Brassica Green Manure Amendments for Management of Rhizoctonia solani in Two Annual Ornamental Crops in the Field

Abstract

Brassica green manure soil amendments are a possible alternative to chemical management of soilborne diseases of ornamental landscape and bedding plants. The objective of this study was to determine the importance of crop selection and application rate of brassica green manures for disease caused by Rhizoctonia solani on impatiens and petunia. Microplot experiments were conducted over 2 years using brassica green manure soil amendments for R. solani management of both petunias and impatiens. Brassica crops used were Brassica juncea ‘Fumus’ and ‘Bionute’, and Brassica napus ‘Jetton’, at the application rates of 700, 1400, and 4200 g·m−2 fresh weight aboveground biomass. Microplots were artificially infested to evaluate disease on these ornamentals, with a second set of experiments using noninfested plots to examine effects of the green manure alone on plant growth. All brassica green manure crops reduced disease symptoms in both impatiens and petunias. Rate of brassica application was more important than brassica crop variety for use as a green manure. The highest rate of the brassica green manure decreased crown lesions by 21% and 24%, root discoloration by 9% and 7%, and R. solani isolation by 15% and 8% for impatiens and petunias, respectively, for 4200 g·m−2 compared with 700 g·m−2 rates of application. No phytotoxic effects were observed from the brassica green manures following a waiting period of 4 weeks between amending the soil and planting the ornamental crops.