Cause Burkholderia gladioli pv. gladioli (formerly Pseudomonas gladioli pv. gladioli), a bacterium. Unlike other gladiolus corm rot diseases, scab does not kill the affected plants. Unless very severely affected, corms produce normal flower spikes. The bacteria are widespread and may be introduced into a planting on infected corms or may have survived from a previous planting. Insect feeding wounds, such as those from bulb mites, may serve as infection sites.
Symptoms Shallow black surface lesions develop on the corms. Typical scab lesions are sunken, have a definite rim, and have a hard, shiny black layer over the surface of the lesion. Lesions are more numerous at the base of the affected corm; in contrast, Stromatinia lesions are more numerous on the upper portion of affected corms, particularly in the leaf scar region.
Cultural control
- Plant only scab-free corms.
- If possible, do not plant in soil that has produced heavily scabbed corms.
- A 3-year rotation is recommended.
- Control bulb mites. See PNW Insect Management Handbook for details.
Reference Forsberg, J.L. 1965. The relationship of Pseudomonas marginata, Stromatinia gladioli, bulb mites, and chemical soil treatments to the occurrence and control of scab and stromatinia rot of gladiolus. Phytopathology 55:1058.