A friend of mine has an apple tree and a walnut tree that have bloomed for the second time this year. The trees grow in a 6b hardiness zone in the Northern hemisphere where it is already autumn. Night temperatures are 7-9°C (44-48°F). A sour cherry tree that bloomed last year in autumn has died during the following winter and the owner fears that this year the apple and the walnut tree will follow the same path.
An old man that runs a seed and pesticide shop that knows other people having had the same problem in the past few years told me that the only thing to do is to apply copper sulphate after the first hoar-frost, not sooner. Will copper sulphate not only protect from fungal infections during dormancy, but also help the tree to go dormant?
In the next 10 days the weather forecast estimates the same night temperatures, except for tomorrow night when there will be 15°C (59°F). Should my friend wait for the first hoar-frost and apply copper sulphate or is there something else to be done?
Update: The apple tree is full of flowers like it was spring, except for a branch that is in the shade.
The walnut tree doesn't have flowers yet, but the buds are on their way to open in a few weeks. Its leaves have more than 15 cm (6 inches) in length.