Fusarium Rot (fungus – Fusarium oxysporum f. sp. gladioli): Corms decay with a brownish-to-black dry rot of the tissue. The foliage of affected plants first turn yellow and then brown. Roots are killed. When diseased corms are planted, many may rot before producing plants while other produce weak plants that soon die. Before planting, inspect and remove all corms that have discolored areas or lesions. Healthy appearing corm should be chemically treated before planting.
Scab (bacterium – Pseudomonas marginalis): Small definitely outlined lesions appear on diseased corms. The lesions are circular, water-soaked and pinpoint to one-fourth inch diameter. A gummy ooze is produced from these spots that is yellow-to-dark brown in color. The lesions are rather shallow. Badly affected plants may die while those less affected have an unthrifty appearance. Mites that occur in the soil seem to serve as a vector and should be controlled with soil treatment if this disease is a problem. Do not plant infected corms. Rotate areas where gladiolus are planted.
Botrytis Blight (fungus – Botrytis spp.): Leaves, stems, flowers and corms are infected. Leaf spots are variable in size and shape. Infected flowers decline rapidly and have grayish fungal growth on the surface. The tissues become moist and slimy. Under severe conditions the entire top may be killed. Infected corms have irregularly shaped sclerotia attached to them. Affected corms should be discarded. Use suggested fungicides for controlling the disease on above-ground plant parts.
Other Leaf Spots (Bacterium-Bacterial Leaf Blight – Xanthomonas spp.): Water-soaked spots appear on leaves with a bacterial ooze occurring during wet periods. (Fungus – Septoria Leaf Spot – Septoria gladioli) Small rot. (Fungus – Stemphyllium Leaf Blight – Stemphyllium spp.) Light green-to-yellow lesions form on leaves. Spots turn red.
Virus or Virus-Like Diseases (Virus-Mild Mosaic): Caused by the bean yellow mosaic virus. Produces angular light and dark green mottling of leaves and flower stems. Virus is transmitted by aphids. (Mycoplasma – Aster Yellow) Flower parts remain green and fail to form normal color pigment. Plants turn yellow and degenerate prematurely. (Virus – White Break Mosaic) Caused by the cucumber mottle virus. Causes flowers to be blotched, open slowly and fade early. Plants are stunted. (Virus – Ring Spot) Caused by the tobacco ring-spot virus. Ring spots appear on leaves but flower parts are not affected.