Development of a systems approach for the control of diseases in organic greenhouse crops
The study aimed to develop integrated crop management (ICM) systems in organic greenhouse production for improved control of tomato corky root rot (Pyrenochaeta lycopersici), tomato verticillium wilt (Verticillium albo-atrum), and cucumber powdery mildew (Podosphaera xanthii), compatible with and/or utilizing organic fertility management practices, while minimizing or eliminating permitted practices such as soil disinfection by steaming and foliar application of sulphur fungicide. Different concentrations of chitin (or chitosan -a water soluble form), fresh Brassica tissues, and cow manure based compost applied to soils infected with P. lycopersici alone and P. lycopersici plus V. albo-atrum reduced disease incidence and/or increased yield. However, efficacy differed between treatment types and concentrations. Compost or fresh Brassica tissue significantly increased soil microbial activity which may have increased competition and/or antagonism against soil pathogens, lowering disease incidence. Combining different treatments gave no synergistic or additive effects on incidence of both diseases, but the Brassica tissues plus chitosan combination improved yield. In tests of cultivar resistance/tolerance to the two pathogens, two "standard" cultivars were susceptible to both pathogens whilst the cherry type was tolerant to corky root rot, but not Verticillium. In soils infected with corky root rot only, grafting the cultivars onto a resistant root-stock effectively reduced disease incidence, but when infected with both pathogens, only one "standard" cultivar showed reduced disease incidence. In cucumbers, foliar application of chitosan reduced powdery mildew but Milsana® VP 2002 (a plant extract) was significantly better. Ampelomyces quisqualis and Pythium oligandrum (Biological Control Agents) were ineffective. There was no synergistic or additive effect detected with any combinations. Resistance/tolerance of cultivars significantly affected disease incidence. However, the more susceptible cultivar outyielded the tolerant one despite greater infection. Several components of an integrated strategy for control of diseases were identified with significant potential for development of more sustainable, organic protectedcropping systems.