Why Are There Spots On My Hydrangea Leaves?
Are you finding spots on the leaves of your beloved hydrangeas? Don't despair! Gardening expert Melissa Strauss will help you to diagnose and treat those spots, to have your shrub back in peak condition soon.
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Hydrangeas are some of the most gorgeous bloomers of summer. Their large, spectacular flower clusters wow and impress, making wonderful additions to the garden and cut flower arrangements. They also have some specific needs when it comes to care, and when something is amiss, they can become vulnerable to various environmental threats.
One of the first signs that something is going wrong with your hydrangeas is leaf damage. Spots, splotches, blotches, and discoloration of leaves is a sure sign that your hydrangea is dealing with some type of stress. What kind of influences can cause this damage, though, and what do we do about it? Let’s discuss.
The Short Answer
There are a handful of reasons that your hydrangea may be developing splotches on the foliage. The most common diseases for these shrubs are fungal in nature and result from poor watering practices. The spots could also be a result of bacterial infection, fertilizer burn, or pest infestation. Good plant hygiene and regularly inspecting your plants are the best prevention for all of these issues.
The Long Answer
If you notice unsightly blotches on your hydrangea leaves, don’t panic. Several things can cause this, and very few of them will cause lasting harm. Most of these problems only affect the foliage and will end in winter when the old foliage drops.
Some of the issues that can crop up involve plant hygiene, fungal, and bacterial diseases, as well as pests, and even fertilizer issues. Let’s go over some of the more common problems that can leave your leaves looking splotchy and sad.
Fungal Leaf Spot
Because they are moisture-loving plants, hydrangeas tend to be susceptible to fungal pathogens. The more common fungal diseases to affect this plant include cercospora, anthracnose, phyllosticta, alternaria, and rust. They each have a different appearance, and you can identify them this way.
Cercospera
Reddish-purple splotches with grey centers. Typically, it shows up on the lower foliage and moves upward. Rarely fatal to the plant.
Anthracnose
Irregular, circular brown spots on leaves, tends to begin close to the mid-vein. Spots grow into larger, more angular brown areas. Rarely fatal, it can be if left untreated.
Phyllosticta
Small water-soaked areas develop into larger, circular brown spots. Not aggressive, often occurs where cold damage exists.
Alternaria
Brown on the margins with yellow, chlorotic borders. Margins will become necrotic over time. Rarely fatal to the plant.
Rust
Rust-colored blisters on the underside of leaves and yellow spots on top. Some varieties are more resistant than others.
How to Fix It
By the time you see these diseases, it’s usually too late to eradicate them. However, most of them are strictly foliar and will go away when the shrub loses its foliage for the winter. There are ways to prevent these diseases that are effective if you keep on top of them throughout the season.
Most fungal pathogens are waterborne, and they find their way onto your plant as a result of overhead watering. Pair this with shaded areas, and you have a recipe for fungus. Watering with a drip irrigation system is very helpful, but in the absence of one, try to water only the ground, not the foliage.
Another way to prevent this type of disease is good overall plant hygiene. Make sure you clean up under the plant regularly. Don’t leave leaf litter underneath where it can contract these fungal diseases and bring them closer to your hydrangeas.
If your shrub isn’t getting enough air circulation, pruning the canopy can be very helpful. Allowing air to circulate and getting some sun exposure to the interior of the shrub is great for preventing these issues.
Bacterial Leaf Spot
The bacterial pathogen Xanthomonas campestris is another cause of leaf spot disease. These bacteria can affect nearly every species of hydrangea, although oakleaf tends to be the most common. This bacterial infection favors the warm, wet conditions of the late summer season.
The lesions left by X. campestris are reddish purple and appear as many small spots that eventually join into larger spots. They may initially be round, but as they grow and reach the leaf veins, they will take on an angular shape.
The most common method of transmission is water splashing from an infected plant. The disease only affects the foliage, so it will shed along with them in the winter. It is rarely fatal but can be unsightly.
How to Fix It
Ideally, if you catch this disease early, you can remove the affected foliage and slow or stop the spread. As with fungal diseases, good plant hygiene is key in preventing the disease. Be careful about inspecting any new plants you bring home, and keep a watch on leaves near the end of the summer.
As it only affects the foliage, this disease is unlikely to be fatal to the plant, but it can weaken an unhealthy one significantly. An over-fertilized hydrangea will be more susceptible to damage than one that has been cared for properly.
Fertilizer Burn
Over-fertilizing is another issue that can cause unsightly spots on your hydrangea leaves. These shrubs don’t need an exceptional amount of fertilizer. Three yearly applications will typically be enough. Once in early spring, late spring, and once during the summer.
Fall fertilizing can be too much for these plants, causing damage to the roots, which will manifest in the foliage. You may see scorched leaves with brown, dry margins and brown blotches. It can be easy to mistake this for problems arising due to underwatering. But if you’re keeping track of your fertilizing schedule, that should tell you what you need to know.
How to Fix It
Stay on top of your fertilizing routine and make sure you’re giving your hydrangea the right amount and type. A balanced formula made for this type of plant will do the job perfectly. A formula of 10-10-10 is ideal, and make sure to fertilize only in spring and summer.
Pest Infestation
Hydrangeas are appealing to many garden pests. While some prefer the flowers, others are more interested in the rest of the shrub. They set up camp underneath your hydrangea leaves and either drain them of nutrients and moisture or munch on the tissue. leaving spots and holes all over. Here are some of the culprits and their identifying damage.
Aphids
You know these guys. They are soft-bodied, usually green, yellow, or brown, and they can destroy your garden. Their feeding may cause yellowing or distortion of foliage. Their excrement, honeydew, provides a perfect environment for black sooty mold to grow, which can look like irregular black splotches.
Four-Lined Plant Bug
Punctures left by their feeding can cause brown, sunken areas which turn into holes. The damage is usually minimal and requires no treatment.
Japanese Beetles
Large green beetles feed on and skeletonize leaves. Defoliation can be damaging to the health of the hydrangea.
Rose Chafers
Skeletonized foliage. Very difficult to get rid of.
Spider Mites
The two-spotted type are most common. They leave freckling and stippling on the leaves, and fine webbing beneath. They cause the most damage to under-watered plants and have many natural predators.
How to Fix It
Cultural controls should be the first line of defense. Plant plenty of nectar-rich flowers in your yard to attract lacewings and ladybugs, as their larvae are voracious predators. Hand removal of affected foliage can be helpful in the event of a mild infestation.
Hand-pick beetles and blast mites or aphids with water in the morning, giving the foliage time to dry. As a last resort, insecticidal soaps and horticultural oils work to eradicate most pests, but they can also harm beneficial insects.
Key Takeaways
Keep your hydrangeas healthy and beautiful by maintaining good care habits, and inspecting them regularly. You can keep your beautiful bushes in tip-top shape this way, and enjoy those incredible blooms year after year.
