Apple Scab on Flowering Crabapples

What causes brown spots to develop on the leaves and the leaves to fall off?

During periods of frequent rainfall and high humidity the leaves are infected with a fungal disease called apple scab which may also cause the leaves to pucker. The spots will eventually turn black and the leaves may fall. It may cause similar symptoms on the fruit.

Is apple scab a serious problem?

Yes, especially on some of the flowering crabs such as Radiant which are quite susceptible. It is much more serious when we have cool wet weather in late spring or early summer.

Can anything be done now to stop the leaf drop?

No, once the leaves are infected with apple scab or frog eye leaf spot spraying would do no good. Cleaning up and disposing of the fallen leaves will cut down the chances of re-infection next year.

Will the loss of leaves damage the trees?

Losing leaves is never good for a tree, but at this time of the year it won't cause any permanent damage. The trees should leaf out normally next spring.

What treatments will help control the disease?

When weather conditions are right for the disease, trees can be sprayed with a fungicide such as Captan or a combination of Benomyl and Captan. If your trees have shown extreme susceptibility in the past you may want to spray with a fungicide every 10-14 days during wet weather.

Is Frog Eye leaf spot similar to apple scab?

Yes, the symptoms and controls are very similar. This makes control easier because absolute positive identification isn't necessary.

Ash Antracnose

What is causing the ash trees to drop their leaves?

When the young leaves are infected by a fungus called anthracnose, they will fall off. If you look at the fallen leaves you can see brown spots or black blotches on them.

Is there anything which can be done to stop the disease?

Anthracnose can be prevented by using a fungicide, but once the leaves are infected spraying won't do any good. Fungicides are effective in preventing disease infection but will not stop the disease once it has infected the leaves.

What will happen to trees which lose their leaves?

They will leaf out again within a few weeks. Watering the tree if conditions are dry and fertilizing would help.

Is this an unusual situation?

No, actually it's pretty common. Cool, moist, humid conditions are very conducive to anthracnose disease.

Dutch Elm Disease

What are the normal symptoms of Dutch Elm disease?

In most cases you will see a yellowing of leaves in a portion of the tree. This yellowing will gradually spread over the entire tree killing it within a year or two.

How can a person know if there elm tree has Dutch Elm disease?

The only way to be absolutely sure is to have a sample tested at a diagnostic lab. To check for yourself, prune off a branch with yellow leaves and remove the bark. If the branch is diseased you'll see brown streaks running lengthwise in the sap wood.

What can be done to prevent the spread of disease?

Sanitation is the best method of controlling Dutch Elm disease. Diseased trees should be detected, removed and the wood destroyed or debarked. Dead and dying elm branches or trees, whether diseased or not, should be removed. They are breeding sites for the bark beetles.

Are any chemicals available for controlling Dutch Elm disease?

Yes, but they are expensive and must be repeated every 3 years.

Will all the elm trees eventually die from Dutch Elm disease?

That's a very difficult question to answer. A cure could be found and better methods of prevention may be developed. For the time being our best bet is good tree care and sanitation. 

In the spring is it necessary to get rid of the elm wood in your firewood pile?

Yes, if the bark is on the wood. The bark beetle which spreads dutch elm disease overwinters and reproduces in elm fire wood which has the bark attached.

How can a person find out if any of their firewood is elm?

Check with your city forester. I'm sure that they have someone who would be happy to check your firewood pile for elm wood.

Fireblight on Cotoneaster

What type of damage is caused by fireblight?

The first sign of a fireblight infection is the rapid browning of leaves especially on the tips of branches. The brown leaves will hang on the shrub and the stem tips will bend over. The infected twigs, stems and branches will turn almost black in color.

Which plants are infected by fireblight?

Luckily, the only plants which get fireblight are those related to the apple. This includes apples, pears, flowering crabs, mountain ash and cotoneaster.

What can be done once the shrubs are infected?

If the disease is spreading rapidly it may be necessary to prune out the diseased areas. You must cut back 8-12" beyond the furthest advance of the disease. Use a 10% bleach- 90% water mixture to sterilize your pruner or saw between cuts. Fireblight is very contagious and is easily spread.

Will fireblight kill the shrubs?

Yes, it can kill shrubs if they are susceptible and we don't prune the disease out as it gets into larger branches.

Fireblight on Flowering Crabs & Mountain-ash

What causes a rapid browning of the leaves especially on the tips of branches. The brown leaves will hang on the tree and the stem tips will bend over?

A bacterial disease called fireblight which will also cause the infected twigs, stems and branches tol turn almost black in color.

Which plants are infected by fireblight?

Luckily, the only plants which get fireblight are those related to the apple. This includes pears, flowering crabapples, mountain ash and cotoneaster.

What can be done once the trees are infected?

Once a tree has been infected with fireblight we have only two choices. If the disease is spreading rapidly it may be necessary to prune out the diseased areas. You must cut back 8-12" beyond the furthest advance of the disease. Fireblight is very contagious and is easily spread. If the disease has remained in small twigs and doesn't seem to be progressing, we can just watch the infected areas.

Is there any precautions we should take when pruning?

Yes, we need to dip the pruner or saw in a mixture of 10% bleach and 90% water between each cut to prevent spreading the disease when pruning. After using bleach be sure to wash your pruners or saws with water and oil.

Is there any chemical labeled for spraying trees?

No, the spray for fireblight is only for use on apples and pears.

What can be done to prevent fireblight infection?

Painting pruning wounds will help prevent fireblight from getting in. Over fertilize with nitrogen fertilizer and excessively pruning also increases the chances of fireblight infection.

Will fireblight kill the trees?

Yes, it can kill trees if they are susceptible and we don't prune the disease out as it gets into larger branches.

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 plants are affected?

Powdery mildew is common on lilacs, alpine currants, and numerous other plants.

How is powdery mildew controlled?

Pruning of alpine currant and other ornamental plants may help but a fungicide is usually needed. Funginex and Chlorothanonil are two recommended fungicides for ornamental plants.

This page was last updated August 2002

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