Spots first appear as small, elongated, water-soaked marks in the form of irregular, angular lesions between the veins. As they age, they become brown to black and develop a yellow margin. The most effective method for control of this disease is selection of a site with well-drained soil. It is also very important to discard any corms that show disease symptoms. Symptoms appear as a light and dark green mottling or a mosaic pattern on the leaves.
Control involves roguing and removing infected plants as soon as they are detected.
Rusty spots of dead tissue develop on leaves, usually after periods of rain followed by bright sunshine. This disease is not serious and can be minimized by watering early in the day or by avoiding overhead irrigation. Insect Problems Cutworms. Various species of cutworms occasionally injure gladiolus. Perhaps 14 or 15 species of moths, the larvae of which are called cutworms, can be damaging.