Controling Powdery Mildew on Peonies


“how to get rid of the white podwer on the leaves of my peonies? ~Paula”

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Hi Paula,

Thank you for the email via Facebook regarding the fungus on your peonies (Paeonia suffruticosa).  Sounds like you have a case of Powdery Mildew.  Powdery mildew is a white, fluffy buildup on both the top and underside of leaves, eventually resulting in leaf death and loss. Powdery mildew infests numerous types of plants, including peonies.  It is not considered as serious a threat on peonies as other plants; however, powdery mildew seems to be increasing as an issue with peonies with the weather conditions we have had this year.

Adequate spacing and thinning discourages powdery mildew development and
spread among plants. Place peonies at least 4 feet apart. Water the roots, avoiding extended periods of moisture presence on flowers and leaves. Prune heavily infected areas, and avoid using high nitrogen fertilizers that promote new growth, which is especially susceptible to powdery mildew development.

For chemical treatment, use fungicides as soon as powdery mildew appears on
peonies to limit damage and protect nearby peonies.  Chemical sprays such as
Benomyl (systemic fungicide) or sulfur/fungicidal soap early in the growing
season as a preventative or as soon as symptoms appear. A synthetic
fungicide Baylaton sold as Strike also works well on mildew. Powdery mildew
can develop resistance to every fungicide except sulfur. Apply sulfur to
peonies only on days when the temperature remains below 85 degrees
Fahrenheit, because sulfur damages plants in high temperatures.  No matter
which fungicide you choose, always follow label directions to make sure the
product is approved for peonies.

For organic treatment, depending on the severity, spraying it with a baking
soda formula is effective as a preventative when applied regularly.  For
active infections spray daily for a week.

1. Mix 1 Tbsp each of  baking soda  and horticultural oil (dormant
oil/vegetable oil) or a few drops of liquid soap to 1 gallon of water.
Spray weekly making a new mix each time.  It will not eliminate the disease
but help control it.

2. Mix 1 tsp baking soda with a few drops of vegetable oil in 1 quart of
water. Spray or paint on the leaves.  Works on houseplants, cucurbits &
roses (black spot).

Another suggestion is  a solution of 1/3 milk and 2/3 water and spray on
plants. Use every other day.

Neem Oil is also effective in controlling infections. Use 1 oz.(2 Tbsp) of
Neem oil and 1/ 1/2 tsp of dishwashing detergent to one gallon of water.
Spray once a week for two weeks.  The combination of Neem and baking soda
treatments is the safest control method. Once the disease takes hold, it is
difficult to control.

 

 

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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6 thoughts on “Controling Powdery Mildew on Peonies

  1. Peony plant, approx.20 yrs. Never ever had a problem in growth all these years. This year just in the past 4-6 weeks after flowring and removing, I now have mildew which when hosed, is removed. But I also have some sort of black spots, 1″ or so.
    Does this plant have to be removed permanently? what else to do.
    Garfield, NJ

    • The color of the spots and the texture are very important in determining if you have a minor or major disease. If the spots have a reddish coloration, it is a minor fungal infection. There are many different types — they are generically referred to as leaf spot and are a from having a cool, wet year.

      The mildew that you talk about makes me think that the most common problem would be Botrytis cinerea. It attacks stems, buds and leaves. This disease can appear at any time of the growing season, but is most common in cloudy, rainy weather. It begins early in the spring when the shoots are about six inches tall. Young stalks discolor at the base, wilt, and fall over. This wilt and shoot death may continue throughout the summer if conditions are wet. Other symptoms during the growing season include large, irregularly shaped spots on leaves and brown flower buds that are covered with a mass of gray, fuzzy fungal spores. The fuzzy fungal spores, produced after rain or watering, are characteristic of Botrytis infection.

      Good sanitation (including prompt removal of spent flower blooms) and following the cultural recommendations above will greatly reduce Botrytis problems. Fungicides are of limited effectiveness against this disease, but basic copper sulfate or Mancozeb can be applied early in the season when shoots are about six inches tall to help protect the plant. Spray all plant parts to thoroughly wet foliage and soil. Read and follow all label directions.

      If the spots are definitely black or brown and have a leathery texture, then it is Phytophthora cactorum, may be confused with the symptoms produced by Botrytis sp. The stems, leaves, and buds can be affected by both diseases. However, with Phytophthora blight, there is no felty growth or sporulation on the plant surface when in a wet environment. Infected parts become dark brown or black and somewhat leathery. The entire shoot may turn black and die. Cankers may appear along the stems and cause them to fall over. While Botrytis sp seldom invades the crown, Phytophthora sp often does, causing a wet rot to develop and destroy the entire plant. Because infections of this disease generally occur in the roots and lower portions of the stem, spraying with fungicides is of little value. Confirmed cases should be removed and destroyed, together with adjacent soil. Planting healthy clumps in new locations where the soil is well drained usually prevents further trouble.

      I’m hoping it is one of the first two, as you will be able to save the plant.

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