Posts Tagged ‘gray mold’

Botrytis infected peony stem and bud

An ugly name for and ugly disease!

Botrytis or gray mold is a fungal disease that attacks many perennials but especially peonies – the “aristocrat” of the spring perennial garden!

A peony bud and stem infected with botrytis

A peony bud and stem infected
with botrytis

Anyone who grows peonies eagerly anticipates the appearance of their glorious blooms in mid to late May. Sometimes we are bitterly disappointed when our peony stems suddenly begin to turn brown, wilt, and flop over.

It is especially upsetting when this occurs after the flower buds have developed and are beginning to swell on the stems. We can hardly wait for them to open and reveal their beautiful flowers – but then … Ugh!


Botrytis at the base of this peony leaf

Botrytis at the base of this peony leaf

Botrytis blight often rears its ugly head in the garden after late spring freezes or during periods of cool, rainy weather. It can be especially damaging to plants when wet, humid conditions persist over several days.

Botrytis (Botrytis paeoniae) is probably the most common disease of herbaceous peonies. It typically first appears as brown or black patches on the bases of the young leaves and stems when they emerge in the spring. The stems and leaves wilt rather quickly and fall over.

This peony bud would have produced a beautiful flower!

This peony bud would have produced
a beautiful flower!

A gray mold which produces and disseminates a tremendous number of spores eventually develops in these areas. These botrytis spores are carried by the wind and also by insects to the leaves and flower buds of other nearby peonies where they grow and cause leaf blight and bud rot. Often, this is when the damage becomes most noticeable. The very tiny flower buds turn black and fail to develop further while larger buds and the stems just below them turn brown and quickly droop over. Unfortunately, under favorable conditions, botrytis can quickly spread through your peony beds unless steps are taken to control it.

What can you do?

Botrytis spores beginning to cover this diseased bud.

Botrytis spores beginning to
cover this diseased bud.

If you notice botrytis on the buds, leaves, or stems of your peonies, carefully remove the infected plant tissue, place it in a bag and discard it in your trash – do not put it in your compost pile! Never prune infected stems and foliage while the plant is wet or you risk spreading the disease to other healthy plants.

Botrytis overwinters in dead leaves and other plant tissue so it is important to remove all plant debris from the garden in the fall. Cut peony foliage to the ground in September or October, bag it up, and put it in the trash. Rake up dropped leaves and remove them from the garden.

Again, do not compost any of this plant debris.

Leaf blight caused by botrytis often develops after the blooming period.

Leaf blight caused by botrytis often
develops after the blooming period.

In the spring, just as the shoots begin to come up, spray the shoots and the surrounding soil with a mixture of Bonide Mancozeb (with Zinc) and Immunox according to the label directions. Then begin a spray program, spraying first with Mancozeb, copper fungicide, or Bonide Fung-onil and then 10 days later spray with Immunox or one of the other fungicides that you didn’t use for the first spray. Repeat this every 10 days until they flower.


In our gardens, botrytis wasn’t too bad this year. However, I have had a few calls about the sudden death of peony buds or the lack of bud development all together. If you don’t see signs of botrytis, the following are a few other reasons why peonies might fail to bloom:

  1. A late spring frost or freeze might kill the buds. We had some very cold nighttime temperatures this spring. It dropped into the mid 20’s several times in the middle of April and we even had frost in mid May this year.
  2. Peonies may be planted in too much shade. Sometimes, as your landscape matures, full sun gardens can become more and more shaded. Peonies will bloom in bright shade but the bloom will begin to decline in deeper shade.
  3. Too much nitrogen will hinder flower development. Your grass loves lots of nitrogen; peonies, not so much. Nitrogen promotes lush green growth – just what you want for your lawn but not your perennials. Foliage comes at the expense of flowers. Be very careful to keep your high nitrogen lawn fertilizer out of your perennial beds if you want a nice show of flowers! Choose an organic fertilizer like one of the Espoma “tones” or another fertilizer that is lower in nitrogen.
  4. Bare root peony showing the two types of "eyes".

    Bare root peony showing
    the “eyes”.

    Your peony may be getting too old. As your peonies get age, flowering may slow down. To rejuvenate your peonies and make them bloom well again, dig and divide them in September or October when the foliage begins to turn brown. Here are some tips.

  5. Peonies are planted too deeply. Plant your peonies so the eyes are no deeper than 2″ below the soil surface. If they are planted deeper than this, they may not bloom.

Our peonies were pretty spectacular this year! I hope yours were, too!

Peony 'Gay Paree' blooms in the Viette gardens. It is one of Andre's favorites.

Peony ‘Gay Paree’ blooms in the Viette gardens. It is one of Andre’s favorites.

If you don’t have any planted in your garden, maybe it’s time to find a sunny spot for one or two! Check out our list!

Until next time – Happy Gardening!

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