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Cass County Extension

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 Insects, Diseases & Pests of Fruit Trees

Apple Maggot Control Apple Scab
Black Bugs on Ripe Fruit Fireblight
Frog Eye Leaf Spot Rabbit Damage
Suncald Prevention Vole Damage

Winter Protection of Trees

Apple Maggot Control

What type of damage do the maggots do to apples?

The apple maggot adult is a small fly which lays her eggs into the immature apples. The eggs hatch and the maggot tunnels around in the fruit leaving small brown trails. Even though the maggots have usually left the fruit before harvest, the apples are ruined.

Can the apple trees be sprayed to control the maggots?

Yes, a spray program can be initiated in late June and continued until early to mid August depending on the maturity date of the apple. Usually we recommend spraying the apples every 7-10 days with Sevin, Malathion, Diazinon or Methoxychlor. This would keep the adult insect from laying eggs into the fruit. Once the eggs are laid no control measures will work.

Is there a way of controlling the apple maggot flies without using chemicals?

Yes, the flies can be trapped by hanging red ball-shaped traps in the tree and coating them with tangle-trap or tangle foot. The balls should be about the size of croquet ball. The flies are attracted to the red color of the ball and when landing, will be stuck in place.

Are there any other things which can be done to reduce the number of maggots in the future?

Good sanitation is very important in reducing apple maggot infestations in the future. Pick up fallen apples as soon as they drop to prevent the maggots from burrowing out of the apple and into the soil.

Apple Scab

Is scab a serious problem on apples?

Usually it is not a big problem on apple or crabapple tress  but can be a serious problem on some of the flowering crabs such as Radiant which are quite susceptible. Apple scab is much more serious when we have cool wet weather in late spring or early summer.

What are the symptoms of apple scab?

Scab causes brown spots to develop on the leaves and may also cause them to pucker. As the disease develops the spots will turn black and leaves may fall. Scab may cause similar symptoms on the fruit.

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.

Black Bugs on Ripe Fruit

What is the hard shelled black insect which feed on ripe fruit?

This insect is called a sap or picnic beetle. They feed on ripe and over ripe fruits and vegetables, especially raspberries, strawberries and sweet corn.

Can anything be done to control these beetles?

Using an insecticide is very difficult because the sap beetles are not a problem until the fruit is ripe. General recommendations are to harvest fruit just before it is ripe and to remove and destroy overripe or rotting fruit.

Fireblight on Apples, Crabapples & Pears

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 tree 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 trees are infected?

Once a tree has been infected with fireblight we have only two choices. If the disease is serious and is progressing into large branches, the diseased branches need to be pruned out of the tree. If the disease has remained in small twigs and doesn't seem to be progressing, we can just watch the infected areas and remove the following spring. When pruning you must cut back 8-12" beyond the furthest advance of the disease.

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. Fireblight is very contagious and is easily spread. After using bleach be sure to wash your pruner or saw with water and then oil them.

Can anything be done to prevent Fireblight?

Apple and pear trees can be sprayed with an antibiotic such as Streptomycin when flowering and after a hail storm. 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 spraying do any good after the tree is infected?

No, the spray for fireblight acts as a preventative and won't stop the disease once it's in the plant.

Will fireblight kill trees?

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

Rabbit Damage

Can anything be done for trees which have been damaged by rabbits?

Once the damage has occurred,  it's pretty difficult to repair. Covering the eating wounds with pruning paint or latex house paint would seal the wounds and prevent further drying out of the tissue.

Will trees die from the rabbit damage?

When the bark in eaten off of the trunk or a branch, all parts of the plant beyond the eating will most likely die. If the bark is only eaten off on one side of the limb, the bark will regrow over a number of years. Applying a wound dressing is helpful in those situations because it will prevent further drying out of the damaged area.

What can individuals do in future years to prevent winter rabbit damage?

We recommend wrapping the trunks and branches of trees before winter. Putting chicken wire around trees will prevent rabbits from eating on them until the snow gets very deep.

Winter Protection of Fruit Trees

What kind of protection is needed to successfully overwinter fruit trees?

Two things must be concerned when preparing fruit trees for winter. Rabbits and voles like to chew on their bark and sunscald can damage the bark.

What are your recommendations for keeping the rabbits and voles away from fruit trees?

Your best bet would be to use some type of mechanical barrier. Using a good heavy tree wrap, can prevent damage. A cylinder made of fine mesh wire will also keep the rabbits away from the trunk. A gallon can or other metal around the trunk at the base will keep the voles away.

What is sunscald and how can we prevent it?

Sunscald is a damaging of the tree bark on the south or southwest side caused by the sun in late winter - early spring. The sun heats up the bark during the day and freezing temperature at night damage the cells. Using a tree wrap or some type of shading for the bark will prevent this damage from occurring.


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

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