Why Are My Peony Leaves Turning White

Have you noticed any whitened peony leaves? The cause is probably powdery mildew. Peonies are one of many plants that are susceptible to powdery mildew. Even while they typically don’t die from this fungus, it does weaken the plant, making it more vulnerable to pests or other diseases. Peony blossoms can become very unattractive when peony powdery mildew ruins them. Your best line of defense is to educate yourself about the causes of white powder on peonies and how to avoid this widespread issue.

Do I need to prune back peonies that have powdery mildew?

The first step in preventing powdery mildew on peony is to purchase or transplant only healthy, disease-free stock. According to the University of California Statewide Integrated Pest Management Program, the growing location should provide the peony with full sun, well-drained soil, and plenty of air circulation.

As soon as diseased leaves appear, remove and destroy them. To prevent powdery mildew the following season, trim unhealthy peonies back to the ground and clear the area of all debris in the fall. Trees should not be cut down completely since they won’t grow back.

Avoid overfertilizing peonies since it promotes weak new growth. To increase distance and airflow, divide peonies that are overgrown or congested in the fall.

How do you treat powdery mildew?

Are you curious about the white spot on your plant? A frequent issue in gardens is the fungus powdery mildew, which affects a wide range of plants and decreases the quality and yield of fruit and flowers.

What Is Powdery Mildew?

Numerous plant species are afflicted by the fungal disease known as powdery mildew. Each of the numerous varieties of powdery mildew infects a variety of different plants. Cucurbits (pumpkins, cucumbers, melons), nightshades (tomatoes, eggplants, peppers), roses, and legumes are some of the garden plants that are frequently impacted (beans, peas).

A layer of mildew made up of several spores develops on the top of the leaves when the fungus starts to take over one of your plants. The wind then spreads these spores to other plants. If the infection is serious enough, powdery mildew can stunt the growth of your plant and lower fruit yield and quality.

How Does Powdery Mildew Spread?

Powdery mildew spores often blow into your garden with the wind, but if you’ve previously experienced outbreaks, new outbreaks could potentially result from dormant spores in surrounding weeds or old vegetative material.

Even though it needs relatively high relative humidity (i.e., humidity around the plant) to spread, powdery mildew does well in warm, dry areas (60–80F / 15–27C). It does not spread as quickly in cooler, wetter locations, and it is also hindered by temperatures above 90F. (32C). Additionally, plants in shaded places are typically more impacted than those in broad sunlight.

How to Identify Powdery Mildew

  • Plants with powdery mildew infection resemble they have been flour-dusted.
  • On leaves, stems, and even on fruit, powdery mildew normally begins as round, powdery white patches.
  • The upper portion of the leaves are typically covered in powdery mildew, although it can also develop on the undersides.
  • The most vulnerable foliage is the young foliage. The leaves dry out and turn yellow.
  • Some leaves may twist, shatter, or become deformed as a result of the fungus.
  • The majority of the leaves or other damaged parts will be covered with the white patches caused by powdery mildew.
  • The growing tips, buds, and leaves will also develop defects. Typically, these signs show up at the end of the growth season.

Small white dots on the upper half of the leaves are the earliest signs of powdery mildew. The Regents of the University of California, UC Davis, provided the image.

How to Prevent Powdery Mildew

The best method of eradicating powdery mildew, as with many other diseases and pests, is proactive prevention.

  • For your garden, pick plants that can withstand powdery mildew. Cucurbits (melons, cucumbers, squash, etc.) have many mildew-resistant varieties that are available from major seed providers.
  • Plant where there is more sunlight because powdery mildew tends to grow more frequently in shaded regions.
  • To improve air circulation around your plants and lower relative humidity, selectively prune crowded spots.
  • Spores on leaves can be removed with the use of overhead irrigation. It’s best not to rely on this as a preventive measure, though, as moist foliage can frequently lead to the development of other common diseases.

Homemade Prevention

Powdery mildew can be effectively treated using sulfur, lime-sulfur, neem oil, and potassium bicarbonate, among other organic fungicides. These are most effective when used prior to infection or when you first see signs of the disease.

  • Many gardeners have demonstrated that baking soda works well to treat powdery mildew. Add 1 quart of water to 1 teaspoon of baking soda. Thoroughly mist plants because the solution only kills fungus that comes into touch with it.
  • A further efficient home treatment is milk spray. Spray roses with milk that has been diluted with water (usually 1:10) at the first indication of infection or as a preventative step.


There are several fungicides that are highly efficient with low toxicity, no residue, and long duration, especially for rose plants. Triadimefon is one case in point. It can be sprayed 1000–1200 WP of 15–% wettable powder once every 10 days for a total of 23 times. However, you should ask your neighborhood nursery about fungicides that are legal there.

How to Control Powdery Mildew

Concentrate on preventing the illness from spreading to other plants because it is very difficult to eradicate it if plants are severely afflicted. Remove and destroy any fruit, stems, or foliage that has been contaminated. You can either burn them or dump them in the trash. Any plant that has been affected should not be composted because the illness might still be carried by the wind and linger in the composted materials.

Avoid touching healthy leaves with pruning shears after removing sick areas. Pruners should first be cleaned with rubbing alcohol.

How is peony fungus avoided?

I’ve had peonies for a long time. Some of them were white, as though covered with mold, when I pruned them back this fall. Will the plant be affected the next year? Should I take any action in response to it? Do you understand what led to it?

A fungus called powdery mildew, which is the most likely source of your issue. Onset typically occurs from late June through September. The plants are usually not killed by this disease, but it weakens them and makes them more vulnerable to other pests and illnesses in addition to making them look ugly. The illness will have less of an effect on your plants the later in the season it arrives. In the spring, your plants should continue to bloom well.

Other plants that are susceptible to powdery mildew include lilacs, phlox, and bee balm. The white, powdery look of the leaves makes it simple to spot.

Depending on the temperature, powdery mildew outbreaks change from year to year. It’s not a guarantee that you’ll have an issue the next year just because one fall had a lot of powdery mildew. Peony cultivars vary in their susceptibility to powdery mildew, just like other susceptible plants. It is better to switch out a plant entirely or with a resistant type of peonies if you have one that is consistently deformed.

High humidity, moderate temperatures, and rainy weather are all factors that encourage the growth of powdery mildew. In the shade, when they receive overhead watering, and in areas with poor air circulation, such as those that are overgrown or crowded with other plants, plants are more susceptible to damage.

Prevention is key because once your peonies are infected, there is no spray that can treat them. The issue can be greatly avoided by choosing resistant cultivars and properly situating them in full light with sufficient air circulation.

Disease prevention can be aided by good cleanliness. The conclusion of the growing season is always the greatest time to remove sick plant foliage from the garden. If you see any sick plant portions, you might want to prune them out. But before you cut, consider how the plant’s appearance will be impacted by the pruning.

There are fungicides available to attempt and stop powdery mildew. However, the spraying needs to be done early in the growing season, before powdery mildew is visible, and it needs to be done again every 10 to 14 days. You can also try making your own fungicide by combining 1 teaspoon baking soda, 1 tablespoon horticultural or canola oil, and 1 tablespoon liquid dish soap in 1 gallon of water. Personally, I wouldn’t waste my time using fungicides to stop powdery mildew.

Botrytis is a different, more harmful disease that occasionally infects peony and causes young stems to droop and die as well as buds to become black. When it is below 70 degrees in the early spring, onset occurs. If this illness is discovered, it must be treated right once because it will damage peony plants. As soon as you notice unhealthy plant parts, remove them. To prevent the illness from spreading to more stems or other plants, make sure to clean your pruners between cuts with alcohol or Lysol disinfectant.

How can powdery mildew be avoided?

The following actions can be taken to prevent powdery mildew, therefore do them now:

  • To increase airflow within the plant, thin out any existing sensitive plants.
  • To guarantee optimum air circulation and aid in lowering relative humidity, maintain enough space between plants and keep them far enough away from walls and fences.
  • Place plants where they will receive the right amount of sunshine.
  • By eliminating damaged or diseased leaves, keep plants healthy.
  • After using pruners or shears on sick plants, clean them. (Read about tool care and upkeep.)
  • Be careful not to over-fertilize and encourage a rush of new leaves because new growth is more vulnerable.
  • Apply an organic fungicide with sulfur as its active component on a regular basis. This can be applied both as a prophylactic strategy and as a remedy for powdery mildew that already exists.
  • Pick plant kinds that are more resistant to powdery mildew when you go plant shopping.

Can you get rid of powdery mildew?

The good news is that most cases of powdery mildew infections are minor. With the right care to increase ventilation, otherwise healthy plants may frequently recover on their own after weather changes.

There are treatment methods available that do not include the use of traditional fungicides for serious infections or an issue that affects the entire garden.

Fungi may become resistant as a result of repeated usage of fungicides. The effects of this on agriculture and public health are both significant.

Cultural Controls

Most of you have likely experienced a rosemary plant that died from this disease. How could that be?

Often, it is obvious that you killed your plants by giving them a bit too much love and solving the issue incorrectly, usually by overwatering or underwatering.

The catch-22 in this situation is that stressed plants are more vulnerable to infection even if the fungus itself must survive on a living host and even though its objective may not be to kill your favorite rosemary.

If your plants are not given the right attention, you are doing them a disservice and opening the door to diseases, as well as other issues like pest infestations, a failure to produce beautiful flowers or high crop yields.

Cultural controls, which deal with alterations to the growth environment, are essential components of organic farming and integrated pest management (IPM).

Making adjustments to the soil’s pH or nutrient composition, watering more or less, and ensuring that plants receive the proper amount of sunlight are some examples of these.

Keeping plants healthy, content, and hopefully free of illness requires providing them with the right environment.

Although you might be able to nurse a tropical plant along through the fall in a cold climate, or you’re “only two zones away from what was indicated on the plant tag,” those recommendations are there for a reason. If you’ve been ignoring those USDA Hardiness Zones and recommended planting times for your region up until now, take heed.

In order to promote optimum airflow, cut foliage as needed. Damp, crowded foliage is more prone to infection.

In general, sun is the enemy of fungal illness, so be sure to provide plants with as much sun as they require to thrive, whether that be shade, partial sun, or full sun.

Some experts advise watering overhead to prevent this illness, but others strongly advise against it because it would increase the humidity inside the plant. Such an increase in humidity may promote infection or worsen an already present ailment.

Follow our instructions and be sure to never wet the leaves while watering plants; always water at the soil line. Since plants will have time to dry off before nightfall, watering early in the day is often preferable to watering at night.

Powdery mildew is more prone to infect lush, recently produced tissue. As a result, avoid nitrogen fertilization in the late summer and always be mindful to prevent overfertilizing your plants with this nutrient if you have a problem with this disease in your garden.

If your plants are contaminated, remove and destroy the diseased tissue. The virus can spread to other areas of your garden if you put it in your compost pile.

Plant material and surrounding weeds may both act as hosts for dormant spores. Keep your garden borders and beds weed-free and spotless.

Some growers who raise their crops in greenhouses syringe the leaves of vulnerable plants with water during the day when humidity is low, said Dr. Gary Moorman at the Penn State Extension. Given that the spores won’t germinate in the presence of water, this has been demonstrated to be an effective way to prevent powdery mildew infections.

However, this method can significantly raise the likelihood that the plants will develop other diseases, like fungal leaf infections. We don’t advise it.


Spraying milk on plant parts that exhibit symptoms will aid in controlling powdery mildew, especially if done at the beginning of an illness.

Many organic farmers utilize this method, which has been proven successful in research on tomatoes, grape vines, apples, pumpkins and other winter squash, cucumbers, zucchini, and other types of plants over the course of more than 60 years.

The above-mentioned study on pumpkins and acorn squash demonstrated that applications of compost tea were ineffective, but this widely accessible product could give control comparable to that attained by the use of traditional chemical fungicides. Early on in the infection, milk treatment was most beneficial.

The usual recommendation is to spray your plants with milk that has been diluted 1:10 with water as soon as an infection appears.

You can use liquid or powdered milk. The data that is currently available suggests that greater milk concentrations might be the most efficient.

For moderate to severe infections, try a 50/50 mixture of liquid milk and water, or even full-strength milk if you don’t have a lot of space to treat.

Although some experts advise against using whole or 2 percent milk because of their fat content, others maintain that it doesn’t matter what kind you use.

Fill a spray bottle with the liquid, then use it to treat the damaged portions of your plants, including the stems and the undersides of the leaves. Apply twice weekly until you start to see benefits, and don’t forget to reapply after rain.

Though the spray can acquire a sour smell in the hot heat, milk spots on plants’ leaves shouldn’t be a concern (less unattractive than the mildew, at least, if you do notice any). Of course, this is preferable to having ill plants on your hands.

Sodium and Potassium Bicarbonate

Since the early 1930s, scientists have tested the efficacy of baking soda (sodium bicarbonate) as a fungicide and discovered that it is ineffective on plants, despite being able to stop the formation of mold in a laboratory.

It might help prevent rotting of harvested fruits and vegetables, according to Dr. Linda Chalker-Scott, Associate Professor of Plant Pathology and Extension Specialist at Washington State University.