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ABSTRACT
Downy mildew of cucumber caused by the fungus Pseudoperonospora cubensis is potentially the most damaging disease of cucumbers in Poland since 1985, both in open field and under protected conditions. During 1996–1999, the potential for an integrated programme for control of cucumber downy mildew was examined. In order to obtain good control of disease, early detection of airborne Pseudoperonospora cubensis sporangia is crucial. This allows the first cycle of the fungus to be detected so that a preventive or curative fungicide can be applied at the optimum time. Investigations reported here identified the most effective products and mixtures for control of the disease in Poland as the tank mixture of Curzate M 72,5 WP (cymoxanil/mancozeb) with Bravo Plus 500 SC (chlorothalonil/zinc), Amistar 250 SC (azoxystrobin) and Tattoo C 750 SC (propamocarb/chlorothalonil). It is possible to predict the disease on cucumbers through the use of a forecasting system (the Metos®-DX Vegetable station) to enable the user to determine the periods of risk of disease and also the date of sporulation of the fungus.
This forecasting system was very effective, allowing the possibility of an early warning, particularly in terms of identifying the time of the first arrival of downy mildew inoculum, which signals commencement of chemical control. Studies were conducted on canning cucumber cultivars either susceptible (Śremski) or tolerant (Aladyn) to downy mildew. Both the contact and systemic fungicides (chlorothalonil/zinc and azoxystrobin, respectively) applied at full and half of their recommended rates gave a significantly higher level of disease control on tolerant cultivar (Aladyn) as compared to the susceptible cultivar (Sremski).
There was also the possibility to reduce the number of fungicide applications (by 3–4 on average) on the tolerant cultivar as compared to the susceptible one.