Japanese maple disease

Question: Our Gwen's Rose Japanese maple has developed these grey scale patches on the branches and the leaves have started looking sort of whitish and dry. We make sure it has been watered during this drought. Any thoughts?

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 12, 2024, 2:15 PM EDT
response: The growths on the bark pictured are lichen, a harmless organism that is not responsible for any plant damage and which does not need to be removed. We can't clearly see the leaf symptoms you describe, but it could be powdery mildew, or an array of fungal leaf spot infections caused by Phyllosticta or a group of fungi whose infections are collectively called Anthracnose. While they can be an eyesore when extensive and cause some premature leaf death and shedding, those diseases usually don't significantly impact long-term plant health.  Making sure the plant is regularly monitored for watering needs is all you can do for now. If leaves fall before autumn, try to collect them and dispose of them so they don't harbor spores under the tree, though if some blow away or can't be collected, it's not going to doom the tree. (Spores can always blow into the area from other regions in a future year, and plant disease spread and severity is often influenced heavily by the weather.)  Miri

responder: The Question Asker Replied July 13, 2024, 7:35 PM EDT
response: Thank you so very much for your speedy answer about my maple. I will not worry about the lichen and will monitor my watering practices. I think the leaf damage may be leaf scorch from watering our lawn with the sprinkler during the heat of the day, it may have also hit the leaves. I usually try and water from the bottom, especially in this heat. It is a rough summer! Sent from my iPad On Jul 12, 2024, at 2:15 PM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 15, 2024, 10:26 AM EDT
response: You're welcome. Leaves wet by a sprinkler will not scorch in the sense of developing burn marks; the phenomenon called "scorch" in plants is caused by leaf desiccation damage, though either high heat, insufficient root moisture, or too much direct sun for plant species adapted to shadier conditions. Water droplets don't burn leaves in the sun, though if hot water from the hose (if it wasn't flushed-out first) contacting leaves certainly might damage them (though in that case, the resulting damage would probably look like they were melting, like sautéed spinach, which is how steam weeder tools kill weed foliage).  Miri

responder: The Question Asker Replied July 16, 2024, 3:24 PM EDT
response: Our redbud suddenly started shedding leaves. Any ideas, mites maybe? We contacted our tree service and that was his guess. Recommended spraying. Sent from my iPad On Jul 15, 2024, at 10:26 AM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 16, 2024, 4:45 PM EDT
response: Spider mites are a possibility, but we can't rule-out overlapping issues like drought stress and air pollution damage. (Some plant species are more sensitive to contaminants like ground-level ozone and aspects that create poor air-quality days. We don't know Redbud's level of vulnerability to this issue.)  We do not recommend spraying for mites in this situation. Not only will it require pesticides that could harm other organisms (though insecticidal soap or horticultural oil would be lower-risk), but it could worsen leaf damage, since even plant-safe pesticides can injure leaf tissue if it's already been heavily fed-upon or damaged in other ways. Plus, no pesticide should be applied during temperatures above 85 degrees, or plant tissue damage is almost certain to occur.  You could spray plain water if you wanted, as a strong blast from a garden hose (of course, let out any hot water first) aimed at leaf undersides might dislodge some mites, if they are abundant. Nothing will reverse the existing leaf damage, though, even if the original issue abates, since leaves cannot heal. (Next spring's leaves will be normal, since this won't carry over.)  Instead, just continue monitoring the tree for watering needs for now in this ongoing drought. You can rake-up the Redbud's leaves this autumn after they fall and dispose of them just in case they harbor a pest for next year, but that isn't too likely in this case and so it's not a great risk if you don't remove its fallen leaves for any reason.  Miri

responder: The Question Asker Replied July 16, 2024, 6:25 PM EDT
response: ﻿Wow! Thanks a million for getting back to me so quickly, allowing me to call off the scheduling of the spraying which apparently is not the way to go. We will keep raking up the leaves, watering and spraying water on the upper leaves which seem to be the most affected. I truly appreciate the expertise and quick answers each time I have reached out. You all are AWESOME!!!!! JanaSent from my iPad On Jul 16, 2024, at 4:45 PM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 17, 2024, 10:47 AM EDT
response: Thank you, and you're welcome!