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Common Diseases of Crabapple Trees

Updated on April 3, 2015
Diane Cass profile image

Diane is a lover of all things beautiful; music, art, antiques and nature. Her guides bring insight to topics she cares passionately about.

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Crabapple Diseases - Does Your Tree Have One?

Modern varieties of crabapple trees have been bred to be less susceptible, or even resistant to the diseases that plague them. Many factors can contribute to stressful conditions that can vex even the hardiest trees, resulting in an attack of disease. This article will help you identify what disease might be affecting your tree, and how to treat it, and prevent it in the future.

Apple Scab

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CRABAPPLE DISEASE #1 - Apple Scab

SYMPTOM: Dark Blotchy Spots & Yellow Leaves Dropping Prematurely

Apple scab is a fungus. It affects the look of a tree by marring the leaves with dark, blotchy spots. As it spreads, the leaves turn yellow and will drop prematurely. In a bad year, or if it happens to a tree with low resistance, it can nearly denude the tree by the end of summer. It can prevent the set of fruit in spring and cause unsightly scabs on any fruit that develop.

Cause: A wet spring will spread the spores from leaf litter on the ground. A secondary infection later will cause leaves to discolor and drop prematurely.

Organic Treatment: Spray tree with an anti-fungal agent, such as sulfur, lime and sulfur, or copper and sulfur products on a dry day between rainy periods in spring. Spray again in summer if leaf spots and dropping is noticed.

Prevention: Clean up and burn leaf litter in the fall. Keep tree pruned to allow air to flow through the canopy. This will help leaves to dry faster after rain, to keep the spread of the fungus to a minimum. Feed an affected tree a little extra fertilizer to make up for the loss of leaves, .

Fire Blight

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CRABAPPLE DISEASE #2 - Fire Blight

SYMPTOM: Shrivled, Blackened Leaves

Fire Blight is a bacterial disease. A tree with fire blight can develop blackened leaves that look like they have been burned. Patches can develop on branches and trunks that look either sunken, discolored or rough. Fruit doesn't develop and looks mummified.Twigs usually take on a blackened shepherd's crook appearance.

Cause: Insects, wet conditions, dirty pruning tools

Treatment: There is no cure for the disease

Prevention: The best way to discourage fire blight is to plant trees that are resistant to the disease. Other than that, practice good hygiene with your pruning tools.. Clean tools with a diluted solution of 10% bleach after every use. Keeping trees properly pruned also discourages wet conditions, by helping air flow through the canopy.

Clean Pruning Tools

The best defense against fire blight is to plant trees that are resistant to the bacteria, and to keep your pruning tools clean.

Rust

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CRABAPPLE DISEASE #3 - Rust

SYMPTOM: Powdery Spots on Undersides of Leaves

Rust is a fungal disease that attacks the leaves of a crabapple tree. The orange to black powdery spots form on the undersides of leaves. The leaves will yellow and fall off prematurely.

Cause: Junipers serve as host plants for the fungus where it grows as a gall on the branches. Wet conditions, usually in spring, cause the galls to form horns containing the fungus. They burst open and spread the fungus to other plants.

Treatment:Spray tree with an organic fungicide, as mentioned above for scab.

Prevention: Plant crabapple varieties that are resistant to rust. Don't plant junipers near your crabapple trees. If you do have junipers and crabapples in the same yard, police the junipers in the spring, removing any galls that form before they form horns.

Powdery Mildew

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CRABAPPLE DISEASE #4 - Powdery Mildew

SYMPTOM: White Substance on Leaves that Look Like Flour or Powder

Powdery Mildew is a fungal disease that affects the leaves by giving them the appearance of having been dusted with flour or powder. It can also distort the growth of the plant, making branches appear twisted, so it's not just a topical problem.

Cause: Crabapple tree is receiving inadequate amounts of sun and leaves aren't drying off properly after rain.

Treatment: Powdery mildew can be treated with a homemade solution made of water and baking soda (recipe below)

Prevention: Plant crabapples resistant to powdery mildew. Trim taller trees so that they don't shade the crabapple too much. Plant crabapple trees on a south, east or west exposure...never a northern one. Prune tree to allow for adequate air flow through the canopy.

This simple homemade solution can be used to control powdery mildew on all kinds of plants, not just crabapples. It is organic and easy to use.

Ingredients

  • 1 tbsp baking powder
  • 1/2 tsp dish soap
  • 1 gallon water
  • Backpack sprayer

Instructions

  1. Mix the baking powder and water in the sprayer container. Give it a good shake to mix it well. Add the dish soap. Cover and shake until blended. Use the sprayer, according to manufacturers instructions to spray the crabapple tree. Spray on a day that is clear and dry for maximum affect.
Cast your vote for Baking Soda Spray for Powdery Mildew Control

Resource List of Information on Crabapple Diseases

Still need more information? Find out what you need to know at these informative websites.

You may know of powdery mildew because you battle it on your roses every year. Did you know that most diseases that affect roses can affect crabapples as well? Have you heard of these other diseases?

Have You Heard of These Disease?

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    • jptanabe profile image

      Jennifer P Tanabe 3 years ago from Red Hook, NY

      My neighbor has a crabapple tree - now I'll know what's wrong with it if it gets sick!

    • SusannaDuffy profile image

      Susanna Duffy 3 years ago from Melbourne Australia

      I had a crabapple tree once but it died. Now I see it was rust, wish I'd read your article earlier!

    • evelynsaenz1 profile image

      Evelyn Saenz 5 years ago from Royalton

      Squid Angel Blesses!

    • evelynsaenz1 profile image

      Evelyn Saenz 5 years ago from Royalton

      I just discovered that I have a crab apple tree in front of my house. Thank you so much for writing about all the possible diseases that can effect crab apple trees. Now I will know what to look for if my crab apple tree seems sick.

    • Diane Cass profile image
      Author

      Diane Cass 6 years ago from New York

      @Frischy: Yes. Diseases that affect apple trees can also attack pear trees.

    • Virginia Allain profile image

      Virginia Allain 6 years ago from Central Florida

      Really scary to see all the things that can attack a tree.

    • Frischy profile image

      Frischy 6 years ago from Kentucky, USA

      This is an interesting and helpful lens. I don't have a crabapple tree, but I wonder if these diseases apply to other trees such as Bradford Pear.

    • Showpup LM profile image

      Showpup LM 6 years ago

      Most of these I hadn't heard of. Very helpful lens. Love the description and the photos.