<h2 style="margin-top: 0px !important; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0.4em; padding-right: 12px; padding-bottom: 0.5em; padding-left: 38px; border-top-width: 1px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: #88bbee; border-image: initial; font-weight: normal; font-size: 1.6em; font-family: 'Trebuchet MS', sans-serif; vertical-align: baseline; display: inline-block; clear: both; line-height: 1.35em; border-top-style: solid; width: 564px; color: #003366; background-image: url('http://www.rhs.org.uk/App_Themes/RHSGlobal/images/hbluebg.gif'); position: relative; text-align: left; background-repeat: repeat no-repeat;">What is rose powdery mildew?<a style="border-style: initial; border-color: #88bbee; border-image: initial; font-size: 23px; font-family: inherit; vertical-align: baseline; text-decoration: none; color: #003366; border-width: 0px; padding: 0px; margin: 0px;" title="Back to top" href="http://apps.rhs.org.uk/advicesearch/profile.aspx?PID=748#top"><img id="ctl00_body1_ctl00_imgBtt" style="margin-top: 0px; margin-right: 8px; margin-bottom: 0px; margin-left: 0px; border-style: initial; border-color: initial; font-family: inherit; vertical-align: baseline; border-width: initial; float: left; clear: left; position: absolute; top: 8px; left: 12px; height: 20px; width: 20px; padding: 0px;" src="http://apps.rhs.org.uk/advicesearch/Images/blue_backtotop.gif" alt="Back to top" /></a></h2>
<span style="color: #000000; font-family: 'Lucida Sans Unicode', 'Lucida Grande', sans-serif; font-size: 14px; line-height: 21px; text-align: left;">Rose powdery mildew is a disease of roses caused by the fungus <em style="border-style: initial; border-color: initial; border-image: initial; font-size: 14px; font-family: 'Lucida Sans Unicode', 'Lucida Grande', sans-serif; vertical-align: baseline; color: #000000; line-height: 21px; text-align: left; border-width: 0px; padding: 0px; margin: 0px;">Podosphaera pannosa<span style="color: #000000; font-family: 'Lucida Sans Unicode', 'Lucida Grande', sans-serif; font-size: 14px; line-height: 21px; text-align: left;">. The conspicuous white growth can affect all aerial parts of the plant, producing microscopic spores that spread the disease. High humidity is favourable for infection, and plants growing in areas where air movement is poor or the soil is dry can be severely affected.