Leaf rust is a fungal disease of barley caused by "Puccinia hordei". It is also known as brown rust and it is the most important rust disease on barley.

Pustules of leaf rust are small and circular, producing a mass of orange-brown powdery spores. They appear on the leaf sheaths and predominantly on the upper leaf surfaces. Heavily infected leaves die prematurely.

Fusarium wilt is a common vascular wilt fungal disease, exhibiting symptoms similar to Verticillium wilt. The pathogen that causes Fusarium wilt is "Fusarium oxysporum" ("F. oxysporum"). The species is further divided into forma specialis based on host plant.

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.

Strawberry foliar nematode is a disease common in strawberries and ornamental plants that can greatly affect plant yield and appearance, resulting in a loss of millions of dollars of revenue. Symptoms used to diagnose the disease are angular, water soaked lesions and necrotic blotches. "Aphelenchoides fragariae" is the nematode pathogen that causes the disease. Its biological cycle includes four life stages, three of which are juvenile. The nematode can undergo multiple life cycles in one growing season when favorable conditions are present. They can infect the crowns, runners, foliage, and new buds of the plant via stylet penetration or through the stomata. The best management practices for this disease are sanitation, prevention of induction of the pathogen to the environment, and planting clean seed or starter plants.

Wheat yellow rust ("Puccinia striiformis" f.sp. "tritici"), also known as stripe rust, is one of the three wheat rust diseases principally found in wheat grown in cooler environments. Such locations are generally associated with northern latitudes or cooler seasons.

As R.P. Singh, J. Huerta-Espino, and A.P. Roelfs say in their (undated) comprehensive review of literature on the wheat rusts for UN FAO:

"Although Gadd first described stripe rust of wheat in 1777, it was not until 1896 that Eriksson and Henning (1896) showed that stripe rust resulted from a separate pathogen, which they named P. glumarum. In 1953, Hylander et al. (1953) revived the name P. striiformis."

Beet vascular necrosis and rot is a soft rot disease caused by the bacterium Pectobacterium carotovorum" subsp. "betavasculorum, which has also been known as "Pectobacterium betavasculorum" and "Erwinia carotovora" subsp. "betavasculorum". It was classified in the genus "Erwinia" until genetic evidence suggested that it belongs to its own group; however, the name Erwinia is still in use. As such, the disease is sometimes called Erwinia rot today. It is a very destructive disease that has been reported across the United States as well as in Egypt. Symptoms include wilting and black streaks on the leaves and petioles. It is usually not fatal to the plant, but in severe cases the beets will become hollowed and unmarketable. The bacteria is a generalist species which rots beets and other plants by secreting digestive enzymes that break down the cell wall and parenchyma tissues. The bacteria thrive in warm and wet conditions, but cannot survive long in fallow soil. However, it is able to persist for long periods of time in the rhizosphere of weeds and non-host crops. While it is difficult to eradicate, there are cultural practices that can be used to control the spread of the disease, such as avoiding injury to the plants and reducing or eliminating application of nitrogen fertilizer.

The fungal pathogen "Fusarium oxysporum" affects a wide variety of hosts of any age. Tomato, tobacco, legumes, cucurbits, sweet potatoes and banana are a few of the most susceptible plants, but it will also infect other herbaceous plants. "Fusarium oxysporum" generally produces symptoms such as wilting, chlorosis, necrosis, premature leaf drop, browning of the vascular system, stunting, and damping-off. The most important of these is vascular wilt. Fusarium wilt starts out looking like vein clearing on the younger leaves and drooping of the older lower leaves, followed by stunting of the plant, yellowing of the lower leaves, defoliation, marginal necrosis and death of the plant. On older plants, symptoms are more distinct between the blossoming and fruit maturation stages.

"Fusarium oxysporum" is split into divisions called "formae speciales" (singular "forma specialis", abbreviated "f.sp."). There are over 100 formae speciales divisions, each with one or two different races. Each forma specialis within the species are host-specific (i.e. specific to a certain plant) and produce different symptoms:

"F. oxysporum" f. sp. "batatas" affects sweet potato. The symptoms include leaf chlorosis, stunting, and leaf drop. It is transmitted through the soil and through vascular wounds in plant material.

"Fusarium oxysporum" f. sp. "canariensis" causes Fusarium wilt of Canary Island date palm and other propagated palms. The disease is spread through contaminated seed, soil, and pruning tools.

"F. oxysporum" f. sp. "cubense" causes Panama disease on banana. It is found everywhere bananas are grown in Africa, Asia, Central and South America. It attacks banana plants of all ages and spreads mainly through the soil. It causes wilting and yellowing of the leaves.

"F. oxysporum" f. sp. "lycopersici" causes vascular wilt in tomato. The disease starts out as yellowing and drooping on one side of the plant. Leaf wilting, plant stunting, browning of the vascular system, leaf death, and lack of fruit production also occur.

"F. oxysporum" f. sp. "melonis" attacks muskmelon and cantaloupe. It causes damping-off in seedlings and causes chlorosis, stunting and wilting in old plants. Necrotic streaks can appear on the stems.

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.

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.

Symptoms can be found on both beet roots and foliage, although foliar symptoms are not always present. If present, foliar symptoms include dark streaking along petioles and viscous froth deposits on the crown which are a by-product of bacterial metabolism. Petioles can also become necrotic and demonstrate vascular necrosis. When roots become severely affected, wilting also occurs. Below ground symptoms include both soft and dry root rot. Affected vascular bundles in roots become necrotic and brown, and tissue adjacent to necrosis becomes pink upon air contact. The plants that do not die completely may have rotted-out, cavernous roots.

Various pathogens can cause root rot in beets; however the black streaking on petioles and necrotic vascular bundles in roots and adjacent pink tissue help to distinguish this disease from others such as Fusarium Yellows. Additionally, sampling from the rhizosphere of infected plants and serological tests can confirm the presence of "Erwinia caratovora" subs.

Muscardine is a disease of insects. It is caused by many species of entomopathogenic fungus. Many muscardines are known for affecting silkworms. Muscardine may also be called calcino.

While studying muscardine in silkworms in the 19th century, Agostino Bassi found that the causal agent was a fungus. This was the first demonstration of the germ theory of disease, the first time a microorganism was recognized as an animal pathogen.

There are many types of muscardine. They are often named for the color of the conidial layer each fungus leaves on its host.

In fields, symptomatic plants are recognized in patches or rows. They appear dwarfed, stunted, and brown in comparison to healthy plants. Local symptoms appear above ground, and plant leaves are typically distorted in shape, crinkled, and discolored with hard surfaces. They often have reduced flower size. Diseased plants typically have dead crowns and a shortened internode of the runners.

A classic leaf symptom is the appearance of angular, water-soaked lesions between the veins. The angular appearance results where the lesion edge and vein meet. In leaves with parallel venation, the length of the lesion progresses parallel to the direction of the vein. As lesions enlarge and leaf damage progresses, symptomatic leaf edges become dry, dead, and crinkled. Because infected strawberry plants are less vigorous in growth, the stolon does not grow well, which results in reduced fruit size and number. If the nematodes infect early in plant development, specifically when the buds are forming, the plant morphology will be dwarfed and distorted.

Once the nematodes destroy most of the leaf tissue, they leave the plant through wounds and natural openings in the leaf to find a new host to infect. The pathogen is easily transmitted through direct contact between the foliage of infected and non-infected plants. Nematodes can also move over large distances through soil transportation, as a result of human and animal movement, or through insect and bird travel.

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.

Velvet disease (also called gold-dust, rust and coral disease) is a fish disease caused by dinoflagellate parasites of the genus "Piscinoodinium", specifically "Amyloodinium" in marine fish, and "Oodinium" in freshwater fish. The disease gives infected organisms a dusty, brownish-gold color. The disease occurs most commonly in tropical fish, and to a lesser extent, marine aquaria.

The single-celled parasite's life cycle can be divided into three major phases. First, as a tomont, the parasite rests at the water's floor and divides into as many as 256 tomites. Second, these juvenile, motile tomites swim about in search of a fish host, meanwhile using photosynthesis to grow, and to fuel their search. Finally, the adolescent tomite finds and enters the slime coat of a host fish, dissolving and consuming the host's cells, and needing only three days to reach full maturity before detaching to become a tomont once more.

White plague is a suite of coral diseases of which three types have been identified, initially in the Florida Keys. They are infectious diseases but it has proved difficult to identify the pathogens involved. White plague type II may be caused by the gram negative bacterium "Aurantimonas coralicida" in the order Rhizobiales but other bacteria have also been associated with diseased corals and viruses may also be implicated.

Yellow red muscardine is caused by "Paecilomyces fumosoroseus". It can produce reddish patches on the external body and powdery masses of spores internally.

Feather duster budgerigars ("Melopsittacus undulatus"), sometimes called budgerigar mops, are budgerigars that have a condition characterised by overly long feathers that do not stop growing at usual periods, giving the bird the appearance of a feather duster. This condition is sometimes known as chrysanthemum feathering. The contour, tail and flight feathers do not stop growing, and they do not have the necessary barbs and barbules for the feather's structure to interlock. The shaft (calamus) is also curved, and so the feathers appear deformed and fluffed out. Individuals with this condition often appear less alert than nest mates. In addition, they are small and some have other defects such as microphthalmia. They lack vigour, often cannot fly and die within a year of hatching. There is no treatment for the condition; birds are often euthanized in the nest.

The condition may be a genetic disorder, caused by a herpesvirus, or perhaps caused by both.

Mees' lines or Aldrich–Mees' lines, also called leukonychia striata, are white lines of discoloration across the nails of the fingers and toes (leukonychia).

Leucism (; or ) is a condition in which there is partial loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes. Unlike albinism, it is caused by a reduction in multiple types of pigment, not just melanin.

They are typically white bands traversing the width of the nail. As the nail grows they move towards the end, and finally disappear when trimmed.

The lesions are most frequent on the lower limbs, but may occur anywhere on the body, including the hands, arms, torso and even the neck. They may vary in number and erupt in mass numbers.

They consist of irregular patches of orange or brown pigmentation with characteristic "cayenne pepper" spots appearing within and at the edge of old lesions.

There are usually no symptoms, although there may be some slight itching, but there is no pain.

The eruption may persist for many years. The pattern of the eruption changes, with slow extension and often some clearing of the original lesions.

Schamberg's disease, or progressive pigmented purpuric dermatitis, is a chronic discoloration of the skin which usually affects the legs and often spreads slowly. This disease is more common in males and may occur at any age from childhood onward. This condition is observed worldwide and has nothing to do with race or ethnic background.

In 1977, a disease of scleractinian corals appeared on reefs off the Florida Keys in the United States and was termed white plague. It caused white lesions and was shown to be an infectious disease, being particularly prevalent in "Mycetophyllia ferox". This disease caused little mortality and occurred sporadically, but was still present in the area in 1984. It is now known as white plague type 1.

In 1995, a new coral disease was described as an epizootic disease in the same reefs in the Florida Keys. Many species of coral found in the area were affected and the mortality rate of these was up to 38%. The pathogen involved was found to be a previously unknown species of bacterium in the order Rhizobiales, which was placed in the newly created genus "Aurantimonas" and given the name "Aurantimonas coralicida", and the disease was described as white plague type 2. The pathogen was isolated from a diseased colony of "Dichocoenia stokesi" and cultured in the laboratory, subsequently being used to inoculate two healthy colonies which then developed the disease. In the next few months, it had spread over of reef and was killing seventeen species of coral. Over the next four years, it spread further, but interestingly, was most severe in different regions each year.

However, white plague is an enigmatic disease. Further research cast into doubt the role of "A. coralicida" as a causative agent by finding that bacterium on healthy parts of colonies of "Orbicella annularis" affected by white plague disease but absent from diseased parts. In these diseased colonies, an α-proteobacterium similar to one which causes a disease in juvenile oysters has been implicated, being found on the diseased parts of the coral but not on the sound tissues. These anomalous findings may be caused by the fact that there are two or more diseases with similar symptoms, both known as white plague.

In 1999, a third and still more virulent variant appeared in the northern Florida Keys. White plague type III mostly affected "Colpophyllia natans" and "Orbicella annularis".

A white-plague like disease reported from the Red Sea in 2005 has been shown to be caused by a different bacterial pathogen, "Thalassomonas loyana". Further research has shown that viruses may be involved in white plague infections, the coral small circular ssDNA viruses (SCSDVs) being present in association with diseased tissue. This group of viruses is known to cause disease in plants and animals.