Click on photos to enlarge Aboveground dieback. Characterization of Alternaria isolates associated with Alternaria Rot of Citrus PDF file, 1.7MB (2002 report to the Arizona Citrus Research Council) Yuma County Farm Notes University of Arizona: Irrigating Citrus Trees Writer Bio Renee Miller began writing professionally in 2008, contributing to websites and the "Community Press" newspaper. Citrus trees are nothing more than a large bushes and ought to be kept that way, as opposed to being trimmed to look like its tall-trunked shade tree cousins. This provides less … Citrus canker – A highly contagious bacterial infection, citrus canker causes yellow halo-like lesions on fruit, leaves and twigs of citrus trees. Diseases in Orange Trees. If allowed to progress unchecked, this lemon tree problem will eventually result in dieback, fruit drop, and leaf loss. Because of Arizona's extreme heat, citrus trees don't flush with new leaves as often as they do in more temperate, humid climates. Furthermore, citrus trees can produce fruit in all but the most shaded part of the tree, and need not be regularly pruned to allow light into the interior of the canopy. When you know the symptoms you can quickly diagnose and manage a particular disease. Diseases of Citrus in Arizona (2011) PDF version 1045 kb. Sleuthing out the root cause of your citrus tree's problem can be a fun activity and it's a great way to get to know your tree … Armillaria root rot Identification tip: Pale and wilted foliage, few leaves, and limb dieback are symptoms of Armillaria root rot, dry root rot, Dothiorella gummosis, and Phytophthora root rot.Look for cankers and oozing gum, cut under bark to inspect cambium and wood, and examine roots to help diagnose the cause. Greasy spot is a fungus, known as Mycosphaerella citri, that affects the leaves of citrus trees and thrives in tropical and subtropical climates. What one may think is a matter of aesthetics can actually be a matter of life or death to the tree. There are several common diseases that can impact citrus trees and that are caused by fungi, bacteria, or pests. Citrus Tree Diseases. And the best way for a home gardener to diagnose the problem is by visual inspection. Keep a close eye on your trees and look for the characteristic signs that you have sick orange trees. The fungus appears as yellow, dark brown, or black lesions that initially occur on the underside of mature citrus leaves. When trimming citrus trees, the most important thing is not trimming too much. Citrus tree leaves are susceptible to a host of diseases, fungi and pests. Greasy Spot. Below are some of the most common diseases of lemon with tips for treating them.