ARS | Publication request: Suppression of Zinnia Powdery Mildew in the Greenhouse with Silicon-containing Media Amendments

Submitted to: Journal of Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 10, 2010
Publication Date: June 15, 2010
Citation: Locke, J.C., Altland, J.E., Frantz, J. 2010. Suppression of Zinnia Powdery Mildew in the Greenhouse with Silicon-containing Media Amendments. Journal of Phytopathology. 100:S74.

Technical Abstract: We have previously reported that supplemental silicon supplied in hydroponic solution or soilless media can reduce the incidence and severity of powdery mildew (PM) on zinnia. This research reports the use of 1) silicon-containing organic amendments, 2) mineral compositions high in silicon content, and 3) drenched potassium silicate solution as delivery systems for silicon to zinnia grown in a peat-based growing medium. Efficacy varied with silicon concentration and/or availability in the amendments, amount of amendment supplied, and the disease pressure. Three of the amendments; rice (Oryza sativa) hulls (RH), chopped miscanthus grass (Miscanthus x giganteum) straw (MS), and chopped switchgrass (Panicum virgatum) straw (SG) reduced severity of PM ratings after three weeks but the degree of reduction decreased with increasing exposure time for all three. After 6 and 8 weeks, only RH and MS provided substantial reduction in disease. Declining protection correlates with a declining level of silicon in the zinnia leaf tissue and may correspond with a depleted silicon supply in the medium. Constant application of potassium silicate solution provided the best protection suggesting the need for a continuous supply of silicon to the leaf tissue and negating the potential of a slow-release supply of silicon from the amendments or an accumulated reserve of silicon in the zinnia tissue. Additional approaches are being explored to extend the usefulness of silicon supplementation in suppressing mildew.