| Botrytis Blight | Brown spots that may have reddish margins develop on leaves. Spots can be very small to over 1/2 inch in diameter. Similar spots on stems become soft and rot in wet weather. Small, clear spots on petals become brown. A neck rot may occur at the soil line. Small black granules (sclerotia) form on the surface of the infected corms. | Botrytis gladiolorum | Do not plant infected corms. Purchase corms that were treated with hot water and fungicides. Apply a fungicide to protect plants. |
| Curvularia Leaf Spot | Long, rectangular spots on leaves are tan with a brown margin and yellow halo. Concentric rings form within the enlarging spots. Corms rot. | Curvularia trifolli f. sp. gladioli | Do not plant infected corms. Plant in pasteurized soil. Apply a fungicide to protect plants. |
| Fusarium Yellows | Roots have brown spots or general rot. Older leaves yellow. Flower size, shape and color may be abnormal. Flowers may not develop while stalks are curved in an S-shape. Corms rot from the center outward. Oval, sunken spots on the corm surface are brown and may have concentric rings. | Fusarium oxysporum f. sp. gladioli | Do not plant infected corms. Maintain a soil pH of 6.6-7.0 and use nitrate as the nitrogen source when fertilizing. |
| Nematodes | Root system is small. Plants are stunted and flower late. Galls may form at nodes. Fusarium yellows may be severe. | Meloidognye, Pratylenchus, Trichodorus, Belonolaimus, Ditylenchus, Hemicyliophora, Rotylenchus | Plant in soil that has been steamed or chemically pasteurized. Maintain good weed control. |
| Scab | Brown, round, sunken areas with raised edges are on corms. A soft rot of the neck develops. | Pseudomonas marginata | Do not plant infected corms. 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 a fungicide to protect plants. |
| 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. If infection is noted after planting, Apply a fungicide to protect plants. |
| Viruses | Flowers are small, distorted or have color breaking. Leaf tissue may be mottled, have white flecks, or reddish blotches. | Bean yellow mosaic, cucumber mosaic, tomato ringspot, tobacco ringspot. | Maintain good insect control. Plant in pasteurized soil free of nematodes and weeds. Destroy infected plants as soon as they are found. |
