Cause Fusarium oxysporum f. sp. tulipae, a fungus that lives in soil and on plant debris. The disease became a problem with shorter rotations that favored buildup of inoculum. The disease is widespread but not as common or severe as Fire (Botrytis blight); it is worse on some tulip cultivars and occurs primarily in storage. Symptoms may be more severe at higher (61°F) than lower (54°F) temperatures. These fungi penetrate through the roots into the tissue of the planted bulbs and colonize the basal plate of the young bulb in the field. Infection more frequently occurs on the fleshy outer scale of the new bulb.
Symptoms Leaves turn red, and plants wilt and often die. The bulb base and roots rot. Spots may also develop on the top or sides of the bulb. When diseased bulbs go into storage they become dull white with firm shrunken bases that usually are covered with whitish or pinkish fungal growth. If other organisms enter the decayed area, it may become soft and develop a rank smell. Symptoms usually are most evident in storage rather than in the field. When diseased bulbs are forced in the greenhouse for flowering, stunted growth and leaf yellowing occurs within a few weeks. Plants generally die before flowering. The basal plate and roots decay and become a dull gray. The decay spreads to the bulb scales and lower stem. Fine dark streaks may be seen in the stem.
Cultural control
- Avoid wounding the bulb.
- Sort out and destroy infected bulbs.
- Rotate out of bulbs for 3 to 4 years.
- Plant in heavy but well-drained soil.
- Avoid high rates of nitrogen using nitrate forms rather than ammonium forms.
Chemical control Postharvest soak of sorted bulbs then dry thoroughly and quickly before storage.
- 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 clean bulbs for 15 min. 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. Oregon only.
- 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 fl oz/100 gal water at 55°F to 75°F. Soak bulbs 15 to 30 min, then let dry. Group 1 fungicide.
- 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 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.
Reference Schenk, P.K. and Bergman, B.H.H. 1969. Uncommon disease symptoms caused by Fusarium oxysporum in tulips forced in the glasshouse after pre-cooling at 5°C. Netherlands Journal of Plant Pathology 75:100-104.