|Leaves on mature plants have turned yellow and appear to have some type of mite or disease on them. Flowers are beautiful, but stalk and leaves are infected. Do you have any explanation why this has happened? Thank you|
|What you describe sounds like hollyhock rust. This rust, caused by the fungus, Puccinia malvacearum, is the most common disease of hollyhock. Under favorable environmental conditions, the disease spreads rapidly from leaf to leaf. Older leaves are usually killed, and plants become unsightly. The rust fungus overwinters in pustules on plant debris. In the spring, spores produced in the pustules are blown to young hollyhock plants where they initiate new infections.
Removing the first rusted leaves in spring as soon as symptoms are observed is an important part of control. Old plants should be cut down and burned or removed as soon as flowering is over. Care should be taken to clean up fallen plant debris. Fungicides containing chlorothalonil (e.g. Daconil 2787), mancozeb (e.g. Fore, Dithane, or Penncozeb), trifloxystrobin (e.g. Compass), or myclobutanil (e.g. Systhane) can be used for preventative control. Spraying should begin at the first sign of disease and continue at recommended intervals through early July. Follow label recommendations.
Best wishes with your hollyhocks!