Cherry leaf spot (Blumeriella jaapii) is one of the most serious diseases of ornamental cherries in the landscape. The disease mainly affects the leaves, but lesions may also appear on fruit, petioles and fruit stems (pedicels). Diseased leaves drop prematurely, and severely affected trees may be defoliated by mid-summer. Early and repeated defoliation can result in a decline in vigor, which combined with buried root collars, girdling roots, and poorly drained soils can lead to premature decline.
Treatment Strategy
Collect and destroy the fallen cherry leaves in late autumn. The fungus overwinters in these leaves
Select a planting sight that is always exposed to direct sunlight, has good air circulation, and soil drainage. Proper pruning to open the canopy will increase sunlight penetration and air circulation. Any practice that promotes faster drying of leaves will reduce the risk of infection.
This disease can be controlled with fungicide sprays.
Foliar Spray Using Pegasus 6L
Signs of Damage
- Small circular purple spots appear on the upper surface of the leaf in spring
- Spots gradually enlarge to about ¼ inch in diameter and turn reddish-brown
- Centers of the spots may dry up and drop out, giving a “shot-hole” appearance
- With heavy infection older infected leaves turn yellow and eventually drop
- Lesions may emerge to produce large, irregular spots. will be microscopic.
- Whitish-pink masses of sticky spores (conidia) form within the spots on the undersides of infected leaves during periods of damp weather
Purple spots and early shot hole appreance
Late season defoliation
Trees At Risk
Ornamental flowering cherries (Prunus spp). Common cultivars:
- Yoshino
- Kwanzan
- Okame
- Autamnalis
Biology
- The fungus overwinters in dead leaves on the ground. In early spring (about petal fall), fungal fruiting bodies called apothecia develop in these leaves
- Spores (ascospores) discharged during rainy periods for about six to eight weeks
- Small purple spots soon appear on the upper surface.
- Under damp conditions and with temperatures between 60 and 68 degrees F (15 and 20 degrees C), lesions may appear in five days
- Once lesions have developed, masses of secondary or summer spores (conidia) are formed, causing new infection under ideal temperature and wetness conditions
References
The Ohio State University
https://ohioline.osu.edu/factsheet/plpath-fru-40
Canadian Journal of Plant Science
https://cdnsciencepub.com/doi/full/10.1139/cjps-2015-0362#.W9cNkdVKi00
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