Collar and root rot of aibika (Abelmoschus manihot) I. Pathogenicity and effect of systemic fungicides

Abstract

Collar and root rot disease of aibika (Abelmoschus manihot (Linnaeus) Medicus) is caused by the fungus Phytophthora nicotianae var. nicotianae B. de Hann. A pathogenicity study conducted in the glasshouse showed that the fungus infects the collar region of the stem and then progresses downwards to destroy the root system, killing the plant. Field and glasshouse trials using three systemic fungicides, Ridomil 5G (metalaxyl), Le-San DX 70 WP (fenaminosulf) and Plantvax 5G (oxycarboxin) were carried out to study their effect on the disease. Aibika plants were inoculated with the fungus. In the field trial fungicides were applied at 5g product per plant after the plants became infected. Ridomil and Le-San DX gave significant control of the disease and increased yields. In the glasshouse trial the fungicides were applied at 2, 5 and 10 g product per plant. Ridomil and Le-San DX were effective at 5 g. At 10 g both fungicides were phytotoxic. These two fungicides had a curative effect on the disease. Time of application of fungicides appeared to be critical in obtaining control of the disease.