Mahonia leaf spots and browning - Ask Extension
I have a large, well-established mahonia bush that was blooming beautifully just two weeks ago. It has suddenly developed brown spots on its leaves an...
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Mahonia leaf spots and browning #818514
Asked January 12, 2023, 4:00 PM EST
I have a large, well-established mahonia bush that was blooming beautifully just two weeks ago. It has suddenly developed brown spots on its leaves and total browning in some areas of the plant. Since it is winter, I concerned about pruning away the damaged areas. What is the best thing I can do for this plant at this time? Thank you very much for your help!
Montgomery County Maryland
Expert Response
There is no action you need to take since nothing will heal the damaged leaves and the event that caused the damage has likely passed. As long as the plant's roots and dormant buds are still healthy, it should gradually replace damaged foliage as growth resumes this coming season.
As to what caused the damage, it's hard to tell. This might be predominantly winterburn, which is caused by leaf drying in windy or dry-air conditions while soil moisture is temporarily frozen or the soil is too dry, but that tends to result in blotchy or leaf-edge drying and browning rather than distinct spots in the middle of the leaf. We see what appear to be both types of symptoms present, but we can't zoom-in on the photos enough to be sure. Did anything drip onto this plant from a sprayed tree or wall nearby? The spotting looks a bit like phytotoxicity, which is tissue damage caused by chemical exposure (even from substances like organic pesticides, since any pesticide has the potential for causing damage when conditions are right). Even if phytotoxicity occurred, the plant as a whole will probably be fine with no intervention as long as it wasn't exposed to a systemic herbicide.
If too much of an eyesore, it's fine to selectively trim off leaves now that are mostly or entirely brown. Mahonia doesn't branch much on each woody stem, so after pruning, new growth will either arise from the base (suckers from the roots) or from the tip bud higher on that stem (or from both points).
Miri
As to what caused the damage, it's hard to tell. This might be predominantly winterburn, which is caused by leaf drying in windy or dry-air conditions while soil moisture is temporarily frozen or the soil is too dry, but that tends to result in blotchy or leaf-edge drying and browning rather than distinct spots in the middle of the leaf. We see what appear to be both types of symptoms present, but we can't zoom-in on the photos enough to be sure. Did anything drip onto this plant from a sprayed tree or wall nearby? The spotting looks a bit like phytotoxicity, which is tissue damage caused by chemical exposure (even from substances like organic pesticides, since any pesticide has the potential for causing damage when conditions are right). Even if phytotoxicity occurred, the plant as a whole will probably be fine with no intervention as long as it wasn't exposed to a systemic herbicide.
If too much of an eyesore, it's fine to selectively trim off leaves now that are mostly or entirely brown. Mahonia doesn't branch much on each woody stem, so after pruning, new growth will either arise from the base (suckers from the roots) or from the tip bud higher on that stem (or from both points).
Miri
