The apple tree is a deciduous fruit tree that thrives in well-drained areas with full sun and good air circulation. Part of the rose family, the apple tree blooms in late spring, harvests in late fall and requires a period of dormancy to produce plentiful fruit the following season. Apple variations that thrive in Texan areas must have low chill requirements. Even when this requirement is met, however, Texas apple trees are susceptible to several diseases, some of which can injury the tree when left untreated.
Apple scab is a fungal disease that can cause severe damage and disfiguration to the apple tree. The fungal spores of disease are carried onto the apple tree by wind and rain. The disease infects the foliage, blooms and fruit of the tree. It requires moist, wet conditions. Infected foliage will become distorted and twisted. These leaves will develop black, circular spots that will cover both sides of the leaf. The foliage will begin to yellow and fall from the tree. Stems that are infected will cause early fruit drop. Infected fruit will develop greasy-looking, gray colored, sunken lesions with red halos. The potential for apple scab is greatly reduced with the removal of debris and dead leaves from under the apple tree. The disease is controlled with a fungicidal treatment that contains copper or sulfur.
Fire blight is a bacterial disease that lies dormant on cankers that exist on the tree. During moist, warm periods, the disease is transported onto the tree, infecting the twigs, branches, foliage and fruit. Infected areas of the apple tree ooze a watery, bacterial liquid that darkens when exposed to air. Infected flowers wilt, and infected apples turn brown. Twigs and branches experience die-back, which is combines wilting and stunted growth. These areas also develop cankerous areas that are initially inconspicuous. Infected foliage will turn black and severely infected fruit will mummify. Diseased areas must be pruned from the tree to give the tree a better chance of survival. The damaging effects of the disease can be controlled with copper-based fungicidal treatments but will not eliminate the disease.
Verticillium wilt is a soil-borne fungal disease that generally results in the death of the apple tree. This disease can survive for many years in the soil without a host. The infection attacks the apple tree through its root system, killing tissue and cells that are responsible for transporting water and nutrients throughout the tree. Infected apples trees experience stunted growth, die-back, slow growth, browning and yellowing of foliage, leaf scorch, and stunting and rotting of fruit. Symptoms of verticillium wilt are often similar to other fungal diseases and present a challenge when diagnosing. The diagnosis is confirmed by viewing the interior of cut limbs: They display dark, vascular streaks. There is no cure or treatment for verticillium wilt. Infected areas should be pruned from the tree and the apple tree should be kept vigorous to reduce the presence of symptoms. Severely infected trees must be removed and discarded.