Cause Fusarium oxysporum f. sp. gladioli, a soilborne fungus that survives in soil and plant debris for many years as chlamydospores. It can survive in the absence of gladiolus for many years. Population levels are highest in the top 8-inches of soil and the disease is favored by high soil temperatures. Spores infect roots then mycelia travels up the roots and crosses the basal plate. The fungus in 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 stains of the fungus as isolates from gladiolus may infect iris but isolates from iris may or may not infect gladiolus.
Symptoms Reduced plant growth, stunting and yellow leaves are observed above ground. Yellowing increases until the plant dies. The roots are killed and become dark brown or decay, dropping off when corms are lifted. Infected corms may have dark brown, circular, rotting areas on the side or top; a shallow, dark brown basal rot; or only a light discoloration of conducting tissues above the basal plate. A dry corm rot may develop in storage if corms have not matured properly or are not cured soon after digging.
Cultural control Sanitation is important to focus on while integrating many other tactics.
- Select clean planting stock and discard all diseased corms. Corms grown from cormels in clean soil usually are healthier than corms grown from corms.
- Plant in clean, well-drained soil.
- Use a 4-year rotation.
- Avoid excessive nitrogen fertility.
- Cure corms quickly after digging. Best results are from curing 48 hr at 95°F, turning corms once after 24 hr and circulating the air at 200 cu ft/min. Results were good at lower temperatures, but more time was required. Hold corms for 5 days at 80°F and for 2 weeks at 70°F to cure corms to the same extent.
- Store at temperatures of 50°F or less, discarding all diseased corms before storing.
- It has been suggested that keeping the soil pH between 6.6 and 7.0 and utilizing nitrate forms of nitrogen may be helpful.
Chemical control Remove disease bulbs and soak clean bulbs for 15 to 30 min within 48 hr after digging. Research in India suggests that fungicides may be more effective when used at a low pH (3.0); however, this has not been confirmed in the PNW.
- Chipco 26019 FLO at 2 quarts /100 gal water. Label limits soak to 5 min. Group 2 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. 12-hr reentry.
- Postiva at 10 to 28 fl oz/100 gal water as a drench. Group 3 + 7 fungicide. 12-hr reentry.
- Terraguard SC at 4 to 8 fl oz/100 gal water as a drench. Group 3 fungicide. 12-hr reentry.
- Thiophanate-methyl-based products can be used as soaks. Group 1 fungicides. 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.
Biological control Use in conjunction with other control tactics such as thorough sanitation.
- Asperello T34 (Trichoderma asperellum strain T34) at 0.35 oz/35 sq ft of substrate before potting. See label for details. 12-hr reentry. O
- RootShield Plus Granules (Trichoderma harzianum Rifai strain T-22 and T. virens strain G-41) at 1 to 3 lb/cubic yard soil mix. No restrictions on reentry required when soil incorporated. O
- Bio-Tam 2.0 or Tenet WP or Obtego (Trichoderma asperellum and T. gamsii) at 0.5 to 1.5 lb/cubic yard of substrate. See label for details. No restrictions on reentry when soil incorporated. O
References Brayford, D. 1996. Fusarium oxysporum f. sp. gladioli. IMI Descriptions of Fungi and Bacteria No. 1266.
Ram, R., Manuja, S., Dhyani, D., and Mukherjee, D. 2004. Evaluations of fortified fungicide solutions in managing corm rot disease of gladiolus caused by Fusarium oxysporum. Crop Protection 23:783-788.