Hydrangea Botrytis Blight Disease: Treating Gray Mold On Hydrangea Plants

Hydrangea Botrytis Blight Disease: Treating Gray Mold On Hydrangea Plants

By: Bonnie L. Grant, Certified Urban Agriculturist

The bold flowers of hydrangea are a true summer treat. The plants are rarely bothered by pests or disease, although hydrangea botrytis blight can occur. The first signs are discolored flower heads followed by gray mold on hydrangeas. This is a serious disease and can cause damage to the flower buds.

Signs of Hydrangea Botrytis Blight

During cool, damp periods an opportunistic fungus may invade your garden. It is hydrangea gray mold, but it doesn’t confine itself just to that genus. Botrytis blight may also attack other ornamental plants. A hydrangea with botrytis will have its flowers attacked initially and as the disease progresses, the foliage will suffer. It’s important to your plants to learn how to diagnose and control this damaging disease.

The fungus Botrytis cinerea starts to appear on the flower buds. The first sign is a fuzzy mold-like growth. The flowers and buds will brown and wither and begin to drop. Once this happens, the spores of the fungus come in contact with the leaves. Water soaked tissue appears and gradually extends to become brown, round to irregular spots.

Once a few flowers have the disease, it can rapidly spread to the entire plant. Usually, initial infection is in the interior flowers and those lower down that do not have adequate circulation.

Controlling Gray Mold on Hydrangeas

Botrytis cinerea is common when the weather is cool and rainy, generally in early to late spring. In a greenhouse, the problem can become an outbreak. In open spaces, the fungal spores can still spread from plant to plant. That includes many other ornamentals, fruits, and vegetables.

The fungus overwinters in dropped plant debris. Plants that grow in shade and are overcrowded are most commonly affected. It is important to clean up any plant debris in such locations to prevent infection.

Before you even have a hydrangea with botrytis, you can take steps to prevent its occurrence. In addition to cleaning up plant debris around the hydrangea, prune the plant so that it is open and can receive air into the interior. Avoid planting groups of hydrangeas too close together.

If the disease has already occurred, nip off any affected flower heads and discard. Use a fungicide in early spring to prevent spores from taking hold. Products containing neem oil, potassium bicarbonate, Bacillus subtilis, or chlorothalanil are effective.

This article was last updated on

Read more about Hydrangeas


How to Prevent and Get Rid of Gray Mold

It seems that there is no shortage of pests and diseases that want to wreck all of my hard work in the vegetable garden this year.

Where I live, it has been an unexpectedly hot and dry year. While that means we were lucky enough to not have to deal with fungi, it meant that we were subjected to a whole host of other problems. From tomato hornworms to blossom end rot, we really struggled to get a handle on things!

Gray mold on some strawberries. Photo by Rasbak – Own work, CC BY-SA 3.0, Link

Fortunately, those problems have more or less subsidies, and we are still enjoying a bountiful harvest from our plants nonetheless. Another benefit of the warm, dry weather was that we didn’t have to worry too much about a problem we’ve had in the past – fungal disease.

Gray mold, also known as botrytis, is one of the most common fungal diseases in the backyard vegetable garden. It is common in cucumbers, tomatoes, and green beans, along with some fruits like blueberries, strawberries, and raspberries. Flower gardeners, you aren’t immune – it can even affect African violets and some species of succulents!

Gray mold can be devastating to a garden, but luckily, there are some steps you can take to cut it off before it becomes a problem. Here’s how to prevent and get rid of gray mold before it drives you insane!


How to Prevent Hydrangea Diseases

Hydrangeas delight the eyes with spectacular and showy blooms, rich foliage, and long-lasting beauty in the garden. Unfortunately, diseases like powdery mildew and leaf spot can afflict the plant and dim their glow. This guide will help you prevent and identify any ailments your flowers may have.

TIP: Our expert gardening advisor Susan Patterson suggests, "Grow disease resistant varieties of hydrangea for best results."

Powdery Mildew

Powdery mildew appears on the bottoms of lower leaves. It looks like small, circular white patches with feathery edges . The upper leaves may also show purple or yellow blotches. As the cottony mildew spreads and the stalks are destroyed, it can cause stunted and off-color foliage as well as smaller, discolored blooms.

TIP: Susan advises, "Always clean pruning tools in hydrogen peroxide before using."

Plants under stres s, especially in conditions with high humidity , are prone to powdery mildew.

  • Regularly water your plants
  • Feed with a well-balanced fertilizer
  • Add mulch
  • Ensure the hydrangea has good air circulation and is not planted too close to other plants

If powdery mildew is already present, buy a good fungicide from the local nursery to combat the disease. Remove dead and diseased hydrangea leaves to control the spread of the disease and to give the plant a chance to regain its health.

Leaf Spot

Landscape and container-grown hydrangea plants can develop Cercospora leaf spot. This disease affects bigleaf, oakleaf, smooth and panicle hydrangea. It won’t kill the plant, but it does diminish the plant’s health and result in fewer buds and an unsightly appearance,

The first sign is brown or purple circular spots on leaves at the base of the plant. Heavily spotted leaves often turn a yellow-green color and fall to the ground. As the diseased leaves fall, they spread the infection to the rest of the plant. Remove the diseased leaves and apply nitrogen to help slow the development and spread of the leaf spot.

To control leaf spot when it first begins, apply a fungicide according to the instructions on the package. Do this especially with highly-valued plants that succumb to the disease every year.

Other Hydrangea Diseases

Hydrangea is susceptible to several other diseases. Here is a brief listing of what they are and how to treat them:

  • Anthracnose – Hot, wet weather conditions help foster development of this disease that normally affects heavily-fertilized hydrangeas. Brown spots appear, grow in size and spread over the plant. To prevent, apply a protective fungicide at 10 and 14-day intervals through the summer. Promptly remove diseased, fallen leaves and blighted flowers.
  • Botrytis Blight – A gray mold, this disease primarily affects the bigleaf hydrangea. It is promoted by cloudy, humid weather. It can appear overnight. Start fungicide treatments when plants begin to bloom and continue throughout summer.
  • Mushroom Root Rot – Common to landscape plantings, this disease most affects oakleaf hydrangea. To prevent, water thoroughly during summer drought and fertilize according to instructions. Fungicides will not prevent this disease, and affected plants must be completely destroyed.
  • Phytophthora Root Rot – Reduce risk of this disease by planting hydrangeas on raised beds amended with 3 to 4 inches of aged pine bark or compost. Fungicides can prevent, but will not cure, this disease.


Control and Prevention

How to Control Gray Mold

  • Remove the infected plants and destroy them.
  • Clean thoroughly between your plants so that the disease cannot infect your other plants.
  • You can try using sprays with cultural controls on your plants to prevent further infections.

Prevent Gray Mold

  • Handle your plants carefully when transplanting and pruning. Gray mold usually attacks wounded plants, so avoid harming your plants.
  • Keep your plants dry. Avoid overhead watering and watering late in the day. Give your plants time to dry off after watering them during the day.
  • Space your plants properly to encourage good air circulation.
  • Remember to clean between your plants. Remove any debris, including cuttings and dead leaves.

Leaf Spots

Multiple fungal pathogens including Cercospora can cause leaf spots on hydrangea. Spots vary in color, size and shape, depending on the responsible pathogen and they type of hydrangea. Severely affected leaves often drop prematurely. Healthy hydrangeas can tolerate some degree of infection. Pruning off isolated, heavily infected portions of they hydrangea when conditions are dry can help to prevent spread. Promptly raking up and disposing of fallen leaves is important. Chemical control is rarely necessary, but a preventative treatment with a copper compound may be warranted where leaf spots were very severe on particularly prized or visible hydrangeas in previous years.

Rust, like leaf spot diseases, is caused by a fungal pathogen. Spores spread via wind or splashing water to hydrangea leaves. Rust appears on foliage as masses of dry, orangish spore pustules primarily on leaf undersides while the upper leaf surface turns yellow or brown. Infected hydrangea leaves may drop early. Avoid overhead watering or inadvertently wetting hydrangea foliage with sprinkler irrigation, as wetting the foliage encourages spore germination. Prune off and dispose of infected leaves promptly.


Botrytis Blight

Botrytis blight often strikes when you least expect it. Plants are doing well, flowers are attractive and plentiful, and growth seems vigorous. Then spots appear, plants decline, and rot and mold occur. Activity for this disease peaks during cool, damp seasons, but infections may occur all year round. Poor air circulation, high humidity, and overcrowding aid its spread by wind, rain, or irrigation.

Botrytis blight affects many popular plants, including beautiful garden roses, tasty tomatoes, beans, geraniums, and petunias. Leaves, buds, stems, flowers, petals, and fruit are all potential targets for this widespread disease.

Botrytis Blight Identification/Symptoms: The earliest symptoms of botrytis blight are often brown spots on leaves and buds, or spots of dark color on flower petals. As the disease progresses, flowers and fruits rot, and spots begin to show fuzzy, grayish mold.

Botrytis blight is one such fungal infection where you eventually see the offending fungus, not just the symptoms of the underlying disease. Masses of dust-like gray fungal spores develop on dead and dying plant tissue where they're easily seen.

How to Control Botrytis Blight: Once botrytis blight becomes active, it's more difficult to control. Prompt action is crucial. This disease often enters plants through small wounds and moves quickly once it starts. Preventive application of fungicide early in the season helps prevent botrytis blight infections and halt their spread.

GardenTech ® brand's highly effective Daconil ® fungicides offer three-way protection to stop, control, and prevent botrytis blight and more than 65 other fungal diseases. Start preventive treatments whenever conditions are ripe for disease, or treat at the first hint of symptoms. These products can treat tomatoes right up to the day of harvest or treat beans up to seven days before harvest time:

  • Daconil ® Fungicide Ready-to-Use provides the perfect option for treating containers, individual plants, or small garden spaces. Shake the sprayer container and it's ready. Spray all upper and lower plant surfaces until they're thoroughly wet.
  • Daconil ® Fungicide Concentrate simplifies protecting larger garden areas from botrytis blight's threat. Measure concentrate into a hand-held, hose-end, or tank-style sprayer with the convenient measuring cap. Then add water, mix well, and spray until all plant surfaces are thoroughly covered.

Botrytis Blight Tips: If botrytis blight hits your garden, immediately remove diseased plants or prune affected stems back into healthy tissue. Sterilize your pruners with household disinfectant after every use to prevent the spread of disease. Keep your garden tidy the fungus can overwinter in plant debris.

Always read product labels thoroughly and follow instructions, including guidelines for treatable plants and pre-harvest intervals (PHI) for edible crops.

GardenTech is a registered trademark of Gulfstream Home and Garden, Inc.

Daconil is a registered trademark of GB Biosciences Corp.


Watch the video: Brown Spots on Hydrangea Leaves