I have 3 prunus cistena shrubs. They are all turning brown (leaves) and shrivelling up and falling off. Please see attached photo. Can you help?
Purple-leaf sand cherry (Prunus x cistena) is vulnerable to several insects and diseases, so may live under 10 years. See, for example, Missouri Botanical Garden: Prunus x cistena, which notes that these nasties include the following “Trunk cankers and borers can be particularly harmful. Japanese beetles can do significant damage to the foliage. Potential additional insects include aphids, scale, leafhoppers, caterpillars and tent caterpillars. Potential diseases include leaf spot, die back, leaf curl, powdery mildew, root rot, honey fungus and fireblight. Spider mites may also be troublesome.”
It is not possible to diagnose what’s happening with your shrubs from a photo and brief description. You may want to consult an arborist in your community – see the list at Landscape Ontario.
However, one disease that comes to mind is fireblight, which I’ll summarize below, with information primarily from Horticulture for home gardeners. Fire blight in the ornamental home garden.
Briefly, with fireblight, leaves turn brown and crispy but stay on the shrub, making it look like the leaves have been burned by fire. The stems could look “hooked” and bent over, resembling “shepherds’ crooks”. The bacteria that cause fireblight remain in the shrub’s branches over the winter. Look for spots where the bark has been attacked (cankers), which ooze as temperatures increase. The ooze contains bacteria, which can be spread by insects, pollinators, wind, rain, humidity and dew. High temperatures and humidity are ideal for fireblight to thrive.
Fireblight can be managed, but not cured:
Monitor: In late winter, look at the shrubs’ branches for cankers – if you find any, prune them off. The most critical time is when the shrubs blossom – watch for the ooze and cankers and “shepherds’ crook” stems.
Prune: When the shrubs are dormant, prune afflicted branches around 30-40 cm beneath the canker, and continue to prune affected branches during the garden season. Prune as lightly as possible, as pruning stimulates new growth, which is more readily prone to infection.
Careful with fertilizer: Again, don’t encourage too much new growth, so fertilize lightly with compost, as needed.
Good cultural practices include making sure the shrubs receive adequate light, good air circulation (they should not be crowded together or with other plants), and water.
Dispose of infected plant parts in the regular garbage, do not compost or recycle these. Disinfect any tools you use on the plant.
See also an earlier post on Ask a Master Gardener. Purple sand cherry tree.
All the best with your shrubs!
June 8 2024