Cause Stromatinia gladioli, a soilborne fungus that survives in soil indefinitely (> 10 years). Sclerotia germinate in response to nearby gladiolus roots. Other hosts include crocosmia, crocus, and freesia. daffodil, iris, hyacinth and tulip are not hosts. The fungus enters leaves at or near the ground line and causes a dry rot of leaves and stem, which may kill the plant. Wounds are not required for infection. The disease is favored by cool, wet conditions, and wet soils. Often, secondary organisms enter the infected stem at ground level, causing a wet or slimy appearance. The neck-rot phase of the disease occurs primarily in early summer. Young corms tend to be more susceptible than older ones.
Symptoms Symptoms are similar to those of Fusarium yellows. Older leaves become partially yellow and dry; eventually all the leaves become dry and dead. The part of the leaf in soil shows a dry rot, and tiny black fungal sclerotia develop on the dead areas.
Corm infections result in a dry rot and usually do not completely break down corms as with Botrytis and Fusarium rots. Instead, dark surface lesions develop, most abundantly along old leaf scars. Infected areas usually do not extend far into the corm's flesh. Black sclerotia may also be observed in rotted cortical tissue of the roots.
Cultural control
- Select pathogen-free corms.
- If possible, plant in soil not previously planted to gladiolus.
- Plant in clean, well-drained soil.
- Use a long 4-year rotation.
- Remove volunteer plants that occur in areas previously planted to gladiolus.
Chemical control Effective (highly toxic) chemicals used in the past are no longer available for use.
Reference Jeves, T.M. and Coley-Smith, J.R. 1980. Germination of sclerotia of Stromatinia gladioli. Transactions of the British Mycological Society. 74:13-18.