Cause Sclerotium delphinii, a fungus that can survive many years in soil as sclerotia. Infection usually occurs on the stems near the soil surface. A low percentage of sclerotia survived after only a month in the soil when dried first. The disease is widespread but not as common or severe as Fire (Botrytis blight), yet it can cause serious damage, especially in moist, warm soils. In the Pacific Northwest, crown rot is more common on bulbous iris, tulips and lilies than daffodils.
Symptoms Leaves turn red, and plants wilt and die. The lower stem and the bulb rot and generally are covered with the white thread-like fungal mycelium. Round, reddish brown sclerotia (fungal resting bodies) about 0.0625 to 0.25 inch in diameter often form on the lower stem and bulb.
Cultural control
- Remove and destroy infected plants and adjacent soil containing the fungal mycelium and sclerotia.
- Sort and clean bulbs carefully, destroying all infected bulbs, soil, and debris.
- Dig infected plants early if soil is warm and moist. Dry bulbs quickly and store in layers under dry conditions with good air circulation.
- Plant pathogen-free bulbs in noninfested soil.
- Wash equipment and machinery between fields.
Chemical control
- Moncut 70-DF at 1.63 to 6.53 lb/A as in in-furrow spray directed over the tops of planted bulbs prior to hilling. Do not use spray adjuvants. Washington only (SLN WA-040032B). Group 7 fungicide. 12-hr reentry.
- Terraclor 400 at 3 pints/3.2 gal water. Before planting, soak bulbs for 5 min. Add 1% sticker and maintain good agitation. Group 14 fungicide. 12-hr reentry.
- Preplant soil fumigation with metam-sodium.
Biological control
- RootShield Plus Granules (Trichoderma harzianum Rifai strain T-22 and T. virens strain G-41) at 2.6 to 6 lb/0.5 A in furrow. Active only in soil above 50°F. No restrictions on reentry required when soil incorporated.O
- Bio-Tam 2.0, Tenet WP, or Obtego (Trichoderma asperellum and T. gamsii) at 2.5 to 3 lb/A banded. See label for details and other application methods. Active only in soil above 50°F and may be more effective used 7 days prior to planting. No restrictions on reentry when soil incorporated. O
Reference Coley-Smith, J.R., Ghaffar, A. and Javed, Z.U.R. 1974. The effect of dry conditions on subsequent leakage and rotting of fungal scleroita. Soil Biology and Biochemistry 6:307-312.