Katie Goldenhar – Horticulture Pathologist
Anthracnose of garlic has been reported to infect only garlic scapes and bulbils. This disease has been observed in multiple northern US states including New York, Maryland and Indiana. In the early summer of 2022, lesions were seen on garlic scapes in Ontario (Figure 1). These lesions were orange, and sunken and spores were seen as a mat on the lesion surface as weather conditions were conducing to sporulation. The disease was confirmed using microscopy (Figure 2).
This is the first confirmed report of anthracnose of garlic scapes in Ontario. The disease is caused by the fungal pathogen Colletotrichum fioriniae, which has a wide host range. This pathogen can cause disease in apples and pears (bitter rot) and celery (leaf curl). Colletotrichum fioriniae has also been reported to infect and survive on numerous common weed species.
Temperatures from 25°C–30°C are optimum for disease development. Sporulation is triggered when at least 12 hr of leaf wetness have occurred. Spores are moved by splashing during rain or irrigation. Driving winds can move spores, but in general, spores do not travel well in wind. People and equipment can easily spread spores across fields and to other fields. Colletotrichum fioriniae can overwinter as mycelium on infected plants. Bulbils can be infected and result in the spread of disease. Overwintered mycelium can infect scapes the following spring.
Anthracnose of garlic does not seem to affect bulbs. If scapes are removed for consumption, scape yield may be reduced. The disease will negatively affect bulbil production for propagation.