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This is a silhouette of my two plums:

enter image description here

They are very old, around 10m high, for some longish time left alone, and exude a lot of sap. They have nice fruit. Birds like to rest and observe the area in their high crowns.

Is there anything I can do to revitalize them? Or just leave them as is?

VividD
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  • When you say they emit a lot of sap, what does that mean? Where is the sap coming from? – Bamboo Dec 12 '17 at 16:07
  • From the trunk. @Bamboo – VividD Dec 12 '17 at 16:09
  • hmm, well a photo of the area of trunk that's leaking sap would be helpful. Is it leaking amber coloured sap, or clear? – Bamboo Dec 12 '17 at 16:21
  • Amber. @Bamboo There are also several holes with average diameter 8cm in the trunk, made obviously by birds. – VividD Dec 12 '17 at 16:36
  • Sounds like gummosis, which may or may not be fatal... photos would be good. Gummosis can be a major problem if there's bacterial (rather than viral, which it probably isn't) involvement, some reading here http://www.100flowers.win/Article/questionandanswer/plantdiseases/201608/2634.html, but photos would still be good. One question though - do you have tree borers in your country? (we don't in the UK, but they do in the States and other places) – Bamboo Dec 12 '17 at 18:23
  • If birds are making holes in the bark then there is a bigger problem to consider. Wood peckers aren't doing trial and error holes. They know that breakfast is right below the bark. I would get a horticulturalist or arborist out to look at your trees. You've probably got some bark beetle slowly killing your trees. – stormy Dec 13 '17 at 05:00
  • The title of the question is 'revitalizing', not 'killing'. – VividD Dec 13 '17 at 10:51

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If the sap they are exuding is gelatinous in consistency (and my answer is making that assumption), then it means they have a fungus which is highly contagious to other stone fruit trees. I think you best option would be to cut the trees down, and plant non-stone-fruit trees or wait 3 years and then plant plums of your choice.

Escoce
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  • Is 'gelatinous in consistency' = 'consistently gelatinous'? Also, I have no idea how to tell if sap is 'gelatinous'. :) – VividD Dec 12 '17 at 18:49
  • If the tree dies, would the virus dissapear? – VividD Dec 12 '17 at 18:51
  • Does it look like water or does it look like gelatin? Water makes the tree look wet, gelatin will be thick. The virus will remain in the ground for a few years, you are advised not to plan another prunus tree there for at least 3 years. – Escoce Dec 12 '17 at 19:06
  • More like gelatin – VividD Dec 12 '17 at 19:07
  • Then the trees have the virus. I would have them removed and have the stump removed too if you plan on planting more prunus after waiting a few years – Escoce Dec 12 '17 at 19:08
  • @Escoce - I never heard of this virus - can you provide a link or give its name, please? – Bamboo Dec 12 '17 at 19:17
  • @Bamboo Forgive me, I was wrong it's not a virus but fungus. Google "peach tree gelatin" for results including the following in gross paraphrase, "Cytospora canker, Valsa canker, Coryneum Blight, the fungal cause of gummosis, affects stone fruit trees like apricot, cherry, peach, and plum." – Escoce Dec 12 '17 at 19:24
  • Erm, I guessed you mis-spoke - its clear its gummosis, as I say above in the comments, but what's not yet clear is whether is pseudomonas, cytospora or any of the others, need photos for that. Its also not necessarily infectious to other trees... – Bamboo Dec 12 '17 at 19:39
  • If I leave the trees as snags, will the source of infection disappear in three years (just as in the case of roots)? – VividD Dec 12 '17 at 20:07
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    No, the fungus incubates in the dead wood and sends spores out into the air in the spring. – Escoce Dec 12 '17 at 20:09