It sounds like you may have Blossom Wilt or Brown Rot on your cherry tree. This causes the flowers and fruit to wither and die. Leaves may also shrivel and there may be die-back of the shoots. Prune out any infected branches/blossoms and put the clippings in with normal household waste (don’t compost or recycle them). Pruning improves air circulation around the branches. Spray your cherry tree with a systemic fungicide such as Westland Plant Rescue Fungus Control (containing Difenoconazole). Start applying it as the flowers open next year, following the instructions on the label.
The most common cause of this type of damage is the fungal infection Brown rot. It appears particularly during wet a wet season causing small brown spots on the flower petals, stems and fruits where it normally where the spores enter the plant through minor lesions. As it the fungal infection progresses it causes sunken brown cankers on twigs where the rotting fruit touches them, and rings of grey spores on the rotting fruit. The fruits will eventually shrivel and become mummified, remaining on the tree over winter. The spores overwinter in the fruits and stem cankers before releasing more spores the following year.
It is too late to do much about it this summer but in autumn you should collect up all of the infected fruits from the tree and the ground and destroy them. Once the leaves have fallen you can also take a look at the stems and prune out any cankers that might harbour spores over winter.
In spring, you can also try spraying the tree with a fungicide at the beginning, peak and end of flowering. Use a fungicide that contains the active ingredient difenoconazole such as Westland Plant Rescue Fungus Control. Hopefully this will clear many of the spores before next years crop develops.
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