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Past Articles Library | Pests and Disease of Peonies

The easiest way of preventing the invasion of pests and plant diseases as far as peonies goes is prevention.  What does this really mean?  Well, you need to be diligent when it comes to cleaning up the area by which your peonies are located.  Remove spent blooms, and fallen leaves.  To keep the peony looking its best, cut away diseased and/or dead stems but before you make your first cut make sure that your pruners are sterilized.  This will prevent plant disease from moving from one plant to another.  How do you do this? The best approach is to soak your pruners in water and bleach solution. Take the time while the pruner is soaking to scrub it.  Once clean, rinse off with plain water and allow to dry in the sun.  Now you are ready to use your pruners but…to really keep the diseases and pests at bay, make sure to wipe down the cut surface every time you go to make a new cut.

As careful as you may be in your garden space, there will be times when pests and diseases appear.  Below are descriptions and solutions to pests and plant diseases that you will find in your peonies.

Botrytis Blight

If you have a problem with your peony, chances are it is this.  The blight is caused by rainy, damp weather.  Because of the timing of these environmental conditions, the part of the peony that is affected is the young shoots when they are less than 8 inches tall.  The wet weather causes the stems to rot at ground level or the stems become waterlogged.  Once this happens, the stems fall to the ground and become covered with a brown or black mass, which happens to be the fungus spores.  As the season progresses, the spores will grow into a gray mold, which will cover living stems, buds, and flowers.

This blight will eventually cause the buds to fall off and/or not open.  Flowers that open will be covered with the gray mold.

Since this is an environmental issue, there really is nothing that can be done but to reduce the effects one must be diligent about garden cleanliness.

Peony Blotch

This peony disease is also known as red spot or measles.  Why you may ask?  Well, it comes from the red spots that form on the leaves.  These spots are caused by a fungus that appears in the spring.  This fungus attacks all the above ground parts of the plant but it will not kill it in the short term.  Continued exposure to this fungus for several years can eventually cause the death of the peony.

As stated, this fungus will not kill the peony but the real harm of the disease is how it disfigures the plant.

There is no cure for this disease except keeping your garden clean.

Powdery Mildew

Have you ever walked out to the garden and found your peony covered in a light gray or white powder?  No you are not dreaming instead you have seen powdery mildew.  While this fungal disease normally does not cause the death of the plant, it does cause the flowers to be misshapen.

While there are chemicals that can be used to treat this issue, it is best to just let the situation work itself out.

Phytophthora Blight

This peony disease is caused by a fungus that lives in the soil called Phytophthora cactorum.  The signs of this disease can be seen at ground level where the stems emerge.  What bring this fungus to light are saturated soils and/or flooding.  The signs of this disease can be seen as leathery spots on the stems at ground level.  The stems that show this sign will eventually die.  As the disease spreads, it will reach the crown and cause crown rot.  This, in turn, will cause the death of the plant.

The only treatment for this disease is to remove the plant.

Southern Blight

This peony disease is also known as crown rot or white mold.  This is also a fungal disease that actually starts at the crown.  You may notice that the leaves in the crown area begin to turn brown.  As this happens, the stems begin to fall.  This is due to the fact that the stems are squishy and waterlogged, which prevents the stems from supporting themselves.

As the weather warms and the humidity rises, you will begin to notice little “white strings” going from the ground to the stems.  This will then turn into sclerotia, which looks like mustard seed that is white to red tan or brown.  As the sclerotia surrounds the stems the sclerotia will cause the soil to crust over and then the plant will die. 

There is no cure for this disease.

Foliar nematodes

As the name applies, these nematodes live on the foliage of the peony.  Once the damage starts, it progresses quickly.  It starts out as lesions between the veins of the leaves.  These lesions can be deceptive in appearance since they just look like waterlogged areas.  As the lesions grow, the damaged material will fall off, which will make the leaf look like it had been through a wind storm.  Other symptoms of this pest include stunted growth, and leaves with many colors. Also the plant produces no flowers and a rush of leaf growth at the crown.

Most of the time, older vegetation will show the symptoms described above but if there is a lot of rain this can change quickly.  Little droplet pools left on the leaves after a rain can create a “nematode highway” by which they can move from one part of the plant to another.

The only solution to this problem is to keep the vegetation as dry as possible.

Mealy Bugs

Mealy bugs are easily seen on peonies as white masses that cover leaves and stems.  While this pest normally will not kill the plant, large numbers can cause the plant to slow down its growth, drop leaves, and/or flowers. 

Another issue with mealy bugs is their production of honey dew, which is a sweet substance that ants love and black sooty mold grows on. 

To prevent this, keep your garden space clean and your peonies properly pruned.  This will create the strongest plants possible, which in turn can fight off the mealy bugs.  Also, invite beneficial insects to your garden space.  Finally, remove any overwintering sites for the mealy bug, which includes weeds, stacked wood and/or fallen bark.

While the pests and plant diseases of the peony are not that many, there is a key to preventing and/or keeping these issues under control.  What is this?  Well, it is to keep your garden as clean as possible.  If you do this you and your peonies will be happy for many years to come.


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Fungi Problems?

Mushrooms usually appear during the rainy months, but they can appear throughout the year.

If you have lots of mushrooms growing after regular watering, it could mean compacted soil is not allowing water to drain properly.

Allow the area to dry out, aerate it, and apply some gypsite to help make the soil more porous.

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