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Apple Tree Disease

Written by Dave Gs • February 08 Apple Tree Diseases

Apples are one of the best fruit-tree choices for gardeners in cooler areas. The give a good yield of the most versatile and the most popular fruit there is, and they thrive in cooler climate zones than most other fruits. They will also grow in a range of soils and garden conditions, but they can have some problems that may need taking care of if you want to get the best possible results. There are some diseases that can affect your trees, so being able to recognize them, and deal with them, is basic knowledge for anyone who wants to grow this popular crop.

There are a lot of apple diseases listed, but most of them are rare or do not do serious damage. Which disease is a significant problem can depend on where you live, but there are just a few that are serious enough to regularly cause problems for many gardeners.

Apple Scab

This disease is both wide-spread and serious because it can affect both foliage and fruit. This fungus disease spends the winter in dead leaves from infected trees. In spring spores are released that travel to the trees, causing olive-colored spots to develop on the underside of the leaves and on the young fruits. It spreads most rapidly during warm, rainy weather – April showers can bring more than just flowers. As the disease develops leaves can become badly spotted and thick scabs develop on fruit. As the drier weather of summer arrives the spread of this disease is reduced, but during a rainy summer it may continue. Often with the warm, rainy weather of early fall there will be a new spread of the disease.

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Apples that develop scabs early in the season will be deformed in shape, as the scabbed areas do not grow as rapidly as the healthy tissue. Scabs that develop later have little effect and since they are only on the skin they can be ignored, especially when cooking. They have no effect on the flesh or eating quality of the apple. Infected leaves will fall early and several seasons of bad infection can weaken the trees and reduce cropping.

There are three approaches to controlling this disease. First, look for varieties that are resistant to apple scab, especially if you live in an area where it is common. Secondly, remove all the fallen leaves beneath your tree in fall. If you shred and compost them, by spring they will be decomposed and cannot re-infect your trees. Thirdly, use a suitable fungicide early in the season, just after the petals fall from the blossoms. For organic growing, use sulfur as a protective coating on the leaves, applying it regularly if it is washed off by rain. Other chemicals provide surface protection, while some go inside the tree and prevent the disease spreading. If early control is used the disease cycle is broken and later infections will usually not occur – or at least only at the end of the season when they do little harm.


This is a bacterial disease that enters the tree during rainy weather in spring. It gets inside the tree through the blossoms and through the bark. Once in the tree if forms a damaged area on the bark, called a canker. This looks raised around the edges, but shrunken and dead in the center. During wet weather cankers ooze bacteria, which is then blown by the wind, or carried by insects, to other trees or to other parts of the same tree. The bacteria multiply beneath the bark, killing it and causing branches to then die. If you see the leaves on a branch suddenly wilt and turn brown, looking like it has been scorched, that is fireblight, and the appearance is why it has that name. This disease can also affect pears, quinces, hawthorns and firethorn bushes. Trees can die if this disease is not controlled.

If you have any sign of fireblight one year, before the next spring you should check your trees carefully and prune out any dead branches or those with cankers. Do this during cold weather, below 45 degrees, so that you don’t spread the disease around. Cut 8 to 12 inches below the canker, since the bacteria spread below the bark into healthy wood. If you have a lot of problems with this disease, agricultural streptomycin is available as a spray. Apply this during the blossoming season until the petals fall. Put the spray on at the end of the day so that it dries as slowly as possible – this makes it more effective. Watch for fireblight on ornamental shrubs in your garden and treat them in the same way, so that they do not act as a source of infection.

Bitter Rot

This disease is found mostly in southern states, since it needs warm weather to thrive. It causes soft patches to develop on the fruit, which spread and cause rotting and loss of the fruit. It develops during the hot weather of July and August and fruit quickly becomes soft and rotten, before drying out and turning into mummified apples that hang on the tree. There are no symptoms on the leaves. It spends the winter in the mummified apples and in cankers from other diseases or broken limbs. So to control this disease, remove all mummified fruit in winter and prune to remove dead wood, cankers and other damaged parts. Fungicides can also be applied if you live in an area where this disease is widespread – ask at your local garden center.

Other Apple Diseases

There are a number of other diseases that can occur from time to time on apple trees. They may cause leaf spots or mildew, or rotting of the roots and trunk. To reduce the likelihood of disease, make sure you plant in well-drained soil, with good air circulation around your trees and prune them correctly and at the right times of year. Although all these diseases can sound scary, do not be put off growing apple trees. The small amount of care and attention they require is more than repaid by the bountiful harvest of delicious fruit you will take from your trees.



Comments 10 comments

  1. June 27, 2017 by Lorraine Donner

    There is a photo above this article of apples with brown areas on them. My apples now look like that. I am new to growing an apple tree. Which disease is this and what do I do?

  2. This summer we had an unusually wet summer.Never seen anything like it !
    All of our mature apple trees have a fair # of apples but they are very small. I mean VERY small. Most have scab on them but so far I have been reluctant to spray anything. The apples in previous years were nice, especially our Empire apples.Also I see every year more what looks like lichen on the branches, so much so that the skin cracks and some of our Paula Red braches die.
    Can you explain? Last year we pruned as in the year before but never more than 25% But I admit I can grow hay and raise cattle but my knowledge of apple trees is limited.
    Thanks a lot!

    1. August 23, 2017 by David Goodfellow

      You need to thin your apples to get a good size. When they are the size of a quarter, remove them so you have just one apple every 6 inches apart. Scab is a common problem, but it is only on the surface. You will see the leaves fall early too because of it. If you can clean them all up – don’t compost them, burn them – you won’t get the early scab that distorts the fruit and keeps it small – just the later one that only leaves blemishes on the skin.
      If that really is lichen, its common on apples, especially in the country – it means you have good, clean air, and doesn’t hurt the trees. If you use a winter spray of dormant oil and sulfur, it will also clean moss and lichen off the trees, as well as helping control pests and diseases. Its accepted as an organic control, so don’t worry about harmful side effects.
      However, if the bark is splitting and branches dying, you could have Fire Blight, which is not good. The only control is to prune the branches about a foot further in than the dead bark shows – that is, into healthy wood.
      Hope this all helps, good luck with your trees.

  3. November 12, 2018 by Dave Dahlke

    My pears and apples are deformed. not round and do have rot spots on skin. None look like the pictures I have seen. I sprayed often in the spring.

    1. November 12, 2018 by G Dave

      Hard to be sure, but it sounds like apple scab. Do you have problems with spots on the leaves, which yellow and fall early? Scab in spring will cause spotting on fruit, that then doesn’t develop properly beneath the spot, causing deformed shapes. Are you spraying for fungus disease, and destroying all the leaves in fall? (Don’t compost them.)

  4. December 11, 2018 by Brenda Guy

    Does anyone know the name of an Apple that was dull red, hardly any sheen and always slanted. It was crisp and slightly tart. The most beautiful apple I’ve ever eaten. A disease killed off many orchards of this apple and growers quit them. This must have been in late 80s.
    I’m racking my brain trying to remember. Thanks

  5. May 4, 2019 by Dona Dalton

    I have a small golden delicious dwarf espalier tree with 6 beaches total. Noted with new growth and blossoms on two limbs on same side of tree are now wilted and the bark in the affected area looks shriveled as well. I cut off the wilted area about 6 inches. I note today it looks like it’s progressing up the branch. Is this fire blight? Doesn’t look burned just wilted and lifeless tip of branches. What can I do. I love this tree and the shape. It is in a lawn area. A very wet winter and spring in Northern California this year. Tree only 3 years old. Thank you Dona.

    1. May 5, 2019 by Dave G

      I am afraid that does sound like fire blight. The wet spring, and the shriveled bark both support that possibility. Is the damaged bark within 6 inches of the trunk? If so you will lose the tree, if not this year, then over a couple of years. If not, remove the branch 12 inches below the last trace of dying bark. Since it is spread by wind and rain from other diseased trees we always see more of this disease in wet springs. If it shows no more signs, be sure to only prune during dry periods, as the freshly-cut surfaces are easily infected. Good luck, I hope your tree makes it.

  6. June 2, 2019 by Daryl

    I am growing apple trees from seeds, they are about 3 yrs old now in large pots. I’m noticing an issue with them as one tree half the brand and trunk is brown. Limbs died off starting next to the main trunk.. can this be cured or do I need to destroy the tree..? they are all about 5-6 feet tall. I did have 13 but Im down to 7..

    Thank you

    1. June 3, 2019 by Dave G

      Sounds like fireblight – once it reaches the main trunk you can’t save them – sorry. I don’t want to be discouraging, but why grow from seed? You need hundreds if not thousands to find a tree superior to the varieties already available – including wonderful historical heirloom ones. I suggest you learn grafting instead – then you can use your seedlings for root-stocks!