Peronospora sparsa

Peronospora sparsa is a plant pathogen that causes downy mildew on rose and diseases on caneberries and stawberries. In climate controlled greenhouses it doesn't occur so often because of the lack of free water maintained by humidity settings in the climate computers. In greenhouses without heating and without humidity controls and with Free Water Spots (FWS's), the disease can wipe out Downy Mildew susceptible rose varieties in 3 to 4 days completely, if unchecked.