Following on from my article on why your peonies might not be flowering, I thought I would talk about peony pests and diseases. Peonies are susceptible to bacterial and fungal diseases and a few garden pests which I start with below. I have covered the ones that I have found that cause the main problems and some ideas on what to do if an infestation of them occurs on your peonies.

Pests that attack peonies

Ants

Ants love peonies and you may see scores of them crawling over your well-tended flowers. Don’t worry – the ants are harmless to peonies. They’re attracted to the droplets of sugary liquid on the outside of the buds. They also like the ‘honeydew’ secretion of the scale insects which I also talk about next. We include ants here as many people do worry about them but they really don’t do much harm.

What to do about ants

Don’t worry about the ants – they soon move on. If you really must control the ants then I recommend just positioning a few ant stations around the plant. They usually do the trick.

Scale insects

You need to look closely at your peonies to see the scale insects. If your leaves are turning yellow and dropping, get a magnifying glass and examine the yellow leaves for white flecks of something. These insects can also reduce the growth of peonies.

Some types of scale insects produce a shiny, sticky secretion called honeydew which also attracts ants. You may notice this on your leaves before you see the insects that look like tiny shells.

How to control scale insects

Try organic pest management strategies first by pruning out the stems and shoots that are heavily infested. While you’re doing this, manually rub the insects off the stems that are only lightly affected. Use a toothbrush and brush fairly lightly so as not to damage the hoot or stem further.

Next try biological management by introducing the scale insects’ natural enemies – labybirds/ladybugs or small parasitic wasps.  Lastly, you may have to resort to chemical means to address the problem. Try spraying with a pesticide, the issue is, it’s not always effective as their shells seem to provide some protection for them.

Thrips

Thrips are very tiny brownish insects that are really hard to see. Their effect is to puncture your flower petals, leaves holes and other disfigurations as well as discolourations. Leaves may lose color and then wither away. If a whole mass of these tiny insects descend on your plant, the leaves start to look scorched and the blooms are destroyed.

How to control thrips

Organic methods to control thrips start as simply as knocking them off the plant with a fine and strong spray of cold water from your garden hose. Focus on the undersides of the affected leaves. Repeat this daily for three or so days to get all the thrips. Beneficial, to you and not to the thrips, insects to encourage include spiders and mites. Also use mulches such as aluminium that disorient the thrips.

Chemical solutions include insecticidal soaps or a systemic insecticide that can reach into the plant tissue. Thrips like to hang out there.

Diseases to watch out for on your peonies

Blights

This is a disease of which there are several varieties.

Bacterial blight

This causes spotting on the peony leaves. It’s sometimes accompanied by rings of dark red pigment or yellow haloes.

What to do

Remove and destroy the plant debris at the end of the season. Ensure there’s good air circulation in your plant and avoid watering it from above.

Botrytis blight / Peony wilt

This is a common fungal disease of peonies. It starts by affecting the young shoots in spring. They discolour then wilt and fall over. Later in the season, the buds may become brown. Affected leaves can develop clumps of fuzzy, grey fungal spores.

What to do

Remove the affected plant parts and be sure to destroy all debris at the end of the season. Apply a fungicide when you notice the problem. In addition, don’t water from overhead and be sure not to over-water; keep the plant’s humidity low.

Phyotphthora blight

You notice this when the infected plant parts before leathery and turn dark brown and black. Shoots may die off. The crown (base) of the plant may develop a dark and unpleasant wet rot.

What to do

Once plants are infected with this, there’s nothing to be done. Remove and destroy the infected plants. Ensure that you don’t plant any further peonies in wet spots in your garden.

Southern blight / Crown rot

The stems, at their base, become water soaked. You may also notice thick fungal mycelium that looks like a rope in texture. There could be hardened spheres of mycelium that turn from white to red as they mature.

What to do

There’s nothing for it but to destroy the affected plant. And don’t replant any peonies in that space.

Leaf blotch (aka measles)

This appears on the leaves and stems of peonies as small reddish splotches. These often merge together  to form large and irregularly shaped purple blotched.

What to do

Remove the affected plant parts and apply a fungicide to the rest of the plant. Don’t water the plant from above and don’t let the plant sit in water – keep the humidity low.

Root rot

Root rot occurs when the crown (base) of the plant and the root become wet and attracted disease. The plant becomes stunted in its growth. It turns yellow, wilts and dies.

What to do

Remove all the infected plant.

Powdery mildew

This is a common problem with peonies. The leaves, flowers and young stems  become coated with a white powder. The flowers may become mis-formed.

What to do

Apply a fungicide to all parts of the plant when you notice the problem. This disease is unsightly but not deadly.

Viruses

Viruses of various sorts can attack your peony plants. You may find light and dark green mottling on the stems and leaves, stunted growth, leaves that curl up and just poor health in general in your peony plant.

What to do

If the problem is just the mottled leaves and the rest of the plant seems to be OK, then just leave it alone. However, if the problem is more serious, such as stunted growth, there’s no hope for your plant and you need to remove it.

Nematodes

Root know nematodes are an infestation in which the feeder roots acquire small galls. This is a ball of root tissue that’s grown around one or several living parasites. It usually takes one or two growing seasons for these to develop fully enough to be of trouble.

Your peony plant becomes poorly and the stems remain thin. If you notice this, you need to dig down to the roots to see if these galls have developed.

What to do

You need to remove the infected roots and the soil around the plant. Tis may mean destroying the entire plant and taking away all the soil. It’s important to clean the area of the infestation. It’s best to grow another plant in that space for the next three years, one that’s not susceptible to nematodes.

Verticillium wilt

This results in the shoots of the plant wilting. In this case, there’s no root rot present or any damage to the crown of the plant.

What to do

Remove the infected plants and burn them. Don’t plant peonies in the same place in the future.

One problem I often have is peonies getting tall and them falling over, check out my guide on how to stop peonies falling over in my guide here.

To keep a close eye on your peonies’ health, consider growing peonies in pots. If you grow your plants in your garden, make sure to prepare them well for the winter.

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