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Problems

Peony Diseases Powdery Mildew Rabbits Slugs Spider Mites

Peony Diseases

What causes the flower buds on peonies to turn black and not open up?

Botrytis or peony blight is a fungus disease which effects the plants and will causes this to happen.

Does the disease cause any other symptoms?

Usually not, even though occasionally it causes young shoots to turn brown and fall over.

What is the best method of control?

Sanitation is the best way to go. Remove and destroy all infected plant parts as soon as they are noticed. In the late fall cut all the peony stalks off just below ground level and destroy them.

Is there a chemical which can be used?

No, not unless you have or can purchase Benomyl or Benlate which is labeled for controlling the blight on peonies.

Are the ants necessary on peony plants?

No, the ants are on the peony to collect the sugar solution available when the flower opens.

Powdery Mildew

What type of symptoms are caused by powdery mildew?

Just as the name says, the disease causes a white powdery substance on the leaves and flowers. It may also cause the leaves to be twisted and distorted.

Which flowers are affected?

Powdery mildew is common on roses, zinnias, begonias, phlox, monarda and numerous other plants.

How is powdery mildew controlled?

Funginex and Chlorothanonil (Daconil 2787 or Ortho Multi-purpose fungicide) are recommended fungicides for ornamental plants.

Rabbits

What can be done to keep the rabbits off the flowers?

There are several ways to control rabbit damage. Rabbit proofing your yard with fencing is the most effective. Care must be taken to ensure that they can't crawl under. Repellents can also be used but with limited effect.

What type of repellents are available?

There are commercial repellents which can be applied on the grass around the garden and directly on the flowers. Dried blood and moth balls will also work but need to be replaced every time it rains.

I've heard you mention a home remedy with red pepper and glue. What are the exact proportions to use?

Yes, this remedy is very popular. The recipe is made up of 2 tblsp ground red pepper, 1 tblsp Elmer's white glue and a quart of water. Tabasco Sauce can be used as a substitute for the pepper.

Slugs

What can be done to keep the slugs under control?

Since they are not an insect the normal chemicals such as malathion won't work on them. There are several baits available which work well. Bug-geta liquid snail and slug killer is commonly available and does a good job. It gives off an odor which attracts the slugs. They eat it and proceed to die.

Can they be controlled without using a chemical?

Yes, but it's very difficult. Beer, put out in a partial buried pie tin just before dark, works as a good natural bait for slugs.

Which plants do the slugs feed on?

They really don't seem to be too particular about what they eat, but are a serious problem on Hosta.

How do slugs overwinter?

They overwinter in the soil or under litter and debris. Cleaning up the garden in the fall will reduce the overwintering population.

Spider Mites

What type of damage do spider mites cause plants?

Spider mites are tiny plant pests which suck sap from plant leaves. They multiply rapidly and kill plants if not controlled.

Which plants can get infected with mites?

Almost any plant can have mites, but marigolds are commonly affected.

How can we tell when plants have mites?

Spider mite infestations can be detected by holding a piece of white paper under a suspect leaves. Tap the leaves lightly. If mites are present they'll fall onto the paper and appear as tiny crawling specks.

How can they be controlled?

Mites can be controlled by applying an insect such as malathion or by physically washing them from the plants with a strong spray of water. Treatment must be repeated weekly for at least 3 weeks.


Todd Weinmann, Extension Horticulturist & Master Gardener Coordinator
Phone: (701) 241-5707
E-mail: todd.weinmann@ndsu.edu

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