Efficacy of cultural methods in the control of Rhizoctonia solani strains causing tomato damping off in Kenya

Abstract

Rhizoctonia damping off of tomato caused by Rhizoctonia solani can be a serious problem in most intensive production environments. Recent increase in smallholder vegetable production of 0.5-3.0 ha in Kenya has resulted in build up of the pathogen to above economic threshold levels. There is no effective chemical control or resistant varieties. Use of soil fumigants such as methyl bromide in the control of Rhizoctonia and other soil borne pathogens is not sustainable due to their high costs, and toxicity to man and environment. Cultural methods such as soil amendments, mode of planting and influencing soil moisture levels either alone or in combination with other methods are among the most likely substitutes to use of toxic fumigants for control of soil borne pathogens in agriculture. This study was undertaken to evaluate the effects of cow manure application, transplanting, planting on raised beds and varying watering interval on Rhizoctonia damping off of tomato as measured by percent seedling survival at 5-30 days after planting (DAP), disease severity at 30 DAP, percent crop stand at 60 DAP and fruit yield at maturity. The study was conducted in a field artificially inoculated with pathogenic strains of Rhizoctonia solani isolated from infected tomato plants and Rhizosphere soil sampled from the major production regions of Kenya. The efficacy of the various cultural strategies both singly and in combination on the Rhizoctonia damping off management was compared with the conventional disease control involving chemical fumigation with metham sodium and two chemical seed dressers (pencycuron, thiram, imidacloprid) and (captafol) as the standard. Cow manure application and shorter watering interval when used singly or in combination with other cultural methods produced lower disease control and yield. Transplanting, planting on raised beds and medium irrigation interval when used singly or in combination with other cultural strategies produced good disease control resulting in higher yield that compared favorably with the conventional disease control involving soil fumigation and seed dressing. The various cultural disease control methods documented in this study can be used alone and in integration with other compatible Rhizoctonia damping off of tomato control strategies. Furthermore the promising non-chemical strategies may form part of the urgently sought for alternative to use of hazardous fumigants in agriculture and since they are not specific, there is low risk of resistant development over time.

Key words: Cultural disease control, Rhizoctonia solani, tomato