Disinfest cutting knives frequently. Maintain good mite and insect control. Water in a manner that keeps leaf surfaces dry. Avoid working on wet plants. Stemphylium Leaf Spot Small, round yellow spots have a distinct reddish center when held up to the light.
Mature leaves have the most spotting.
Stemphylium botryosum Apply mancozeb, ziram, or chlorothalonil before any disease begins. Stromatinia Dry Rot Corm scales are brown and may appear shredded. Small reddish-brown spots on the surface of the corm can be removed, leaving a clean, shallow, sunken area. Corms are dry, hard, and mummified. Clusters of plants are killed by neck rot.