Crabapple trees (Malus spp.) are favorites among those who enjoy trees with showy displays of pink or white blossoms and the occasional spoonful of crabapple jam or jelly. Once a crabapple tree begins to blossom, it will continue to do so for 1 to 2 weeks, and fruit size varies depending on variety. Crabapple trees grow best in U.S. Department of Agriculture hardiness zones 4 through 8, but like any other fruit tree, they are prone to diseases, pests and deficiencies, problems that can be solved naturally.
The most common fungal diseases in crabapple trees include apple scab (Venturia inaequalis), rust and powdery mildew. Apple scab results in leaf blotches, leaf yellowing and leaf drop. Rust appears as orange-red powder on the underside of leaves, whereas powdery mildew appears as white powdery talc on the tops of leaves. Fungal diseases respond to a number of different natural substances. Applications of compost tea, rock dust milk, soured milk, garlic oil, hydrogen peroxide, liquid kelp and liquid sulfur can be effective (see reference 4, p. 76). Compost tea is made by putting compost in a burlap bag or old pillowcase and allowing it to steep at least three days in a five gallon bucket. If using hydrogen peroxide, mix 8 ounces with a gallon of water (see reference 4, p. 121). To make rock dust milk, gradually add water to a cup of rock dust and stir until dissolved. Then add mixture to a gallon of water and strain (see reference 4, p. 123). A mixture of 5 tablespoons of baking soda, 2 cups of soured milk and 1 gallon of water makes for another potent anti-fungal spray (see reference 4, p. 112).
Although not as common as fungal disease, a bacterial disease called fireblight can infect the crabapple tree. The disease produces water-soaked spots that later become dry, dark and sunken with occasional cracks. The terminal ends of the twigs and branches appear burned or rusty. Branches may also form a “shepherd’s crook.” Besides pruning infected branches, spraying infected areas aggressively with compost tea and liquid kelp can effectively combat the disease by promoting beneficial bacterial growth. (Reference 4, p. 119)
Aphids, spider mites, borers and Japanese beetles are pests that pose problems for the crabapple tree. Aphids and spider mites can usually be washed off the leaves using biodegradable soap and water. For severe aphid infestations, add a tablespoon of hot pepper sauce to the mixture. For severe spider mite infestations, add diatomaceous earth to the mixture along with the hot pepper sauce. Borers can be stopped by stuffing tobacco into the holes that they have bored (see reference 4, pp. 118-119). The borers can also be handpicked. Traps, diatomaceous earth, citronella oil and garlic spray can be used to control the Japanese beetle. Biological controls are also helpful. Lady beetles and aphid lions control aphids; beneficial nematodes and Bacterium Thuringiensis are useful against Japanese beetles (see reference 4, p. 69).
One of the most visible signs of nutrient deficiencies is chlorosis, or a yellowing of the leaves. Because determining exactly which mineral a tree may be deficient in can be difficult for the typical gardener, a generally helpful way to deal with deficiencies is to apply rock dust. Rock dust us generally high in iron, calcium, sulfur, magnesium and more than 100 other trace minerals. Due to its high alkalinity, however, you may need to combine it with compost or peat moss. Be careful of the source, as some rock dust is combined with industrial byproduct chemicals. Spread four coffee cans full of rock dust evenly under the tree starting 2 feet from the trunk and extending 10 feet past the edge of the tree’s canopy. (Reference 4, p. 140)
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