Although their fruit leaves a bitter taste in the mouth, flowering crab apple trees provide beauty and interest in a variety of landscape designs. The trees produce fragrant white and pink blossoms in the spring, often showering the lawn with a carpet of petals when the wind blows. Like many other types of fruit trees, crab apple trees experience their fair share of blights and diseases. The correct treatment for a diseased crab apple tree depends on the underlying disorder.
Correct soil deficiencies by taking a soil test near the roots of your crab apple tree. Adverse soil conditions can create unhealthy environments for apple trees, making them susceptible to pests and diseases. Correct any deficiencies that your soil tests reveal with fertilizers or soil amendments.
Look closely at the new leaves on your crab apple tree. Notice any areas that appear dull and smoky. Look for dusty, velvety sections of leaves. These early signs signal the presence of mildew and mold spores. Apple scab is one type of fungal disease that damages large numbers of crab apple trees. Check for wilting leaves that turn brownish-black, indicating the presence of fireblight. Watch for this at the time your apple tree begins producing blossoms and immediately after flowers fall from the tree. Treat these diseases by pruning away the affected areas. Use sharp pruning shears or a clipper saw to remove diseased twigs, leaves and branches. Place your cuts deep enough into the healthy areas to ensure the complete removal of the infected sections.
Spray your crab apple tree early in the season with a fungicide. Select a product intended for use on fruit trees. Look for one that contains chlorothalonil or propiconazole. Apply the fungicide according to the manufacturer's instructions.
Apply a pesticide to your crab apple tree if you notice a bug or worm infestation. Look for signs of bugs inhabiting your tree, such as small holes in leaves and barks. Use a magnifying glass to examine leaves and twigs. Some small pests leave behind fine webs and small black or white spots on the undersides of leaves. If you do not know which type of pests live in your tree, apply a broad-spectrum pesticide. Select a product formulated for use on apple trees and apply it according to the instructions.
Remove fallen leaves from the area under your crab apple tree in the fall. Rake these away before the snow falls in winter. These leaves often harbor mold spores, which lie dormant in the winter and attack crab apple trees in the spring.