First symptoms include pale yellowish lesions and watery soft spots. These affected areas are soon covered with characteristic blue-green spores. Fleshy scales may show water-soaking and a light tan or gray color when affected bulbs are cut open. As decay continues, bulbs may become soft and tough or may develop a watery rot. A musty odor is usually present.
Conditions for Disease Development
Penicillium spp. can be found in soil, on plant and animal debris or on senescing tissues. Infection of bulbs is usually through tissues damaged by bruising, freezing injury or sunscald. The pathogen grows well at 21-25°C (70-77°F) and under moist conditions.
A minimum of bruising and wounding of bulbs during harvest and prompt drying of harvested bulbs is recommended. Low temperature, approximately 5°C (41°F), and relative humidity are recommended for storage. Fungicide treatment of bulbs can be effective in controlling this disease.