The apple tree is a flowering fruit tree that prefers the warm and varying climates of the Northern Hemisphere. Susceptible to its growing location, these deciduous trees are prone to disease that can affect the tree and fruit. If your apple tree is infected, check with a horticulturalist or home improvement store for recommended chemicals that work best on different diseases in your geographic area.
Black rot is a fungal disease that spreads through the distribution of spores during rainfall. The spores develop and infect the tree during late winter and begin to show its affects on the tree during the spring. Black rot causes the tree's fruit to rot, its leaves to spot and its limbs to canker. An infected apple tree can show one or more of these symptoms simultaneously. Once the tree shows signs of black rot, fungicide and other chemical treatments will not help.
Remove all infected fruit and branches from the tree. Prune out cankerous sections of the tree at least eight inches around the infected area. Remove and then destroy or burn all debris from the tree because it can re-infect the tree and surrounding trees if not discarded immediately. Treat your tree with a chemical fungicide the following spring.
Fire blight is a bacterial disease that infects the tree during the winter, while the tree lies dormant. In spring, the tree will begin to show early signs of infection. It will ooze a watery, light-colored bacterium that runs from the branches, twigs and trunk cankers near the infection. As the ooze ages, it leaves dark streaks on the tree. Fire blight usually infects the flowers of the apple tree first, wilting them and turning them brown. If untreated, the infection will pass through the flowers, into the twigs and branches, and further into the trunk.
The spread of fire blight is highly determined by warm weather resting between 75 and 85 degree Farenheit with intermittent rain. Do not fertilize your apple tree, avoid heavy pruning and reduce, if not eliminate, irrigation during the blooming period. These steps will hinder the growth of the bacteria. Remove any wilted or browning flowers and blooms, and prune out any infected wood.
Powdery mildew is a fungal disease that attacks the flowering buds and shoots of the apple tree. The disease initially causes the underside of the leaf to yellow while spots begin to appear on the top. The top side of the leaf develops a white, powdery mildew and begins to crinkle, curl and roll up from the edges. Infected shoots will appear stunted and shriveled. Seriously infected trees will shoot their leaves prematurely, and shoots will die almost immediately. Infected fruit will be small and russeted.
Powdery mildew occurs when humidity is greater than 90 percent with temperatures between 66 and 72 degrees Farenheit. Fungicide sprays are required to control this disease; pruning very seldom helps.