Common Diseases of Crabapple Trees
Crabapple diseases can rob your trees of both beauty and fruit.
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 of trees, resulting in an attack of disease. This article will help you identify what disease might be afflicting your tree, and how to treat it, and prevent it in the future.
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, .
Crabapple disease #2 - Fire blight
Symptom: Shriveled, 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 either doesn't develop or 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.
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 the horns develop.
Crabapple disease #4 - Powdery mildew
Symptom: A white substance on leaves
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. If taller trees are near the crabapple, trim them so that they don't shade the crabapple too much. Plant crabapple trees on a south, east or west exposure for maximum sunlight. Prune the tree to allow for adequate air flow through the canopy.
Recipe for powdery mildew spray
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.
- 1 tbsp baking soda
- 1/2 tsp dish soap
- 1 gallon water
- Backpack sprayer
- 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.
Pink or white? Which Crabapples are more resistant to disease?
There really is a difference in disease resistance between pink and white crabapples. In general, pink-flowered crabapples are more susceptible to diseases then white-flowering crabapples. In my own garden, my pink "Profusion" tree in the front yard is plagued by apple scab, and sometimes powdery mildew, if we have a wet spring. In a really bad year, it can be completely denuded of leaves by August. In contrast, my white-flowering "Golden Raindrops" out back never has problems with any disease...ever! If you are planning to buy a crabapple tree for your yard, consider getting a white tree for their hardiness. I highly recommend "Golden Raindrops". In full bloom it is billowy white. The bees and butterflies LOVE it! In fall, it's oak-shaped leaves turn brilliant yellow with red on the edges. The fruit is bright, golden-yellow to red, and are enjoyed by many of the songbirds that inhabit our yard.
"Golden Raindrops" crabapple.
Resource list of information on crabapple diseases
Still need more information? Find out what you need to know at these informative websites.
- Apple Scab
Management guidelines from the University of California's Agriculture and Natural Resources webstie
- Fire Blight
Information about Fire Blight from the Colorado State University Extension Service
- Deciduous Tree Diseases
Comprehensive website by North Dakota State University on pests and diseases of our native trees.
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?