Horticultural production systems have to move forwards to an environment-friendly and sustainable plant production. Basic substances can be added to reduce the use of synthetic plant protectant in conventional plant protection strategies. Regarding the protection of ornamental plants, less is known about the usage and behaviour of these alternative strategies and components. In our study, an infection of Podosphaera pannosa and Erysiphe polygoni in two different cultivars of cutting roses and one cultivar of French hydrangea was investigated. We studied the effect of a weekly foliar treatment of the basic substance chitosan (0.05 g/m2) compared to a water control and potassium hydrogen carbonate (VitiSan, Biofa GmbH, Münsing, Germany) in both production systems. As a result, in cutting roses as well as in French hydrangea, we found a significantly decreased infected leaf area following the use of chitosan and VitiSan compared to the water control. In both treatments, we found a stronger effect in French hydrangea, compared to roses. Results also indicate that the basic substance chitosan has to be used at a low pathogen level. We present a promising approach to reduce conventional plant protectants in ornamental plant production.

Alternative strategies in plant protection are required due to political and environmental conditions. Basic substances can potentially benefit for modern plant protection in conventional and organic horticulture. In the case of plant protection in ornamentals, little is known about the effect of basic substances within the canopy to reduce foliar diseases. Podosphaera pannosa is one of the most severe diseases in the production of cut roses. In this study, different cultivars of cut roses were sprayed weekly with an extract of Equisetum arvense (4 g dried plant material/L), an aqueous solution of hydrogen peroxide (10 g/L) and a commercial plant protection product containing potassium hydrogen carbonate (VitiSan, Biofa GmbH, Münsingen, Germany) during two experimental trials. As a result, the symptoms of infected leaf area could be reduced significantly as the experiments progressed. Furthermore, no negative effects such as a reduction of plant growth or the number of marketable flowers were observed. The results indicate that the foliar application of the basic substances hydrogen peroxide and E. arvense-extract has the potential to reduce the use of synthetic plant protection products in conventional and organic horticulture.