Cause Peyronellaea curtisii (formerly Stagonospora curtisii), a fungus that can survive for at least a year in dry leaf material. Fruiting bodies and/or spores may be carried on the bulb. Leaves and flower stalks may be injured as they push up between bulb scales. Under moist or humid conditions, spores infect the plant through these or other wounds. 'Naked ladies' (Amaryllis belladonna) are not as susceptible to infection.
Symptoms Small, red, raised or elongated spots will first develop after infection of leaves or flower stalks. Dark, brownish red spots also develop on flowers or bulb scales. Reddish brown pimple-like fruiting bodies (pycnidia) develop in necrotic areas. Infected leaves or flower stalks generally bend at the point of infection and may dry up without producing a flower.
Any injury to the plant will result in a reddening of affected tissue, so this disease may be confused with physiological problems or insect injuries.
- Avoid injuring the plant.
- Destroy or remove diseased bulbs and infected foliage.
- Provide ideal growing conditions such as a temperature of 60°F to 75°F. Do not overwater, fertilize once a week, and place where it will get plenty of light but not direct sunlight.
Chemical control Generally not recommended, though Captan has been shown to be effective.
Reference Smith, C.O. 1934. Inoculations of Stagnospora curtisii on the Amaryllidaceae in California. Phytopathology 25:262-268.