Maple tree with white specks - Ask Extension
We have a younger maple tree in our front yard that is not doing well. Upon inspection the newer growth is turning a dark green / brown. All leaves h...
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Maple tree with white specks #878025
Asked July 20, 2024, 1:16 PM EDT
We have a younger maple tree in our front yard that is not doing well. Upon inspection the newer growth is turning a dark green / brown. All leaves have white smooth spots, only in the tops of the leaves.
The maple tree is around 20 feet tall. It’s gets 40 min of watering with sprinkler system every other day.
Please see attached photo.
Is this an aphid? Scale? Fungus? How can we best treat this issue?
Thank you!
Ottawa County Michigan
Expert Response
Thank you for your inquiry, Abigail. The white spots on your maple leaves appear to be a fungal disease called Powdery Mildew. In mid-late summer, nights begin to cool and the sun isn’t as intense as it begins to move south. These changes can also bring an unwanted guest: powdery mildew. Most gardeners have seen it and may not know what it is. It looks like someone sprinkled powdered sugar all over your plants, but it’s actually
a fungal infection. There are many species of fungi that cause powdery mildew infections, and most are specific to one type of plant. In other words, powdery mildew on your maple will not spread to other plants in your garden ... except for another maple tree.
You mentioned that the tree is watered every other day by a sprinkler. Wet leaves, especially if they don't dry off during the day and remain wet overnight is an invitation to fungal diseases. When watering your tree, you should lay a trickling hose near the base of the tree for an hour or two...a couple of times a week should be adequate. If we have sufficient rainfall, even this watering should not be needed. If your sprinkler is hitting the lower leaves of your maple tree, powdery mildew is bound to occur. The spores of the fungus is spread then throughout the canopy of the tree by wind and rain.
While the white spots are unsightly, this disease generally does not do a lot of harm to the tree. Fungal sprays will not "cure" this disease, but it might help prevent further spread. Effective spraying of a 20' high tree is untenable anyway. The best thing to do to prevent this disease next year is to rake up and destroy the fallen leaves from the this tree in the fall. Do not compost them or leave them lying around as the spores will overwinter on the fallen leaves.
Regarding the "browning" of your leaves, I do not see that in your pictures. What I see are very dark leaves that may be due simply to an overabundance of moisture. Considering that we've had quite a rainy summer so far, extra moisture on this tree could be causing the leaves to turn dark. If there were a disease or insect problem causing browning, the brown areas would be light-to-dark brown-to-black and crispy...they would look dried out. I don't see that.
If this were my tree, I would stop or greatly reduce watering your tree for awhile and see if it perks up. The link below will give you information about powdery mildew.
https://extension.umn.edu/plant-diseases/powdery-mildew-trees-and-shrubs
a fungal infection. There are many species of fungi that cause powdery mildew infections, and most are specific to one type of plant. In other words, powdery mildew on your maple will not spread to other plants in your garden ... except for another maple tree.
You mentioned that the tree is watered every other day by a sprinkler. Wet leaves, especially if they don't dry off during the day and remain wet overnight is an invitation to fungal diseases. When watering your tree, you should lay a trickling hose near the base of the tree for an hour or two...a couple of times a week should be adequate. If we have sufficient rainfall, even this watering should not be needed. If your sprinkler is hitting the lower leaves of your maple tree, powdery mildew is bound to occur. The spores of the fungus is spread then throughout the canopy of the tree by wind and rain.
While the white spots are unsightly, this disease generally does not do a lot of harm to the tree. Fungal sprays will not "cure" this disease, but it might help prevent further spread. Effective spraying of a 20' high tree is untenable anyway. The best thing to do to prevent this disease next year is to rake up and destroy the fallen leaves from the this tree in the fall. Do not compost them or leave them lying around as the spores will overwinter on the fallen leaves.
Regarding the "browning" of your leaves, I do not see that in your pictures. What I see are very dark leaves that may be due simply to an overabundance of moisture. Considering that we've had quite a rainy summer so far, extra moisture on this tree could be causing the leaves to turn dark. If there were a disease or insect problem causing browning, the brown areas would be light-to-dark brown-to-black and crispy...they would look dried out. I don't see that.
If this were my tree, I would stop or greatly reduce watering your tree for awhile and see if it perks up. The link below will give you information about powdery mildew.
https://extension.umn.edu/plant-diseases/powdery-mildew-trees-and-shrubs
