these concepts it was possible to save up to five sprays out of 8-10 in a growing season.