What Are the Brown Spots on the Gladiolus?

Fungal Bulb Disease

• Brown spots on gladiolus leaves may be an indication of fungal disease. The Septoria gladioli fungus, commonly known as septoria leaf spot, surfaces as small, round purple-brown or brown leaf markings. As the disease progresses, the outer portions of the spots darken. Black, spore-producing bodies show up against the spots' light-brown centers. This fungus also attacks the corm of the gladiolus, causing black, decayed areas that nearly consume the bulb. Septoria leaf spot is especially hard on closely spaced, newly emerging plants.

Bacterial Bulb Disease

• Planting gladiolus corms in poorly drained, wet soils invites neck rot from Pseudomonas marginata bacteria. Neck rot causes pinprick-sized, brownish-red spots on gladioli foliage. The spots typically surface at the bases of the leaves. Under wet conditions, they spread into soft, slimy patches. The shiny oozing leaves and stem collapse to the ground as neck rot progresses. The corms also ooze from concave, round spots. Their papery husks show dark lesions.

Leaf and Flower Diseases

• Two leaf-spot fungi can damage the stems and flowers of the gladiolus. Curvularia forms brown, oval spots on all three. As the infection progresses, the brown areas die. Darker brown rings separate the discolorations from surrounding yellow tissue. Botrytis, like Curvularia, destroys the ornamental value of the gladiolus. Its above-ground symptoms include brown leaf and flower lesions. As it progresses, the infection moves down the flowers from their petal edges to their centers, leaving them drooping, mushy and brown. In rainy conditions, the blooms develop a covering of gray spores. Botrytis also infects gladiolus corms, producing surface lesions and inner decay. Small, hard black growths on the corms or the dead leaves and stems are sclerotia. These structures allow the fungus to remain active in the soil for years.

Fungal Disease Management

• Gladiolus fungus control begins with dipping lesion-free corms in a solution of thiabendazole plus or iprodione fungicide and 80- to 90-degree Fahrenheit water. Mix the solution according to the manufacturer's specifications. Allow the corms to dry before planting them in well-drained, fertile sandy loam and full sun. Spray the sprouted plants weekly with captan or chlorothalonil fungicide in damp or wet weather if you see signs of Botrytis or Curvularia.

Bacterial Disease Management

• Scab bacteria usually infect gladiolus corms in wet soils or those infested with bulb mites, grubs or other bulb-chewing pests. Disease control includes applying insecticide to the the soil around the corms before refilling their planting holes. Water and feed the glads only as necessary. Dispose of diseased plants at the first sign of infection.