Evaluation of Copper-Based Fungicides for Downy Mildew Control on Cucumber in Commercial Greenhouses, Abuja FCT

Downy mildew of cucumber (Cucumis sativus), caused by Pseudoperonospora cubensis, is a major disease constraint in commercial greenhouse production systems in Nigeria, where high humidity and limited air exchange accelerate epidemic development. Copper-based fungicides remain widely available and affordable management options, yet their efficacy relative to newer systemic alternatives under Nigerian greenhouse conditions has not been comprehensively evaluated. This study compared the effectiveness of five copper-based fungicide formulations against P. cubensis on cucumber in 12 commercial greenhouse facilities across the Abuja Federal Capital Territory and adjacent Nasarawa State. Fungicide efficacy was assessed through biweekly disease rating of foliage using percent leaf area infected scales over two consecutive cropping cycles. Marketable cucumber yield and crop quality were recorded at each harvest cycle. Results showed that copper hydroxide applied at seven-day intervals provided the most consistent downy mildew suppression among tested copper products, reducing disease area under the progress curve by 68 percent relative to the untreated control and yielding 19.8 tonnes per hectare marketable fruit across both cycles. Copper octanoate and Bordeaux mixture showed inferior efficacy under the high-humidity conditions typical of poorly ventilated greenhouse structures. Phytotoxicity symptoms were observed in two facilities with inadequate irrigation management, resulting in a yield penalty in affected plants. The study recommends copper hydroxide as the preferred copper fungicide option in Nigerian greenhouse cucumber production and emphasises the importance of simultaneous ventilation improvement. Keywords: cucumber, downy mildew, copper fungicide, greenhouse, Abuja.