Common Diseases of Crabapple Trees
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.
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: 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.
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.
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.
- 1 tbsp baking powder
- 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.
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?