How to tackle this disease on an apricot tree

Question

We live in Vienna, Austria, very near the Danube river. We planted this apricot tree back in spring of 2015 as a small tree bought from a local nursery. It has been growing very quickly and was always very lush with leaves and flowers. Last summer (2017) it bore fruit for the first time, but the fruit did not ripen. This spring we decided to prune it a little bit to start shaping it to fit our needs in the garden. We pruned it in late March and by end of May we noticed the leaves shriveling and dying. Throughout the late spring and summer, the tree was bare, dropping dead leaves. Can you tell me what the disease is and what can be (if anything) done about it.

Thank you so much.

Photos:

Answer 1

I haven't got good news either I'm afraid. The absence of soft, soggy, oozing or rotting areas rules out bacterial canker, but you might be looking at a case of Silver Leaf fungal infection or Phytoplasmas infection, which has been a problem in your area for some years. Silver leaf can be caused by pruning cuts made at the wrong time of year - stone fruit trees are best pruned around May to try to avoid this problem, but it can happen anyway. Symptoms would have included a silvering effect on the leaves prior to their rolling and going brown and dying, with eventual dieback of the shoots and branches https://www.rhs.org.uk/advice/profile?PID=245.

Phytoplasmas infection is commonly known as European Yellows, though it may by now have some other name, and it's been the cause of a major decline in apricot trees in Italy, France, the south east of the UK and in your area since the mid 2000's. This article https://onlinelibrary.wiley.com/doi/full/10.1046/j.1365-3059.2001.00536.x gives some detail - leaves often remain dangling on the tree, rolled, and papery looking, but most fall prematurely, and any fruits formed remain small and do not ripen. Over time it kills the tree; so far as I'm aware, no inoculum has been found to treat/prevent the disease.

It would seem there is no treatment for either of these fungal infections, so I'm afraid it's probably necessary to remove the tree - if you want to wait and see what it does next year, then you could try, but remove the dead shoots back to live wood.

Answer 2

You should probably prepare for bad news. The tree shows signs of bacterial canker infection which is reinforced by your description of the onset of the problem. The infection enters through cuts, blossoms and tools used to prune. It is made more likely in areas with a cold climate not tempered by the proximity of large bodies of water. It can affect cherries and peach and apricot and particularly the latter which is more affected by cold and is more susceptible.

Outward signs are raised rough black lesions on an otherwise smooth bark, blossoms that fall off prematurely, and sudden death of what yesterday appeared to be perfectly vibrant shoots. The first two may not be visible, but the last is. The infection is spreading inside the tree from the top down, killing the sap transportation tissues.

The tree may try to send up new shoots from low down on the trunk where the tissues are still good, and may even send up water shoots from a rootstock, but eventually the tree does not grow at all. It probably means that your location is too harsh for tender apricots.

By all means get other opinions, but consider removing the tree as soon as possible, your neighbours might consider it a source of infection and start mumbling, and wait years before trying a stone fruit tree again. I'm sorry, this is the worst, I know. Consider maybe an apple tree, which is hardier?