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. Stromatinia gladioli Do not plant infected corms. Purchase corms that have been treated with hot water and fungicides. Plant in soil that has been pasteurized with chemical fumigants or steam. If infection is noted after planting, apply PCNB or vinclozolin until flower production is complete.