Overview

The three-year crop rotation experiment intended to suppress/manage pink root disease and root-knot nematode populations in onion-growing areas showed a dramatic reduction in pink root incidence after pepper, rice, and cucumber were planted as rotation crops for two consecutive years, from 70-90% incidence to less than 15%. The disease severity was highest for the onion-fallow-rice-onion scheme, followed by the onion-pepper-rice-onion scheme, then by the mungbean-pepper-fallow-onion scheme, in decreasing order. Onion yields did not differ significantly among the treatments. So far, the mungbean-pepper-fallow-onion rotation pattern appeared to be the most effective for pink root suppression.

Initial populations of Meloidogyne graminicola were too low to provide conclusive results. The effects of the varying cropping schemes on nematode populations, therefore, were not clear, being aggravated during the last cropping season by the unusually hot and dry weather conditions caused by the El Nino phenomenon.