Your sour cherry has flowered beautifully, but shortly after, whole shoot tips wilt, turn brown and die, as if a flame had caught them. What looks like late frost is often Monilia blossom blight, an insidious fungal disease of stone fruit.
This article is the detail edition to the overview in Recognising fruit tree diseases. The key is to tell it apart from frost damage and reach for the secateurs in time.
How to recognise blossom blight
The damage picture appears exactly at flowering time and shortly after. First single blossoms wilt and turn brown. From there the fungus grows into the shoot, and the whole shoot tip, young leaves and all, dies. The wilted leaves often stay hanging on the twig instead of dropping, an important sign of recognition.
Responsible is the fungus Monilia laxa, a close relative of the brown-rot pathogen. It enters through the open blossom in damp, cool weather. Especially affected are sour cherries, above all the Sour cherry 'Morello', plus apricots, almonds and plums.
How to prevent it
Cut out affected shoots
This is the most important measure. After flowering, cut wilted shoots back generously, about fifteen centimetres into the healthy wood. Only that way do you catch the fungus, which already sits invisibly further down.
Dispose of the cuttings
Put the affected shoots and all mummified fruit in the residual waste, not on the compost. They are the source of the attack next year.
Keep the crown airy
In an airy crown the blossoms dry faster and the fungus finds worse conditions. How to prune the sour cherry correctly is in Pruning the sour cherry.
Choose tolerant varieties
Some sour cherry varieties are clearly less susceptible than the classic Morello. When planting anew on a rather damp site, a deliberate choice of a more robust variety pays off.
Looks like frost, but is a fungus. Cut the wilted shoots after flowering well into the healthy wood, and you stop the blossom blight.
The core rule against blossom blight
Frequently asked questions
Is it frost damage or blossom blight?
Frost hits all blossoms evenly in one night, blossom blight travels from the blossom into the shoot and leaves the wilted leaves hanging. If you cut into a wilted shoot and the wood is brown inside, it is usually Monilia.
How far must I cut the affected shoots back?
Generously, about fifteen centimetres into the visibly healthy wood. The fungus grows on invisibly, further than the damage reaches. Cut too short and it stays in the shoot and drives the problem on next year.
Which trees are especially affected?
Above all sour cherries like the Morello, plus apricots, almonds and plums. Sweet cherries are less susceptible. A damp, cool spring during flowering worsens the attack everywhere.
Is blossom blight connected to brown rot?
Yes, both are caused by closely related Monilia fungi. Blossom blight hits the blossoms and shoots in spring, brown rot the ripe fruit in late summer. Both you fight through pruning and hygiene.
Do I have to spray against blossom blight?
In the home garden usually not. Consistent cutting-out of affected shoots, an airy crown and tolerant varieties are mostly enough. Sprays at flowering are tricky, because they can also hit the pollinators.
