Why is my hosta foliage turning brown?

Botrytis on hosta

A.  The cool, damp, cloudy spring we had this year is conducive to many fungal infections. Some of the more common fungal problems affecting hostas are anthracnose and botrytis. This season, Plant Information has seen many cases of hostas infected with botrytis, which can be prevalent in cool, wet weather. Botrytis on hosta first appears on foliage as water-soaked spots that begin small and increase in size. As the spots enlarge, cinnamon to dark tan rings can sometimes be seen within the lesions. Lesions can also travel down to the petiole of the plant. Anthracnose can affect hosta during warm, wet weather. Symptoms appear as large, irregularly shaped, tan to brown spots with dark borders. The centers of the spots can fall out, giving the plants a tattered appearance. 

Cultural practices can help control both of these fungal diseases. Supplemental water should be applied early in the day so leaves have plenty of time to dry and do not remain wet for an extended period of time, which can facilitate the spread of fungal spores. Water should also be applied to the soil at the base of the plants, and not to the foliage. Plants placed too close together should be thinned to allow for better air circulation. Infected plant leaves should be removed and destroyed to eliminate inoculum. Pruners used to remove leaves should be sanitized with rubbing alcohol or a ten percent bleach to water solution to keep from spreading the fungi to other plants. Fungicidal treatments may be applied to healthy foliage as a preventative. Please contact Plant Information Service at (847) 835-0972 or plantinfo@chicagobotanic.org for accurate diagnoses and appropriate fungicide recommendations.