The cloud of red blossoms on a flowering crabapple brighten the spring garden. While the budding leaves and fruit are an added attraction to crabapple trees, the observant homeowner may note ugly spots developing on new leaves. Crabapples are prone to a fungal infection called apple scab. In severe infections, the fungus will affect the fruit, causing both leaves and fruit to drop off the tree. The best treatment for apple scab begins in the fall, as the tree prepares to go dormant for winter.
Select a variety of flowering crabapple that's resistant to the apple scab fungus. Red-flowering varieties, such as "Cardinal," "Prairifire," "Purple Prince" and "Royal Raindrops," are all rated as having excellent resistance to apple scab by J. Frank Schmidt & Son.
Apply a foliar spray of zinc sulfate and urea in the fall. This spray forces the tree to drop its leaves quickly and causes rapid decomposition of the leaf litter.
Rake and remove all dead leaves and dropped fruit immediately in the fall. The apple scab fungus overwinters in dead leaves. When the early spring rains arrive, the spores are released, infecting the young leaves and apples.
Prune the flowering crabapple in late winter or early spring, removing dead and broken branches, suckers and water sprouts. Thin the interior branches, removing crossed and crowded branches so the breeze moves freely through the tree. Apple scab fungus requires several hours of a moist environment in order to infect the tree. Good air circulation helps the branches and leaves dry quickly after a rain.
Spray with a fungicide when the tree's buds are barely green at the tips. Continue spraying the fungicide at two week intervals until the weather becomes warm and dry. Preventing the apple scab fungus from infecting the new leaves helps prevent it from infecting the fruit.
Monitor the tree for signs of apple scab fungus. Remove infected leaves and fruit from the tree immediately, place in a garbage bag and put in the trash. Don't put infected green matter in your compost pile.
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Things You Will Need
- Zinc sulfate and urea spray
- Garbage bags
- Anvil pruners
- Fungicide spray
- Vigilance is key to treating apple scab fungus on flowering crabapples.
- Resistance to the apple scab fungus doesn't guarantee that your tree won't become infected. Follow the spraying schedule and clean up all debris and plant matter around the tree.
- Wear gloves, long sleeves and pants, safety glasses and a dust mask when spraying and pruning your flowering crabapple tree.
- Keep all sprays and fungicides out of reach of children and pets.
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