Control of powdery mildew (Erysiphe polygoni) in tomato by foliar applications of compost tea.

Abstract

The use of compost tea extracts to control leaf diseases is an alternative that enables the use of chemicals in agriculture to be reduced. However, little is known about the mechanisms responsible. We examined an aerated compost tea prepared from composted market and garden wastes and tested its effect on naturally occurring powdery mildew disease produced by the foliar pathogen Erysiphe polygoni in tomato plants (Lycopersicon esculentum cv. Roma) grown in perlite in an unheated greenhouse. Untreated plants showed whitish patches of powdery mildew, while in the treated plants the mycelium could hardly be seen and leaves only showed localized yellow spots corresponding to former sites of infection. Tea compost reduced disease incidence by 19% when used as a preventive treatment and eradicated the pathogen on the leaves when applied as a curative treatment. Treatment was not associated with increased peroxidase or chitinase activity in the leaves and induction of local resistance is unlikely to have been responsible. Instead, the effects of the compost could be due to the presence of bacteria and fungi, which may act as antagonists to the pathogen. The compost was rich in inorganic salts, organic carbon and phenols, which can affect pathogen growth and phyllosphere microorganisms.