SENSITIVITY OF SOME PATHOGEN ISOLATES TO FUNGICIDES COMMONLY USED IN VEGETABLE GREENHOUSES IN ZIMBABWE

Abstract

The adoption of greenhouse technology for the production of high value vegetables is on the increase in Zimbabwe. This production system is chemical intensive in pest, disease and mineral nutrition management. This study sought to survey the prevalence of fungal diseases in greenhouse grown tomatoes, cucumber and green pepper in and around Bulawayo and to investigate the sensitivity of the isolated fungal pathogens to commonly used fungicides. Infected plant parts were collected for laboratory analyses from clearly diseased plants. Six fungal pathogens, namely Phytophthora infestans, Fusarium oxysporum f. Sp lycopersici, Peronospora, Botrytis cinerea, Leveillula taurica and Spaerotheca fuliginea, were isolated from these crops in the laboratory. These fungal isolates were evaluated for their susceptibility to the following commonly used fungicides: Copper Oxychloride, Chlorothalonil, Dithane M-45, Saaf and Didecyl Dimethyl Ammonium Chloride (DDAC – Spore Kill), using the broth macro-dilution method. The fungal isolates showed varied sensitivity to the test fungicides. All fungal isolates were completely inhibited by all the concentrations of Copper Oxychloride and Chlorothaloni used, except for Phytophthora infestans, which showed resistance at all the concentrations of these fungicides used, and Fusarium oxysporium which was resistant to 0.075 % Chlorothalonil. Both Dithane and Saaf were able to inhibit fungal growth at the recommended concentration, i.e. 0.2 %. Spore Kill (DDAC) completely inhibited all the fungal isolates at all the concentrations used. The best fungicidal activity was obtained with Spore kill, followed by Copper Oxychloride and then Chlorothalonil. Phytophthora infestans displayed resistance to all the fungicides except to Spore Kill, followed by Fusarium oxysporium. Botrytis cinerea was the most susceptible isolate to all the fungicides tested. All fungicides were effective at, or just below, their recommended concentration levels, except for Spore Kill which was effective across the board. Even though Spore Kill is a recent addition to the fungicides currently in use in greenhouses in Zimbabwe, the results of this study show that it can be adopted as a preventative fungicide in greenhouses with high levels of success.