Black band disease is a coral disease in which corals develop a black band. It is characterized by complete tissue degradation due to a pathogenic microbial consortium. The mat is present between apparently healthy coral tissue and freshly exposed coral skeleton.

White band disease (Acroporid white syndrome) is a coral disease that affects acroporid corals and is distinguishable by the white band of dead coral tissue that it forms. The disease completely destroys the coral tissue of Caribbean acroporid corals, specifically elkhorn coral ("Acropora palmata") and staghorn coral ("A. cervicornis"). The disease exhibits a pronounced division between the remaining coral tissue and the exposed coral skeleton. These symptoms are similar to white plague, except that white band disease is only found on acroporid corals, and white plague has not been found on any acroporid corals. It is part of a class of similar disease known as "white syndromes", many of which may be linked to species of "Vibrio" bacteria. While the pathogen for this disease has not been identified, "Vibrio carchariae" may be one of its factors. The degradation of coral tissue usually begins at the base of the coral, working its way up to the branch tips, but it can begin in the middle of a branch.

Black band disease was first observed on reefs in Belize in 1973 by A. Antonius, who described the pathogen he found infecting corals as "Oscillatoria membranacea", one of the cyanobacteria. The band color may be blackish brown to red depending on the vertical position of a cyanobacterial population associated with the band. The vertical position is based on a light intensity-dependent photic response of the cyanobacterial filaments, and the color (due to the cyanobacterial pigment phycoerythrin) is dependent on the thickness of the band. The band is approximately thick and ranges in width from to White specks may be present on surface, at times forming dense white patches. The pathogenic microbial mat moves across coral colonies at rates from to a day. Tissue death is caused by exposure to an hypoxic, sulfide-rich microenvironment associated with the base of the band.

Yellow-band disease (similar to Yellow Blotch disease) is a coral disease that attacks colonies of coral at a time when coral is already under stress from pollution, overfishing, and climate change. It is characterized by large blotches or patches of bleached, yellowed tissue on Caribbean scleractinian corals.

Yellow-band disease is a bacterial infection that spreads over coral, causing the discolored bands of pale-yellow or white lesions along the surface of an infected coral colony. The lesions are the locations where the bacteria have killed the coral’s symbiotic photosynthetic algae, called zooxanthellae which are a major energy source for the coral. This cellular damage and the loss of its major energy source cause the coral to starve, and usually cause coral death. There is evidence that climate change could be worsening the disease.

Coral diseases, comprising the diseases that affect corals, injure the living tissues and often result in the death of part or the whole of the colony. These diseases have been occurring more frequently in the twenty-first century as conditions become more stressful for many shallow-water corals. The pathogens causing the diseases include bacteria, fungi and protozoa, but it is not always possible to identify the pathogen involved.

Black pod disease is caused by many different "Phytophthora spp." pathogens all expressing the same symptoms in cocoa trees ("Theobroma cacao"). This pathogen if left untreated can destroy all yields; annually the pathogen can cause a yield loss of up to 1/3 and up to 10% of total trees can be lost completely. With the value of the cocoa industry throughout the world being so large there are much research and control efforts that go into these "Phytophthora spp." pathogens.

This pathogen can be located anywhere on the cocoa trees but is most noted for the black mummified look it will give to the fruit of the cocoa tree. Staying ahead of the pathogen is the best means of control, the pathogen can be greatly reduced if leaf litter is not allowed to stay on the ground and if the pathogen gets out of hand chemical control can be used. This pathogen is mostly found in tropical areas where the cocoa trees are located and need rainfall in order to spread its spores.

Adult walnut twig beetles carry spores of the "Geosmithia morbida" fungus, which grows profusely around the pupal chamber of the beetles. Following emergence from trees the beetles subsequently tunnel into branches and trunks of walnut for production of egg galleries or overwintering shelters. The fungus is introduced into the tree during this wounding where it subsequently germinates and grows.

The fungal mycelium initially colonize tissue immediately surrounding the beetle galleries. However, in less than a month black, oval-shaped, inky cankers extend considerably beyond the galleries and may reach more than 3 cm in length in susceptible hosts (e.g., black walnut). In the beginning these cankers develop in phloem and tissues formed by the cork cambium. The affected area is very shallow and never show the ‘open-faced’, perennial, target-shape typical of many canker diseases of trees (e.g., Nectria canker). Instead in TCD the bark remains firmly attached to the canker face making the necrotic areas very difficult to observe. Branch cankers usually are not visible until the outer bark is shaved to expose the beetle tunnels, although during late stages of the disease a dark amber stain may form on the bark surface in association with the cankers.

Each time a beetle tunnels into a tree a canker is initiated. Cankers also may continue to expand and penetrate into the cambium of the tree. Each such injury destroys the phloem and robs the tree of its ability to store and move nutrients. As TCD progresses cankers coalesce to further girdle branches greatly restricting nutrient movement. As the tree declines, more bark beetles are attracted and more cankers are formed.

Eventually the enormous number of beetle attacks and subsequent canker formation overwhelms and kills the tree. Thousand cankers is a progressive disease and its effects result from the culmination of a large number of relatively small cankers over a period of time. Just as a thousand cuts was once used as a form of human execution in Imperial China, black walnuts are subjected to death by thousands of branch and trunk cankers produced by infection from the "Geosmithia" fungus.

In end stages of the disease external symptoms become visible. Leaf yellowing on the exterior of the crown is often the first symptom and may originally be restricted to a single branch. However, as the cumulative effects of the girdling progress increasingly large areas of the tree are affected. Sudden leaf wilting, ultimately involving large limbs, characterizes end stage thousand cankers disease. In susceptible hosts, trees are almost always killed within 2–3 years after external symptoms of leaf yellowing are first observed.

The progress of thousand cankers will vary due to several factors, notably the susceptibility of the host. There appears to be a considerable range of TCD susceptibility among various "Juglans" species with "Juglans nigra" (black walnut) being particularly susceptible. Conversely, Arizona walnut ("Juglans major") appears to be quite resistant to the disease, with bark beetle attacks largely limited to small diameter branches, the fungus growing to a very limited extent, and effects of the disease rarely, if ever, progressing to involve large areas of the tree. Similarly southern California walnut ("Juglans californica") and little walnut ("Juglans microcarpa") may show fairly high resistance. Northern California walnut ("Juglans hindsii") and the commercial nut-producing Persian (English) walnut ("Juglans regia") apparently show various degrees of intermediate TCD susceptibility.

Citrus Black Spot is a fungal disease caused by Guignardia citricarpa. This Ascomycete fungus affects citrus plants throughout subtropical climates, causing a reduction in both fruit quantity and quality. Symptoms include both fruit and leaf lesions, the latter being critical to inter-tree dispersal. Strict regulation and management is necessary to control this disease since there are currently no citrus varieties that are resistant.

It has been observed in spiny lobsters ("Panulirus ornatus") in Vietnam, where it is caused by a species of "Fusarium".

It has been observed in shrimp, where the agent is microscopic protozoan "Hyalophysa chattoni" or a close relative, in Galveston Bay, Texas and other locations.

Thousand cankers disease is a recently recognized disease of certain walnuts ("Juglans" spp.). The disease results from the combined activity of the walnut twig beetle ("Pityophthorus juglandis") and a canker producing fungus, "Geosmithia morbida". Until July 2010 the disease was only known to the western United States where over the past decade it has been involved in several large scale die-offs of walnut, particularly black walnut, "Juglans nigra". However, in late July 2010 a well-established outbreak of the disease was found in the Knoxville, Tennessee area. This new finding is the first locating it within the native range of its susceptible host, black walnut.

Apple scab is a disease of "Malus" trees, such as apple trees, caused by the ascomycete fungus "Venturia inaequalis". The disease manifests as dull black or grey-brown lesions on the surface of tree leaves, buds or fruits. Lesions may also appear less frequently on the woody tissues of the tree. Fruits and the undersides of leaves are especially susceptible. The disease rarely kills its host, but can significantly reduce fruit yields and fruit quality. Affected fruits are less marketable due to the presence of the black fungal lesions.

White band disease causes the affected coral tissue to decorticate off the skeleton in a white uniform band for which the disease was given its name. The band, which can range from a few millimeters to 10 centimeters wide, typically works its way from the base of the coral colony up to the coral branch tips. The band progresses up the coral branch at an approximate rate of 5 millimeters per day, causing tissue loss as it works its way to the branch tips. After the tissue is lost, the bare skeleton of the coral may later by colonized by filamentous algae.

There are two variants of white band disease, type I and type II. In Type I of white band disease, the tissue remaining on the coral branch shows no sign of coral bleaching, although the affected colony may appear lighter in color overall. However, a variant of white band disease, known simply as white band disease Type II, which was found on Staghorn colonies near the Bahamas, does produce a margin of bleached tissue before it is lost. Type II of white band disease can be mistaken for coral bleaching. By examining the remaining living coral tissue for bleaching, one can delineate which type of the disease affects a given coral.

Skeletal eroding band (SEB) is a disease of corals that appears as a black or dark gray band that slowly advances over corals, leaving a spotted region of dead coral in its wake. It is the most common disease of corals in the Indian and Pacific Oceans, and is also found in the Red Sea.

So far one agent has been clearly identified, the ciliate "Halofolliculina corallasia". This makes SEB the first coral disease known to be caused by a protozoan. When "H. corallasia" divides, the daughter cells move to the leading edge of the dark band and produce a protective shell called a lorica. To do this, they drill into the coral's limestone skeleton, killing coral polyps in the process.

A disease with very similar symptoms has been found in the Caribbean Sea, but has been given a different name as it is caused by a different species in the genus "Halofolliculina" and occurs in a different type of environment.

Bacterial leaf streak (BLS), also known as black chaff, is a common bacterial disease of wheat. The disease is caused by the bacterial species "Xanthomonas translucens" pv. undulosa. The pathogen is found globally, but is a primary problem in the US in the lower mid-south and can reduce yields by up to 40 percent. BLS is primarily seed-borne (the disease is transmitted by seed) and survives in and on the seed, but may also survive in crop residue in the soil in the off-season. During the growing season, the bacteria may transfer from plant to plant by contact, but it is primarily spread by rain, wind and insect contact. The bacteria thrives in moist environments, and produces a cream to yellow bacterial ooze, which, when dry, appears light colored and scale-like, resulting in a streak on the leaves. The invasion of the head of wheat causes bands of necrotic tissue on the awns, which is called Black Chaff.

The disease is not easily managed, as there are no pesticides on the market for treatment of the infection. There are some resistant cultivars available, but no seed treatment exists. Some integrated pest management (IPM) techniques may be used to assist with preventing infection although, none will completely prevent the disease.

Coral has a symbiotic relationship with zooxanthellae that provide the coral glucose, glycerol, and amino acids. Under certain water conditions, like fluctuating temperatures and increased nitrogenous waste, corals will appear stressed. Also, these conditions allow for bacteria to grow inside the coral and compete with zooxanthellae. The bacteria produces the characteristic pale yellow lesions and eventually kills the zooxanthellae by impairing its mitosis and its ability to carry out photosynthesis. Yellow-band disease is found on coral reefs in the Caribbean.

The smuts are multicellular fungi characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled, and dust-like teliospores. They are mostly Ustilaginomycetes (of the class Teliomycetae, subphylum Basidiomycota) and can cause plant disease. The smuts are grouped with the other basidiomycetes because of their commonalities concerning sexual reproduction.

Smuts are cereal and crop pathogens that most notably affect members of the grass family ("Poaceae"). Economically important hosts include maize, barley, wheat, oats, sugarcane, and forage grasses. They eventually hijack the plants' reproductive systems, forming galls which darken and burst, releasing fungal teliospores which infect other plants nearby. Before infection can occur, the smuts need to undergo a successful mating to form dikaryotic hyphae (two haploid cells fuse to form a dikaryon).

False melanose lesions are characterized by many small, tan, slightly raised lesions. The lesions are much smaller than the hard spot variety with an average diameter of less than 1 mm (.04 in).

They are found on unripe fruit and are difficult to observe later in the season. Unlike hard spot lesions, no pycnidia are present.

There are multiple sources known to cause black gill disease. Poor pond conditions can cause debris to build up in the gills turning them black. Certain kinds of bacteria and the fungus genus Fusarium are also known causes.

As with other enterotoxemias, the disease leads to sudden death. Nevertheless, sheep with previous vaccination can show a protracted course. The rest of the flock may show loss of appetite and pica.

Peritoneal and thoracic cavities contains a great quantity of fluids, as does the pericardial sac.

The liver is sometimes swollen with perihepatitis. There appear a great number of necrotic foci, 3 to 4 mm diameter, which extend deeply in the organ. Hepatic lymph nodes are enlarged. The gallbladder is full.

Subcutaneous tissues are full of cyanotic venous blood. They may darken the hide, hence the name "black disease".

Bacterial leaf streak is a pathogen known to infect and damage wheat varieties. The pathogen has also been known to infect other small grain all cereal crops such as rice, barley and triticale. The strains of the pathogen are named differently according to the species they infect. It is one of the most destructive diseases in rice.

Resistant wheat cultivars offer the best protection against yield loss, but little is known about the inheritance of resistance. The disease is most common on wheat and can be found on winter and summer wheat varieties.

Symptoms of this pathogen can be seen on the stem, leaves, and glumes. Stem symptoms are not always present, but can be seen as a dark brown to purple discoloration on the stem below the head and above the flag leaf. In the early stages of the disease, translucent water soaked streaks can be seen on the leaves often accompanied by a shiny glaze or clumps of dried bacteria on the leaf surface. These markings turn to brown lesions after just a few days, and may be surrounded by a lime green halo. Lesions can stretch the entire leaf blade.

BLS exhibits similar symptoms to those of "Septoria nodorum", a common fungal infection. A common sign that will distinguish this pathogen from "Septoria nodorum" is the lack of spores on the leaves, which appears as tiny black spots on the leaf surface with a "Septoria" infection. A cream to yellow colored bacterial ooze produced by BLS infected plant parts is also a distinguishing sign of the pathogen.

Infected glumes, known as black chaff, are darkened and necrotic. Severe symptoms will result in kernels that are discolored due to black and purple streaks. Plants infected with bacterial leaf streak will exhibit an orange cast from leaf symptoms and suffer yield and quality loss.

Piedra (also known as "Trichosporosis") is a hair disease caused by a fungus.

Types include:

- White piedra

- Black piedra

Coral diseases mostly take the form of a narrow band of diseased tissue separating the living tissue from the exposed skeleton. The band moves across the surface of the colony at the rate of a few millimetres a day, leaving behind bare skeletal material that is rapidly colonized by algae.

Many of the diseases that affect corals are known by their most obvious symptoms such as black band disease, white pox and yellow-band disease. However in many instances it has not been possible to identify the pathogens responsible for the disease and culture them in the laboratory; that the coral is sick and the tissue is necrotic is apparent, but whether the fungi or bacteria present caused the disease or merely fed on the already dying tissue is not clear. There is also a minute crab a millimetre or so wide which is often associated with diseased corals, but whether it introduces the disease or just moves in to consume the necrotic tissue is uncertain. Some of the bacteria found on diseased corals are terrestrial species that are not normally considered pathogenic. Further research has shown that viruses may be involved in white plague infections, the coral small circular single-stranded DNA (ssDNA) viruses being present in association with diseased tissue. Viruses in this group are known to cause disease in some plants and animals.

So far one agent has been identified, the ciliate protozoan "Halofolliculina corallasia". Skeletal eroding band is the first recorded disease of corals that is caused by a protozoan, and thus the first known to be caused by an eukaryote – most are caused by prokaryotic bacteria. For example, black band disease is caused by microbial mats of variable composition, and White pox disease by the bacterium "Serratia marcescens".

"H. corallasia" is a protozoan that secretes a bottle-like housing called a lorica (Latin for cuirass, flexible body armor), that is anchored to a surface and into which the cells retract when disturbed. When a mature individual cell division divides, it produces a pair of worm-like larvae that settle on undamaged coral just ahead of the black band. There each daughter cell secretes its lorica, at the same spinning to produce the lorica's flask-like shape. This spinning, combined with the chemicals that harden the lorica, crumble the coral skeleton and kill the polyps. The discarded loricae of the "parent" "H. corallasia" cells remain, leaving the distinctive spotted region in the wake of the living black band.

The symptom of black pod disease is the necrotic lesion on the cocoa pod with brown or black color, which eventually enlarged to cover the whole pod. White mycelia growth on lesions that appeared several days after infection is the sign for the causal pathogen of black pod disease, which is "Phytophthora spp".

Black pod disease starts when the infected pod shows some little yellow spots, which eventually turn brown and enlarge to a dark brown or black lesion within five days. The lesion is fast growing and covers the entire pod after eighth day of infection. The infection does not only occur on the pod surface, but also invades inside the pod affecting the beans. The growth of white mycelia on black pod is visible after 11 days and the sporulation is initiated. The dispersal of sporangia or zoospores through water, ants and other insects occurs at this stage and will infect other healthy pods nearby. Direct contact of a black pod with healthy pods also leads to the spread of disease. In addition, the infected flower cushion and mummified pods are the locations for "P. palmivora" survival during dry season, where the pathogen will grow and continue to infect other developing pods

The infection occurs on any stage of pod development, where it causes wilting and dying of young pods and destroyed the beans of mature pods. The fully infected pods (the mummified pod), which then become dehydrated, are capable of providing the inoculum of "P. palmivora" for at least 3 years. "P. megakarya" causes the same symptom as "P. palmivora", but the occurrence is faster and generally produces greater amount of spores. Both "P. palmivora" and "P. megakarya" also caused canker on bark, flower cushion and chupons, and cankers on the base could extend to the main roots. Cankers were identified as one of inoculum sources for black pod disease. Furthermore, the pattern of infection caused by "P. megakarya" starts from the ground and moves up to the canopy, however there is no distinct pattern of disease infection caused by "P. palmivora" was reported. This pattern of infection could be due to "P. megakarya" and "P. palmivora" that were found to survive in soil and "P. megakarya" could be surviving in the roots of a few species of shade trees found in cocoa plantation.