Die-off of acres of Indian plums
This is a question that came up for the Master Gardener Volunteers, but we are at a loss - an absolute dead end.
The client and her neighbor share over two acres on wild (unlandscaped) land. Many of the trees/shrubs in that are are Indian plums. She, and the plums, have been there for 40 years, with no problems.
This year something is causing a massive die-off. She estimates over 90% of Indian plums are affected, but the other trees remain healthy. The leaves turn brown, but stay on the branches. There is no sign of a massive insect infestation. She brought in a sample of a plant that was drying, and while there were a few leaf hoppers, there wasn’t a whole lot of them. There did appear to be black spot on a few of the leaves, but she indicated that most leaves didn’t show black spot symptoms before they turned brown. Suckers continue to come up from the roots of the dead trees.
The references I can find say that, except for lacewings and leaf spot fungus (Cylindrosporium nuttallii) Indian plum is very disease and insect free. The leaves with black spot didn’t look like images of nuttallii leaf spot fungus, but that doesn’t rule it out.
Do you have any idea of what might be going on? I don’t know if a nuttallii infection could cause a die-off over two acres in a single summer. Should I suggest she take an affected leaf to have the fungus identified?
Any help to make us look less clueless would be appreciated.
Clackamas County Oregon