Identifying and Treating Black Spots on Peony Leaves

Peonies are prized for their sumptuous, romantic blooms that burst forth each spring. But discovering inky black spots marring the leaves of your beloved peony can cause alarm. While frustrating, black leaf spot diseases are common and treatable if caught early. Arm yourself with knowledge of the culprits, symptoms, and care strategies to protect your peonies’ health and maintain their floral display.

What Causes Black Spots on Peony Leaves?

Two fungal diseases are the usual suspects behind black peony leaf spots:

• Botrytis blight – The most prevalent peony problem, botrytis blight thrives in cool, wet weather. It first appears as olive green spots on emerging shoots and buds. Spots then enlarge, darken to blackish-purple, and are often surrounded by a yellow halo. Entire shoots can blight, leaving no blooms.

• Phytophthora blight – More aggressive than botrytis blight phytophthora causes inky black spots stretching down stems to leaves. It can kill whole plants by rotting crowns and roots.

While botrytis is more common, phytophthora is more concerning due to its lethal potential. Catching and treating black leaf spots early is key to protecting your peony’s health.

When Do Black Spots Appear on Peonies?

The timing and location of spots can help identify the specific disease

• Botrytis – Spots emerge in early spring on new shoots and buds.

• Phytophthora – Spots appear after bloom time in early summer, spreading down stems to leaves.

Botrytis interferes with spring flowering while phytophthora emerges after blooms fade. But both can weaken and potentially kill peonies if untreated over time.

How to Treat Black Leaf Spot Diseases on Peonies

Fortunately, management of peony black leaf spot diseases is straightforward:

Remove Infected Foliage

Prune away all spotted shoots, leaves, and buds. Bag and dispose of this debris in the trash, not the compost pile. Both diseases overwinter, so cleanup is critical.

Improved Air Circulation

Give peonies good spacing and avoid overcrowding to allow airflow around plants. This reduces humidity supporting fungal diseases.

Spring Fungicide Application

Spray emerging shoots with fungicides containing chlorothalonil or copper sulfate if botrytis was problematic last year. Avoid overhead irrigation.

Fall Sanitation

Remove all spent foliage in fall. Add a 2-4 inch mulch layer over soil, leaving the crown exposed. This prevents fungal spores from splashing up onto plants.

Monitor and Reapply Fungicide

Check for new spots and retry fungicide if needed, especially during rainy springs. Catching diseases early is key.

Plant Resistant Varieties

Some modern and heirloom peonies have better natural disease resistance. The classics ‘Sarah Bernhardt’ and ‘Karl Rosenfeld’ are good choices.

With prompt treatment at first signs, black leaf spot diseases don’t have to ruin your peony displays. A bit of maintenance keeps your plants happy and flowering.

What if Black Spots Don’t Go Away?

If aggressive black spots persist despite your best efforts, the disease may have embedded itself in your peony’s crown and roots. At this point:

• Black spots spreading to lower leaves likely indicate phytophthora blight. Without stopping its root rot, the peony will die.

• Botrytis that won’t resolve often signifies the plant is weakened and vulnerable to repeat infections.

In either case, you have two options if fungal treatments fail:

1. Remove and destroy the peony.

2. Dig up the peony in fall and replant in fresh soil, pruning any rotten roots before replanting at proper depth. Give added space and care to help the recovering plant.

Though extreme, removing chronic diseased peonies prevents spread and allows for a fresh start.

How to Prevent Peony Black Leaf Spot

Stopping black spot diseases before they take hold is ideal. Here are tips to avoid problems:

• Allow ample space between plants and avoid crowding.

• Provide good drainage and amend soil to prevent puddling.

• Water at the soil line, not overhead.

• Clean up spent foliage and destroy (don’t compost) in fall.

• Apply mulch layer over soil to prevent fungal splashing.

• Monitor young shoots and treat immediately at first spots.

• Remove susceptible varieties and replace with resistant cultivars.

Keeping peonies healthy, happy, and spot-free enhances their stunning floral display. With prevention and early treatment, black leaf spots don’t have to threaten your spring blooms.

Alternative Causes of Black Spots on Peony Leaves

While fungal diseases are the most likely cause of black peony leaf spots, a couple other possibilities include:

Peony Measles

Also called peony leaf blotch, this bacterial disease causes small reddish spots on upper leaves in summer. Spots gradually enlarge to purplish-black. It spreads in humid, rainy weather. Fall cleanup, removing infected leaves, good air circulation, and monitoring helps control spread.

Physical Damage

Injury from hail, blowing debris, or mechanical damage can cause black bruising on peony leaves and shoots. There will be no associated wilting or dieback. Usually physical damage is isolated or scattered rather than impacting multiple leaves.

Chemical Burn

Herbicide drift or contact with certain pesticides can sometimes burn black spots on plant foliage. Damage will be random rather than symmetrical spots. Browning, yellowing, and curling of leaves may also occur.

By considering timing, pattern of spots, and other symptoms, you can deduce whether fungal disease, physical injury, or chemical exposure is the culprit behind black leaf spots on your peonies.

Don’t Let Black Spots Blight Your Peony’s Splendor

Peonies are the divas of the spring garden, lighting up borders and bouquets with their sumptuous blooms. But their floral extravagance fades fast when black leaf spots take hold. Stay vigilant for early symptoms and employ preventative care. With prompt treatment, though, you can contain these common fungal diseases and enjoy flawless peony flowers.