Branch die-back on Mexican Blue Oak - Ask Extension
Our neighbor and friend planted a Mexican Blue Oak from Cistus Nursery in August of 2020. It's healthy looking overall, been watered deeply approxima...
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Branch die-back on Mexican Blue Oak #785689
Asked March 31, 2022, 4:45 PM EDT
Our neighbor and friend planted a Mexican Blue Oak from Cistus Nursery in August of 2020. It's healthy looking overall, been watered deeply approximately every 3-4 weeks during the dry months, and has put on 2-3 feet of growth since being planted. Planted in full sun in clay loam soil.
Recently, our neighbor noticed a number of branch tips look dead on the last 2-4 inches, with leaves browned out. Some of the leaves also have what look to be fungal spots on their surfaces and rings of dead tissue around them. Bark and branches show no weeping, discoloration or splitting.
Any idea of what's happening here and if there's anything that should be done? (i.e., remove dead leaves, branch tips, change watering regimen, or ???)
FWIW, there was a Silver maple in the same spot that was removed in early summer 2020 due to verticillium wilt causing large branches to die off.
Multnomah County Oregon
Expert Response
Trying to grow a broad leaf evergreen native to high elevation, arid regions is going to be difficult in a low elevation, wet environment such as the Willamette Valley. It seems this tree has gotten a good start but management may need to be adjusted for continued health. I hope it was planted into a very well drained soil/media. That will help during our wet winters with increase in rainfall. Watering will have to be adjusted as well to account for vary conditions. I am sure it will not like a lot of water on the roots.
Water on the leaves will encourage a lot of fungi that these plants may not have seen before. Some of those leaf spots look much like fungal infections but that is a guess. There are so few diseases reported on this host. None that match the images you have included.
Have a look around at Madrone trees in your area? A similar type of plant out of its native arid environment. They look terrible this time of year with multiple leaf spots and some defoliation. They will look better once the new leaves pop out soon and the older leaves are cast off.
Which brings me to some of the leaves you show in your images. Some of those look to be normal senescence and will naturally fall off. Evergreens just are not. Older leaves will be cast away normally. This does not explain all the leave issues but may explain the older leaf loss.
Water on the leaves will encourage a lot of fungi that these plants may not have seen before. Some of those leaf spots look much like fungal infections but that is a guess. There are so few diseases reported on this host. None that match the images you have included.
Have a look around at Madrone trees in your area? A similar type of plant out of its native arid environment. They look terrible this time of year with multiple leaf spots and some defoliation. They will look better once the new leaves pop out soon and the older leaves are cast off.
Which brings me to some of the leaves you show in your images. Some of those look to be normal senescence and will naturally fall off. Evergreens just are not. Older leaves will be cast away normally. This does not explain all the leave issues but may explain the older leaf loss.
