In advanced cases, melanose can also cause wood rot in stressed or old trees. When not busy learning about homes and appliances she's sharing that knowledge. As the disease progresses, the tree will grow poorly and produce less. Leaves, fruit and sometimes branches have a black, moldy appearance. Photo credit: L. Navarro, Instituto Valenciano de Investigaciones Agrarias, Bugwood.org, http://idtools.org/id/citrus/diseases/factsheet.php?name=Tristeza#. If the fruit is infected, small black spots will form on the rind and the surrounding area will remain green longer. Phytophthora citrophthora, P. parasitica, and other Pytophthora spp. Leaves may drop prematurely. Infected trees may decline and eventually die. The whole fruit will eventually turn black and give off a sour, fermented odor. Affected oranges develop yellow, circular lesions or scabs on their rind. Leaves may drop prematurely. Fortunately, most of these diseases are nonlethal, especially if identified and treated early. Photo credit: Gerald Holmes, Valent USA Corporation, Bugwood.org. And the best way for a home gardener to diagnose the problem is by visual inspection. » Pseudocercospora fruit and leaf spot. Greasy spot – Greasy spot is fungal infection that causes dark, greasy-looking spots on leaves, leaf drop, and reduced tree vigor. As the disease progresses, in humid conditions, a white velvety growth can be observed on the rind and the fruit will give off a pungent, rancid odor. When you know the symptoms you can quickly diagnose and manage a particular disease. Sunken spots form on the rind. Infected leaves may be thicker and leathery compared to healthy leaves. Melanose is caused by a fungus that reproduces on the dead wood of older citrus trees. Sweet orange tree more than half girdled by a Phytophthora lesion at the base of the tree. Small, brown spots surrounded by a yellow halo form on the leaf surface. There are three distinct syndromes of the disease: quick decline, stem pitting, and seedling yellows. http://idtools.org/id/citrus/diseases/factsheet.php?name=Psorosis, http://www.ipm.ucdavis.edu/PMG/r107100100.html. This damage occurs as the result of twigs or leaves rubbing against young fruit. A unique education agency, the Texas A&M AgriLife Extension Service teaches Texans wherever they live, extending research-based knowledge to benefit their families and communities. Sunken spots form on the rind. Leaves may drop prematurely. A closer inspection will reveal typical rust fungal growths on the underside of the leaves. Fruits may have black specks. Wind Scar: This damage occurs as the result of twigs or leaves rubbing against young fruit. Citrus Whitefly. Infected fruit will change color prematurely and may drop early from the tree. Citrus canker is caused by a highly contagious bacterial pathogen. Brown Rot: The low-hanging fruit become infected first and then water will disseminate the fungus to fruit higher in the tree. Tan to gray, corky, wart-like scabs will form on the fruit rind. This can lead to yield loss and a general prolonged tree decline. Sooty mold does not harm the tree, but significantly covered leaves may lose some of their ability to photosynthesize. Leaf Yellowing: Magnesium, iron or zinc deficiencies and herbicide injury. Photo credit: Whitney Cranshaw, Bugwood.org, http://www.ipm.ucdavis.edu/PMG/r107303211.html. TheMelanose spots evolve to exude a red-brown gum, and become raised bumps that stand above the surface of the leaf. Physalospora rhodina). The rind will first turn brown near the stem end of the fruit and then will progress down the fruit forming brown, finger-like streaks. Oleocellosis: Peel oil is released when rind cells have been injured as a result of abrasion or rough handling. A gummy substance may also exude from the base of the trunk. A gummy substance may form around the bark lesions, impregnating the wood, eventually leading to the rapid decline of the tree. Fungal infection often occurs following a freeze or mechanical or chemical injury. As these spots darken, corresponding yellow spots will form on the upper leaf surface. Root rot – Both armillaria and phytophthora can cause citrus root rot. Feeder Root Rot: The fungus infects the cortex of feeder roots, giving the root system a stringy appearance. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74108.html. As the disease progresses, a gummy substance exudes from the spot, dries, hardens, and gives the leaf a sandpaper texture. This causes the affected area to remain green when the fruit matures, or turns yellow. The fungus infects the cortex of feeder roots, giving the root system a stringy appearance. However, when symptoms are produced, one can observe leaf yellowing, leaf deformation, twig deformation, stunting, overblooming, and premature fruit drop. Trees that have recently been transplanted often experience a difficult period of transplant shock, leading to a host of potential problems, including leaf wilt, leaf scorch, yellowing leaves, and leaf rolling or curling. Greasy spot disease is caused by a fungus. Gum pockets may form. Based in Houston, Texas, Meg Butler is a professional farmer, house flipper and landscaper. The leaves and fruit may also yellow, die and drop. As the disease progresses, a gummy substance exudes from the spot, dries, hardens, and gives the leaf a sandpaper texture. in history from New York University. Since the disease can be spread by as little as a gust of wind, orange trees are often felled and destroyed to prevent the spread of this disease. The dead bark frequently sloughs off the wood in vertical strips. Affected young branches die back from the tip, sometimes producing gum exudation. This disease remains dormant while the fruit is still attached to the tree. This fungal disease gets its name from the fact that the dark brown spots resemble tar. Severe Citrus Melanose infections result in the dieback of young shoots. Wood discoloration under the bark maybe observed. Leaves will exhibit yellow flecking, leaf cupping, and light green to yellow leaf veins. Infection of the trunk results in a dark, water-soaked areas, often with profuse exudation of a dark resin from the lesion. Melanose is caused by a fungus that reproduces on the dead wood of older citrus trees. When the bark is peeled back one can observe smooth depressions in the wood which correspond to projections extending from the inner bark.