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I have a pair of lilacs, very close together, which have been fine for ten years. This year they have hardly any leaves (just patches of them) and what appears to be a whiteish and partly yellowish mold on the trunks. It looks like some kind of mold disease.

Can anyone identify the disease and tell me what I should do? Or are they only fit to be cut down.

I have other lilacs on the other side of the house that are fine. This is in Southern Ontario.

trunk bark wood

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Looks like two sorts of lichens; generally regarded as harmless to the tree. I have not yet found any reports showing them to be bad for trees.

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The two lichens I'm spotting here are Xanthoria Parietina and Foliose lichen. They are harmless and very common to find on tree branches.

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  • Do you have any suggestions for other things I should be looking at as to why they have hardly any leaves? – DJClayworth Jul 4 '20 at 21:23
  • The reasons that come to my mind are: proper pruning, extreme temperature changes, soil quality, watering, other pests. The leaves from your picture seemed undisturbed so I don't think you have a pest problem. – Persistent Plants Jul 5 '20 at 17:11
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Lilacs love limestone. In my area the geology changes suddenly from limestone to granite and while in the limestone areas you can't stop the lilacs from growing and blooming profusely it is really hard to achieve the same thing on granite. So soil quality, in particular acidity/alkalinity (pH) is the first consideration.

Second the existence of much lichen (as already identified by others) indicates moist growing conditions. If the lilacs that you have that are fine do not show the same population of lichens try to figure out why conditions might be so much wetter for some bushes.

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