Brown Spots on my Newly Planted Spirea Plants? - Ask Extension
Hello,
I planted these goldmound spirea plants (about 24 of them!) (I live in E Lansing) and am noticing they have gotten all these brown spots and...
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Brown Spots on my Newly Planted Spirea Plants? #871663
Asked June 05, 2024, 9:05 AM EDT
Hello,
I planted these goldmound spirea plants (about 24 of them!) (I live in E Lansing) and am noticing they have gotten all these brown spots and some are developing large dead spots within them. They are getting watered from a sprinkler currently (so on top of leaves). We are gone most long weekends, so they have not been getting watered every day but do not seem to be wilted or like they aren't getting enough water.
How can I treat/support these plants back to healthy? They looked good when planted!
Clinton County Michigan
Expert Response
It appears that your spirea is infected with a couple of different fungal diseases...powdery mildew and leaf spot.
One of the most prevalent diseases affecting spirea plants is powdery mildew. This fungal infection appears as a white, powdery substance on the leaves, stems, and flowers of the plant. It thrives in humid environments with poor air circulation.
Generally speaking, powdery mildew does not cause significant damage to the plant, but it is unsightly. Treatment is usually not necessary. Fungal sprays will help prevent the spread of the disease to other leaves, but will not "cure" the leaves already infected. It looks like just about every leave on your plants are affected. Here is some additional information about powdery mildew:
https://extension.umn.edu/plant-diseases/powdery-mildew-trees-and-shrubs
Spireas grow well is relatively warm and dry conditions. They do not want wet leaves all the time or soggy soil all the time. That leads to root rots or fungal leaf diseases. Your spirea may be getting too much moisture from rain and overhead watering.
Never water overhead, i.e. sprinkling or hosing from above. Apply water to the soil at the base of the plant. Most plants grow well with about 1" of water a week. Supplement rainfall by watering your spirea only when at least the top 1/2 to 1 inch of soil has dried out.
Also, you should brush off loose leaves and remove and destroy dead leaves. Do not compost them! If you can do some thinning of the plants to improve air circulation it would be helpful. (I assume your plants are receiving full sun...spirea prefers that.)
Leaf spot is another common disease that affects spirea plants. It also is caused by various fungal pathogens that thrive in warm and humid conditions. Leaf spot manifests as circular or irregularly shaped spotson the leaves, which may have a halo-like ring around them. The spots may vary in color from light brown to dark brown or black. To identify leaf spot on your spireas, inspect the leaves for these characteristic spots. As the disease progresses, the affected leaves may become distorted or develop holes.
To control leaf spot, it is recommended that you remove and destroy any infected plant material. This may not be an option since your plants are so heavily infested, but any infected plant material you can remove will reduce the amount of pathogens that can continue to infect the plants.
Again, avoid overhead watering to reduce moisture on the leaves, as this promotes the spread of the disease. Applying a fungicide labeled for leaf spot control can also be beneficial, following the manufacturer’s instructions.
Finally, considering the amount of infection/stress your plants are under...if you have not done so, I suggest you give them a moderate amount of fertilizer...even liquid Miracle Gro will work. But do not overdo it as spirea do not need a particularly rich soil. It may help pull them out the the funk they're in and help them put out some healthy leaves. If you do get healthy new growth, use the fungal spray on it. Be sure to select one that the label says controls leaf spot diseases.
One of the most prevalent diseases affecting spirea plants is powdery mildew. This fungal infection appears as a white, powdery substance on the leaves, stems, and flowers of the plant. It thrives in humid environments with poor air circulation.
Generally speaking, powdery mildew does not cause significant damage to the plant, but it is unsightly. Treatment is usually not necessary. Fungal sprays will help prevent the spread of the disease to other leaves, but will not "cure" the leaves already infected. It looks like just about every leave on your plants are affected. Here is some additional information about powdery mildew:
https://extension.umn.edu/plant-diseases/powdery-mildew-trees-and-shrubs
Spireas grow well is relatively warm and dry conditions. They do not want wet leaves all the time or soggy soil all the time. That leads to root rots or fungal leaf diseases. Your spirea may be getting too much moisture from rain and overhead watering.
Never water overhead, i.e. sprinkling or hosing from above. Apply water to the soil at the base of the plant. Most plants grow well with about 1" of water a week. Supplement rainfall by watering your spirea only when at least the top 1/2 to 1 inch of soil has dried out.
Also, you should brush off loose leaves and remove and destroy dead leaves. Do not compost them! If you can do some thinning of the plants to improve air circulation it would be helpful. (I assume your plants are receiving full sun...spirea prefers that.)
Leaf spot is another common disease that affects spirea plants. It also is caused by various fungal pathogens that thrive in warm and humid conditions. Leaf spot manifests as circular or irregularly shaped spotson the leaves, which may have a halo-like ring around them. The spots may vary in color from light brown to dark brown or black. To identify leaf spot on your spireas, inspect the leaves for these characteristic spots. As the disease progresses, the affected leaves may become distorted or develop holes.
To control leaf spot, it is recommended that you remove and destroy any infected plant material. This may not be an option since your plants are so heavily infested, but any infected plant material you can remove will reduce the amount of pathogens that can continue to infect the plants.
Again, avoid overhead watering to reduce moisture on the leaves, as this promotes the spread of the disease. Applying a fungicide labeled for leaf spot control can also be beneficial, following the manufacturer’s instructions.
Finally, considering the amount of infection/stress your plants are under...if you have not done so, I suggest you give them a moderate amount of fertilizer...even liquid Miracle Gro will work. But do not overdo it as spirea do not need a particularly rich soil. It may help pull them out the the funk they're in and help them put out some healthy leaves. If you do get healthy new growth, use the fungal spray on it. Be sure to select one that the label says controls leaf spot diseases.
