Use of Potassium Silicate Amendments in Recirculating Nutrient Solutions to Suppress Pythium ultimum on Long English Cucumber. M. Chérif, Graduate Research Assistant, Département de phytologie, Faculté des Sciences de l’Agriculture et de l’Alimentation, Université Laval, Québec, Canada G1K 7P4. R. R. Bélanger, Assistant Professor, Département de phytologie, Faculté des Sciences de l’Agriculture et de l’Alimentation, Université Laval, Québec, Canada G1K 7P4. Plant Dis. 76:1008-1011. Accepted for publication 4 May 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1008.

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. No significant differences were observed between the 100- and 200-ppm silicate treatments. Results were better when greenhouse conditions favored spread of P. ultimum. Silicon alone did not increase cucumber yield, suggesting that it acts as a disease suppression agent rather than as a fertilizer. The phenomena by which silicon confers protection against P. ultimum infection and disease development are not fully understood, but our results indicate that mechanisms other than a mechanical barrier to fungal penetration are involved.