Anthracnose (fungus – Colletotrichum malvarum): This is the most destructive disease on Hollyhock. Fungus attacks leaves, stems and petioles. Typical fungal leaf spots, black blotches on petioles and stems. May also infect lower portions of stems and roots. High temperature and humidity favor development of the disease. Remove and destroy infected plant material and use a regular fungicide application.
Rust (fungus – Puccinia lobata): This is the most prevalent disease on Hollyhock in Texas and all portions of the plant are subject to infection. Small brown spots appear on underside of leaves. On upper leaf surface spots are yellow-to-orange and larger. Spots may coalesce and kill large portions on the leaf. Removal and destruction of infected plant material and regular applications of a fungicide will control rust.
Leaf Spots (fungi – Cercospora spp., Alternaria spp., Septoria spp.): Small angular grayish spots are scattered irregularly over leaves. Dead tissue may fall out leaving a shot hole appearance. Removal and destruction of infected plant material and regular applications of a foliar fungicide.
Cotton Root Rot: (See section on Cotton Root Rot).