Amendment of a recirculating nutrient solution with potassium silicate was evaluated as a means to control Pythium ultimum infections on long English cucumber (Cucumis sativus). Supplying the solutions with 100 or 200 ppm of silicate significantly reduced mortality, root decay, and yield losses attributed to infection by P. ultimum. Treating inoculated plants with potassium silicate increased root dry weights and number of fruit, especially high-grade fruit. Results were slightly superior to noninoculated controls. The two cultivars tested, Corona and Marillo, responded similarly to the treatments (.)