Cause A fungus, Fusarium oxysporum f. sp. gladioli, that lives in soil and plant debris for many years as chlamydospores. Population levels are highest in the top 8 inches of soil. Spores infect roots and cross the basal plate. These infections may continue to enter and spread within the vascular tissues. The fungus is spread widely by contaminated soil and infected corms while local spread can be by water flow and rain splash. Excess nitrogen fertility may favor the disease. There may be several types or strains of the fungus because isolates from gladiolus may infect iris, but isolates from iris may or may not infect gladiolus.
Symptoms Lower leaves may be stunted or yellowed or may fail to emerge. Roots may be invaded and eventually rot as decay progresses into the bulb. The bulb's infected basal plate becomes shrunken, turning light brown or reddish brown. A fairly definite margin separates healthy and diseased tissue. The husk remains firmly attached in the rotted area and often is covered with a white or pinkish fungal growth.
Cultural control
- Avoid wounding.
- Destroy diseased bulbs.
- Rotate out of bulbs for 3 to 4 years.
- Plant in heavy but well-drained soil.
- Reduce planting density of infected stocks.
Chemical control Treat within 48 hours of digging.
- 42-S Thiram at 1.5 pints/8 gal water. Group M3 fungicide. 24-hr reentry.
- Daconil Ultrex at 2.5 to 5 lb/100 gal water. Soak bulbs for 15 min. before planting. Group M5 fungicide. 12-hr reentry.
- KleenGrow at 0.15 to 1.5 fl oz/gal water. Soak for 30 seconds and allow to drain.
- Medallion WDG at 8 oz/100 gal water. Soak sorted bulbs for 20 min then dry. Group 12 fungicide. 12-hr reentry.
- Mertect 340 F at 30 oz/100 gal water. Temperatures should be 55°F to 75°F. Soak bulbs 15 to 30 min, then let dry. Group 1 fungicide. 12-hr reentry.
- Thiophanate-methyl-based products as a postharvest soak at 80°F to 85°F. Soak clean bulbs 15 to 30 min. within 48 hours after digging. Group 1 fungicide. 12-hr reentry.
- Cleary's 3336 EG at 16 to 24 oz/100 gal water.
- OHP 6672 4.5 F at 16 to 20 fl oz/100 gal water.
Reference Brayford, D. 1996. Fusarium oxysporum f. sp. gladioli. IMI Descriptions of Fungi and Bacteria No. 1266.