Mildew is a form of

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

. It is distinguished from its closely related counterpart, mould, largely by its colour: moulds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consisting of minute

hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

( fungal filaments) produced especially on living plants or organic matter such as wood, paper or leather. Both mould and mildew produce distinct offensive odours, and both have been identified as the cause of certain human ailments. In horticulture, mildew is either species of

in the order Erysiphales, or fungus-like organisms in the family '' Peronosporaceae''. It is also used more generally to mean mould growth. In

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th ...

, mildew meant honeydew (a substance secreted by

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s on leaves, formerly thought to distill from the air like dew), and later came to mean mould or fungus. Mildew grows on damp cloth, leather, or on plants, and growing on leaves can damage the plant.

Household varieties

The term mildew is often used generically to refer to mould growth, usually with a flat growth habit. Moulds can thrive on many organic materials, including clothing, leather, paper, and the ceilings, walls and floors of homes or offices with poor moisture control. Mildew can be cleaned using specialized mildew remover, or substances such as bleach (though they may discolour the surface). Oidio Plantas

There are many species of mould. The black mould which grows in attics, on window sills, and other places where moisture levels are moderate often is ''

Cladosporium ''Cladosporium'' is a genus of fungi including some of the most common indoor and outdoor molds. Species produce olive-green to brown or black colonies, and have dark-pigmented conidia that are formed in simple or branching chains. Many specie ...

''. Colour alone is not always a reliable indicator of the species of mould. Proper identification requires a microbiologist or mycologist. Mould growth found on cellulose-based substrates or materials where moisture levels are high (90 percent or greater) is often ''

Stachybotrys chartarum ''Stachybotrys chartarum'' (, ), also known as black mold or toxic black mold, is a species of microfungus that produces its conidia in slime heads. It is sometimes found in soil and grain, but the mold is most often detected in cellulose-rich b ...

.'' "Black mould," also known as "toxic black mould", properly refers to ''S. chartarum''. This species is commonly found indoors on wet materials containing cellulose, such as wallboard (drywall), jute, wicker, straw baskets, and other paper materials. ''S. chartarum'' does not, however, grow on plastic, vinyl, concrete, glass, ceramic tile, or metals. A variety of other mould species, such as ''

Penicillium ''Penicillium'' () is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production. Some members of the genus produce pe ...

'' or ''

Aspergillus ' () is a genus consisting of several hundred mold species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Mic ...

'', may appear to grow on non-cellulosic surfaces but are actually growing on the

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...

that adheres to these surfaces. Glass, plastic, and concrete provide no food for organic growth and as such cannot support mould or mildew growth alone without biofilm present. In places with stagnant air, such as basements, moulds can produce a strong musty odour. The pink "mildew" often found on plastic shower curtains and bathroom tile is actually a red yeast, '' Rhodotorula''.

Environmental conditions

Mildew requires certain factors to develop. Without any one of these, it cannot reproduce and grow. The requirements are a food source (any organic material), sufficient ambient moisture (a

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

of between 62 and 93 percent), and reasonable warmth ( to is optimal, but some growth can occur anywhere between freezing and ). Slightly acidic conditions are also preferred. At warmer temperatures, air is able to hold a greater volume of water; as air temperatures drop, so does the ability of air to hold moisture, which then tends to condense on cool surfaces. This can work to bring moisture onto surfaces where mildew is then likely to grow (such as an exterior wall). Preventing the growth of mildew therefore requires a balance between moisture and temperature. This can be achieved by minimizing the moisture available in the air. Air temperatures at or below will inhibit growth, but only if the

is low enough to prevent water condensation (i.e., the

dew point The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will ...

is not reached). With warmer temperatures, the water holding capacity of the air increases. This means that if the amount of water vapour in the warming air remains the same, the air will become drier (i.e. it has a lower

). This again inhibits fungal growth. Warm, growth-favoring temperatures coupled with ''high'' relative humidity, however, will set the stage for mildew growth. Air conditioners are one effective tool for removing moisture and heat from otherwise humid warm air. The coils of an

air conditioner Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...

cause moisture in the air to condense on them, eventually losing this excess moisture through a drain and placing it back into the environment. They can also inhibit mildew growth by lowering indoor temperatures. In order for them to be effective, air conditioners must recirculate the existing indoor air and not be exposed to warm, humid outside air. Some energy efficient air conditioners may cool a room so quickly that they do not have an opportunity to also effectively collect and drain significant ambient water vapour.

References

{{Reflist Building defects Plant pathogens and diseases

Household varieties

Environmental conditions

See also

References