The GARDENA gardening expert
Dear Mr H.: Of course I have some ideas for you! Without seeing the tree, I would say that the main cause of the damage is a fungal infection of the leaves. Primarily, some sour cherry varieties (such as the morello cherry) are attacked by the monilia fungus, but you write expressly of dying leaves and not of dying shoots. Such fungal infections of leaves, like the shot-hole disease or cherry leaf spot (you can google images of such diseases to see if this infection is occurring in your garden) tend to occur more frequently if a tree is not correctly thinned out, and therefore its crown is poorly ventilated. In trees where the crown dries out very rapidly, fungal infections of the leaves occur less often, or less intensively. The garden surroundings of the tree should permit sufficient ventilation of the tree, to prevent it “suffocating”.
The shot-hole disease features many small, reddish to brown spots, which fall out as the tissue dies off, leaving holes in the leaf which look like shotgun holes.
Cherry leaf spot, on the other hand, reveals red-purple patches with blurred delineations on the tops of the leaves, and white patches with a reddish edge on the underside of the leaves.
Should it be the case, as I suspect, that your tree is suffering from a fungal infestation of the leaves, ensure minimisation of the infestation by having your tree crown professionally cut and thinned out, and by thinning out the surrounding plants. Remove the dropping, diseased leaves by putting them into your organic waste bin or digging them into the soil.
According to the official register of the plant protection agents currently approved for use in private gardens and small gardens, there is at the moment no plant protection agent approved for combatting the shot-hole disease or cherry leaf spot on sour cherry trees. However, broad-spectrum fungicides against fungal infestations on the leaves of fruit trees, such as the product Universal-Pilzfrei Baycor M (by Bayer Garten), can have an effect on leaf spot diseases. You would have to check this based on the effective spectrum stated for the respective agent – in case of “Baycor M”, I have already done some research for you; the effectiveness of this product on leaf spot is stated.
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