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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.

  • Full blooming or just few flowers? – Giacomo Catenazzi Oct 4 '17 at 14:20
  • @GiacomoCatenazzi The apple is full blooming, the walnut is on its way. I have posted an update. – Alina Oct 4 '17 at 14:31
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Copper sulphate could be applied in autumn, in spring (better) or in both periods (e.g. on zones prone of fungal diseases).

Now with flowers, it is difficult to apply it where the diseases is hiding because of petals, and because of "fold" on gems. So I would wait, and if weather turn really bad, you can do an additional one in spring.

What to do with blooming? This is the most complex part of the question, and I don't have really an answer. Late flowers help diseases to spread, so I was told to remove them, but this was in case of few flowers. Personally I got a late full blooming only on Laburnum and it survived (the cause: extreme dense climbing weeds), and almond tree never care to bloom the right period. IMHO it indicates a grave problem. Sulphates will not help.

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