Cause Sclerotinia sclerotiorum is a fungus that overwinters as small black structures (sclerotia) in plant debris or in soil. Sclerotia may survive up to 8 years. After a conditioning period of several weeks at 40°F in moist soil, sclerotia can germinate in moist soil when temperatures are 59°F to 65°F and produce a small, stalked, cup-shaped fruiting structure (apothecium; plural: apothecia), which releases millions of spores into the air. Sporulating apothecia can persist 5 to 10 days. Spores are forcibly ejected and a few may be blown up to a mile but most land nearby. Spores can survive two weeks. Spores can infect senescent tissue such as dying leaves or plant debris and then invade any healthy part of the plant it physically contacts. Moist conditions within the plant canopy favor infection. Rain, dew, and/or irrigation practices that keep foliage wet for long periods favor white mold development.
There are many other host plants, including bean, pea, lettuce, carrots, cabbage, parsnip, potato, sunflower, radish, other crucifers, and cucurbits. Dandelion (Taraxacum officinale) is a very susceptible weed host. Only grasses, cereals, and onion are not affected by white mold.
Symptoms The disease is mainly on aboveground parts, producing a cottony white mold. As leaves decay, small white bodies appear in the mold and gradually change from white to black as hardened sclerotia develop. The disease frequently occurs in storage. This organism can cause damping-off of seedlings. In mature plants, the disease appears as a basal rot of crown and petiole. Decay is watery and fairly rapid. It turns pink and later is covered with white mycelium. In later stages, the white mycelium is covered with hard, black sclerotia. Frequently found after black heart.
- Reduce humidity and high-moisture periods within the plant canopy and field.
- Provide adequate aeration within, and especially between, rows by increasing plant and row spacing or trimming celery foliage.
- Orientating the rows in the direction of prevailing winds is useful for white mold control if the placement of irrigation equipment allows row orientation.
- Time irrigations to allow drying of plant canopy before nightfall or use subsurface drip irrigation; keep the top 2 to 3 inches of bed dry.
- Apply sufficient nitrogen to meet crop demands, but avoid excessive fertilization that can lead to dense, lush plant growth.
- To reduce pathogen population within a field:
- Rotate with non-hosts (grasses, cereals, and onion) for 8 years to achieve best control, but for at least 2 years to reduce population of sclerotia.
- Deep plowing buries sclerotia but plowing later years may return viable sclerotia to the surface.
- Where feasible, field flooding during warm temperatures destroys sclerotia.
- Cull and clean celery before placing into sanitized containers for storage. Store at 32°F and prevent condensation.
Chemical control No fungicide listed is likely to control pink rot enough to justify the expense of application for this disease alone.
- Botran 75 WSB at 2 to 5.33 lb/A. Not registered for use in Oregon. Do not apply within 7 days of harvest. 12-hr reentry.
- Endura at 8 to 9 oz/A, at least one week apart. To limit the potential for development of resistance, do not make more than two (2) applications of Endura per season. The preharvest interval is 0 day. 12-hr reentry.
- Serenade Opti at 14 to 20 oz/A on 14-day intervals beginning 8 weeks before harvest. Applications can be made up to and the day of harvest. 4-hr reentry. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, 3 to 4 quarts/A as a soil drench (drip or chemigation) on 10- to 21-day intervals, or 2 to 4 quarts/A as a foliar spray on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
Note Rotting celery contains high levels of toxins that react in sunlight to cause severe dermatitis in fair-skinned workers. Persons working in celery in sunny weather should wear gloves, long-sleeved shirts, and long pants.