rainbow eucalyptus losing leaves this past week

Asked July 23, 2019, 12:43 PM EDT

Bought this tree as a plant in a planter from Saturday market 16 years ago. It is now about 3 stories high. In my back yard. Near a walkway. 5 ft form the garage. It started dropping it's leaves a week ago. has lost about 20-30 percent. they are brown and red, have black spots on them that are not removable. What do you think might be happening?

Multnomah County Oregon

1 Response

More info is needed to determine what is wrong with your ailing eucalyptus tree.
Please gather the following: A) several close-up photos of the affected leaves. Take clear pictures of both the top and the underside of newly / slightly affected leaves; the same for more advanced / more affected leaves; the same for seriously stricken leaves. B) photos of any cankers (localized scarring) on branches or twigs. C) Photos of the whole tree, so we can see the extent of the problem. D) Photos of the tree in the landscape--seeing the surrounding site and the condition of nearby plants, ground conditions, as well as the tree's relation to environmental factors (buildings, streets, dog runs, toxic waste dumps, you know, the usual.) Sharp cell phone photos are great, and can easily be emailed to our diagnostic volunteers at the various offices.

The other thing that would be useful would be your recollection of what has changed near the tree before the problem occurred. Was there a change is sunlight, as other trees have been growing, or were recently removed? New swimming pool or driveway work? Nearby lawn removed and replaced with something else? Anytime an existing, established plant suddenly shows signs of stress, that means something in the environment has changed. Far more plant health problems are caused by changes in the physical environment (abiotic problems) than are caused by biological agents. And when a new problem is caused by a pest or disease, it is most often triggered by some change in the environment that made that plant in its situation a better environment for the pest or disease. So what is different now than earlier in the life of this tree?

Although you could resubmit this information to us here at Ask an Expert, we recommend instead that you send the photos and other information to one of our three Master Gardener phone clinics in the tri-county area. Include your phone number, as the trained volunteers on duty will undoubtedly have follow-up questions for you. Check this website for contact info for each of the offices.
https://extension.oregonstate.edu/mg/metro/have-gardening-question

Finally, the bad news is that because eucalyptus are rare in this area (only a few species tolerate our winter temperatures --and our generally lower light levels) there is not a lot of diagnostic information about the many fungal and bacterial blights that can affect eucalyptus here. The good news is that partial and even full loss of leaves will not usually, of itself, kill or heavily damage the tree. Most trees can completely defoliate up to five times in a year before permanent damage occurs. Research by M.A. Dick and P.D. Gadgil on Eucalyptus Leaf Spots for Forest Pathology in New Zealand (2009) has this for it's opening statement: "All leaf spot diseases cause death of part of the leaf tissue and may cause leaf distortion. Severe infection may lead to early defoliation. Trees usually recover from defoliation and growth is seldom affected."

Summary: gather more information and photos, and get in touch with the trained diagnosticians at your local Master Gardener phone clinic.