Question
I've had my flowering peach tree for 5 years.at the end of last year i noticed the tree is turning a black color.(bark).looking at it closer it has just started to bud which is good,the black substance will scrape off with my nail.any clue what this could be.

Answer
Dear Nigel, The black sooty substance on the bark of your tree is caused by some insect.  It could be scale, which is a non-moving insect that lives under hard shell like structures and secrete a honeydew like liquid that becomes sooty.  It could be whitefly which also makes the honeydew although the immature insect is in a scale on the underside of the leaves, and the adults will fly in a white cloud when you shake the branches.  Aphids are also a culprit for this soot, and the last possible cause would be powdery mildew which first turns the leaves whitish then will turn to black and can cover the bark as well.  Personally, I think the most likely cause would be the scale.  Either way, the cure for this is the same.  You will need to spray the tree thoroughly with a horticultural oil, and the black will simply flake off.  Be sure to spray the tree thoroughly several times about 5-7 days apart.  The good news is that this is very safe, very effective, and won't affect the peaches.  The bad news is that you can't spray the tree while it is in bloom.  So if the buds haven't opened yet, you can spray; if not, absolutely don't spray until after the blooms are all gone.  There are several reasons for this.  If you spray with open flowers, it will affect the bees, the flowers will be destroyed (and not pretty) and the flowers won't get pollinated and make peaches if they are sprayed.  It won't affect the tree much to wait until after the flowers are gone, and your fruit will still develop.  Since you are so far north and it has been a very cold winter, you may be able to spray now.  I hope this information helps.  Good luck, and write back if you have more questions.  Melissa