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Brown Spots On Hydrangeas – Causes & Treatment

Hydrangeas are popular among many homeowners due to their big clusters of beautiful blue, pink, and white flowers that blossom in the summer. This flowering shrub usually comes in different varieties, hence why its leaf shape and flower color differ.

Nevertheless, all these varieties have one thing in common, and that is a common enemy, which is fungal infections, bacteria, and pests.

In this article, we’ll discuss several fungal and bacterial infections that often cause brown spots on hydrangeas. We’ll look at what steps to take to address this issue and ensure your garden maintains a striking look.

Cercospora Leaf Spots on Hydrangeas

Cercospora leaf spot on hydrangeas

This is a common infection that results in brown spots on the hydrangea leaves and is caused by the leaves regularly being in contact with water either due to irrigation or rain.

It usually starts as either a purple or brown spot on the plant’s leaves near or close to its base. These spots, which have a diameter of 1/8” to 1/4”, are tiny and appear scattered throughout the leaves.

Furthermore, these spots on the hydrangeas start developing gray or tan centers, which are then engulfed by purple or brown halos.

If nothing is done to contain this infection, the leaves eventually yellow-green and drop. However, incidences of the Cercospora leaf spot killing the target plant are extremely rare.

But, severe leaves spotting as well as premature leaf shed may lead to a reduction in the flower bud and plant’s vigor that occurs during the season. Additionally, this leaf disease also results in a hideous look at the hydrangeas plant.

Prevention and control of Cercospora Leaf Spot

There are a few things you can change about the landscape of your garden to either slow down or altogether prevent the spreading of the Cercospora leaf spot. These include:

  • You should try and avoid splashing water on the hydrangea leaves instead of watering the plant’s base. Moreover, even as you water the soil, only do so in adequate proportions, thereby ensuring the water surrounding the roots is moist rather than continuously wet or soggy. This is vital as this later results in several harmful plant infections, including root rot. Thus, instead of watering your hydrangeas plant with a little water daily, you should consider reducing the frequency in which you deep-soak it. Doing this is essential as it allows the soil to dry in between the watering periods.
  • Get rid of all the heavily spotted or dead leaves and dispose of them.
  • Consequently, apply a tree type and shrub fertilizer on the hydrangeas plant as this helps maintain its steady growth rate. Nonetheless, you should stop using the fertilizer after two months before the average first frost date around your region.

The occurrence of the Cercospora leaf spot illness usually does not show up until it’s between mid and late summer. Therefore, you should use a protective fungicide to spray all the areas where you notice the signs of this infection to control its spread.

Additionally, if the plant suffers from any visible damage each year, you need to use a copper-based fungicide as this helps treat this condition.

To effectively treat this disease, you need to start the treatment either early summer or late spring when the symptoms start showing. Finally, check the product label to have an idea about the mixing and application guidelines.

Hydrangeas Anthracnose

hydrangea Anthractnose

Anthracnose usually occasionally appears in the landscape and typically infects only the bigleaf hydrangea, which some people also know as “French” hydrangea or “mophead.” This leaf disease creates big snowball-shaped clusters of flowers with shades of white, red, pink, or blue.

Whereas this infection is mostly prevalent in big field plantations or greenhouses of carefully managed hydrangea, outbreaks can also reach residential areas and affect your garden. The fungi responsible for this disease are the Colletotrichum Gloeosporioides, which can attack the hydrangea blooms and leaves.

The conditions that favor the spread of brown spots on the hydrangeas plant are wet, hot weather and heavily fertilized plants are also more prone to this infection.

The first sight of the brown spots on hydrangeas is somewhat irregular and circular and slightly sunken on the plant’s fleshy leaves. At the center of these leaves, these spots may reach a diameter of one inch or more and subsequently start changing in color from light brown to tan.

Moreover, slightly lighter and alternating rings of dead tissue usually make the spots have a target-spot or bull’s-eye look. Subsequently, when more prominent spots border either the midvein or any other main vein on the leaf, they start showing a more distinct angular shape.

If the ideal conditions for the development of this disease persist, the big, irregular, dark brown spots will quickly spread across the flower petals and leaves of the hydrangeas. Finally, the symptoms of this infection sometimes appear almost at once on both the blooms and leaves in the upper and lower areas of this plant.

Prevention and control of the Anthracnose

There are several measures you can take to counter the spread of this infection, and this includes:

  • Collect all the fallen infected leaves and then take out the destroyed blooms as recommended.
  • Secondly, you should avoid splashing water on the leaves while watering the plant and instead direct the water towards the plant’s base area. As you water the plant, you need to ensure you do so in reasonable proportions to make the soil moist rather than continuously wet or soggy. This is vital as this helps prevent the development of other detrimental plant infections like root rot. Moreover, you should also consider not watering your plants daily and instead consider deep soaking them less often to allow the soil to dry in between the watering.
  • Lastly, it would help to use a copper-based fungicide to spray both the flowers and the foliage according to the given directions. Additionally, you should spray both the foliage and blooming flowers the following summer before the brown spots start showing on the hydrangeas.

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Hydrangea Rust (Pucciniastrum Hydrangea)

Hydrangea rust (Pucciniastrum hydrangea)

Diagnosing this leaf disease is rather straightforward as it looks unique compared to some of the most common infections prevalent across plant leaves. When the leaves of the hydrangeas get infected with this disease, the formation of yellow spots starts on the top side and orange spots below. As time passes, the color of the leaves will eventually become brown and then fall off.

Controlling this disease is quite challenging; however, it can be managed by thoroughly cleaning all the sick debris and leaves that have already fallen from the hydrangeas plant. Subsequently, thin the inner side of the hydrangea once you are done disinfecting the pruning shears.

Additionally, if you suspect that rust is likely to be persistent, you should instead opt for the cultivar “Frosty”, which is more resistant to this infection.

How do you treat hydrangea rust?

This leaf disease usually spreads due to the splashing of water on the hydrangea plant leaves, which mostly happens as you water the plants.

Therefore, while watering, you should always confirm that you are spraying the water towards the plant’s base to try your best and ensure the leaves above remain completely dry.

Likewise, you can also remove all the disease-infested leaves if the condition is not very serious, and this will be enough to prevent the spread of rust. However, if the issue is severe, you may need to use fungicide for this disease.

Hydrangea Leaves Edges Turning Brown

Hydrangea leave edges turning brown

Hydrangea plants that have either been planted recently or a growing in a pot are often susceptible to intense fertilizer use. Subsequently, because of this, you may start to notice the leaves gradually turning yellow and eventually brown around the edges and the tip a day or two after applying the fertilizer.

Also, the roots of this plant may have suffered from slight burning. Furthermore, Aluminum sulfate, which occasionally gets added to the soil, changes the hydrangea blooms color and causes root damage if you apply too much of it.

How do you treat the leaves edges of the hydrangea plant turning brown?

If you are looking to treat the brown spots from your hydrangeas plant, you need to flush the soil surrounding it with water regardless of whether it is on the ground or in a pot.

Doing this removes almost all of the salts found in the soil. Consequently, you should not water your hydrangea plant for about one or two days to ensure the soil on the surface is somewhat dry. After that, you should go ahead and start watering your plant as normal.

Nonetheless, if you have your hydrangea plant growing from the container, confirm that all the water drains from below the pot after completing each watering. This is vital as it will flash out the salts regularly.

Additionally, you should only fertilize your hydrangeas plant after a root burn once the plant looks healthy, as this is an indication that it is now healthy and the root system is well-developed.

Powdery Mildew Showing on the Hydrangea Leaves

Powdery Mildew showing on the hydrangea leaves

This is also another reason for the appearance of brown spots showing on hydrangea leaves. Fortunately, identifying it is easy as it starts with having a powdery, pale gray coating.

It usually spreads through spores from one plant to another, meaning it can quickly spread if proper measures are not taken to contain its spread. The spores generally transfer during cold nights and hot days, and big swings in temperature are a significant factor that aids the spread of this disease.

Some of the causal agents of this infection include Golovinomyces Orontii, Oidium Hortensiae, Microsphaera Friesii, Erysiphe Poeltii.

How do you treat powdery mildew on the hydrangea leaves?

The best technique of getting rid of this fungus is by taking off the infected leaves or any other part of the plant. You should only remove the whole part of the plant that the disease affects if the issue is severe.

As you water the plant, make sure only the base is getting watered to prevent the leaves from getting wetter, thereby quickening the spread of these fungi.

Moreover, you should make a point of watering in the morning as this gives the leaves the chance to have a whole day of drying before the temperature levels drop later during the day. If you are looking to kill the fungus, use an organic treatment and carefully follow the written instructions to ensure it is effective.

Hydrangea Leaves Becoming Yellow

Hydrangea leaves becoming yellow

During hydrangea’s growing season, that is summer or spring, the leaves sometimes suddenly turn yellow and brown. Subsequently, they start falling off, and the reason for this infection usually is an infection is a problem with the plant’s roots.

It frequently happens before the plant has had enough time to develop a deep and robust root system, for instance, before the hydrangea is transplanted from the pot or immediately after that.

The three most common causes of this happening include;

  • The plant is continuously kept very wet
  • The plant has become very dry
  • The plant has gotten plenty of fertilizer

Any of these reasons can result in the death of either a part of the entire root system. Once the root system has been destroyed, the leaves start to wilt, turn yellow and eventually brown.

Apart from these symptoms mentioned above, keeping your plant extremely wet also results in rotting and eventual death.

How do you treat yellow leaves on this plant?

Once you allow the plant to dry completely, you first need to water the whole root system exhaustively. If you still have the hydrangea inside a pot, place it in the water tub and rim it up until every dry root has been soaked in water entirely.

Consequently, let the plant drain completely. Because the roots are damaged, they cannot deal with the soil as it is incredibly wet. Therefore, you should give it time between every watering period to make sure the soil dries out marginally and hence allow the regeneration of the roots.