Mildew on a jasmine plant (C) Daniel FriedmanHow to Distinguish Between Mildew and Mold
Products labeled "mildewcide" and findings of "mildew" in buildings are speaking a bit loosely
     

  • MILDEW PHOTOGRAPHS BUILDINGS ? - CONTENTS: What's the difference between "mold" and "mildew" - does it matter? Although many people refer to a mildew odor or to finding mildew on books, clothes, or in buildings, that's a mistake. Here we explain why mildew doesn't grow on or in buildings (except on plants) and why you should care.
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What's the difference between mold & mildew? This article explains the difference between mildew and mold (or other forms of mold). As we discuss in this article, mildew, a sub-class of molds, is an obligate parasite that grows only on living plants, and is generally white in appearance.

Our page top photograph shows mildew growing on a jasmine plant at a Vassar College home in Poughkeepsie, New York. More photographs of mildew are included in this article.

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What's the Difference between "Mold" and "Mildew"?

Mildew on a Jasmine plant, closeup (C) Daniel Friedman Mildew on a Jasmine plant, closeup (C) Daniel Friedman

Our closeup photographs above show powdery mildew growing on the leaves of a jasmine plant. Mildew is a specific type of mold that grows on living plants. Just on plants. Notice that this mold (mildew) is white? Mildew is always white or perhaps light gray in color.

Article Contents

Mildew spores (C) Daniel FriedmanMildew: Mildew is a proper subset of the broader mold family. It is a plant parasite.

Among the major groups of molds is a very large mold family, Basidiomycota (or basidiomycetes); this family in turn includes, among the many Basidiomycota members, we find a relatively small sub-group, the Ustilaginales, also familiarly called Smuts and Mildews.

Both smuts and mildews are parasites of living plants (in mycological terms these are obligate biotrophic pathogens) that cause serious crop damage as well as damage to ornamental shrubs, flowers, etc. See Kiss et als. for an example of mildew damage to tomatoes.

At left, a lab photo of mildew spores collected from the jasmine plant at page top. To understand our comment that mildew does not grow in or on buildings, notice our use of the words obligate biotrophic pathogens - meaning that these fungi are pathogens that grow only on living plants and that they cause a disease in the plant.

Here is a Photo of An Indoor Mold Contamination - that is Not Mildew

Photograph: typical mold on basement drywall after a basement flooding event -  © Daniel FriedmanMold: In general, mold is a term encompassing a very wide family of organisms (the Fifth Kingdom) that includes more than a million and a half species.

Lots of molds grow on lots of different organic substances, under a variety of conditions of light and temperature, but all molds require moisture and something organic on which to grow (paper, wood, paint, cloth, leather, plastic, etc.).

Building mold contamination: although a very large number of molds may grow on various building surfaces and building contents, there are about 200 "bad boys" of mold commonly found contaminating buildings. None of these include the mildews.

See MOLD FREQUENCY in BUILDINGS for a table of the most common molds found in buildings, and

also see MOLD ATLAS & PARTICLES INDEX.

Our photograph (left) shows black, brown, and gray mold growing on drywall in a basement that was flooded. This is mold, but it is not mildew. Different mold genera/species might be growing on the wood framing or insulation materials inside this moldy wall.

There are mold genera or species that can grow on a remarkably wide range of organic materials that are found both outdoors and inside, and that can appear in an wide range of colors (black, brown, red, green, gray, white, orange, tan, yellow, for example) and textures.

Often specific mold genera or species prefer to grow on particular materials, so not all molds grow on all materials. (Most molds will not grow in mold culture media, for example.)

Some molds even grow on top of (and eat) other molds - parasitic molds. Molds are capable of breaking down cellulose, for which we should be thankful. Even though we don't like to find mold breaking down paper covered drywall (paper is made of cellulose), if we didn't have a mold kingdom on earth, we'd all be buried in tons of un-decayed dead plant matter.

Mildews are divided into two sub-groups, with quite a few sub-species

  1. Oidium-Erysiphe, familiarly named Powdery Mildew, and
  2. Peronosporaceae, familiarly named Downy Mildew

What Does Mildew Look Like

Though both of these groups may also include other species, they all look similar on plants - white or gray powdery or splotchy deposits on plant leaves and stems. Mildew may appear on the plant's buds, flowers, fruits, in sum, just about on any live plant tissue, though not so likely on heavy dry bark such as on tree bark or on woody stems. See our plant photographs earlier in this article.

Our lab microphotograph (above-left) shows the hyaline (colorless) spores of Oidium-Erysiphe that we collected from the jasmine plant shown in the photographs in this article. In the microscope, mildew spores (Oidium-Erysiphe) are colorless; on a plant this mold species appears as a white powdery substance.

In sum, mildew is a white powdery fungus that is an obligate parasite found on living plants.

Does Mildew Grow on or in buildings?

White Mold on an interior doorNo. Mildew grows on living plants.

But lots of people (incorrectly) call various building molds "mildew", and lots of mold cleanup products use the words mildew or mildewcide in their name and instructions.

A mycologist or a good text will tell you what substrates a particular mold has been known to grow on and which types of material it prefers.

For example, mildew is unlikely to be found ever growing on an indoor surface (except for a house plant), since mildew is a pair of sub-group of molds (powdery mildew and downy mildew) which grow only on living plants.

Our photograph of a white mold found growing on an indoor surface (left) is not mildew. It's a mold, but it is not mildew.

So you can see that indoor mold that your home inspector or "mold test expert" has called "mildew"

  • might be white but it is not mildew unless it is growing on a plant
  • might be other colors than white or gray, which means that it's certainly not mildew

Does it Matter Whether We Call Mold Found on or in a Building Mildew or Mold?

In a practical sense, making the mistake of calling an indoor or outdoor mold found on a building "mildew" is not a big deal. With the exception of avoiding spending on costly cleanup of harmless cosmetic molds or stains, the mold remediation and mold prevention procedures in a building are about the same regardless of mistakes in naming the mold.

You won't find mildew on or in a building on anything but a living plant, despite the names found on indoor or outdoor cleaning products that use the term "mildewcide" and "mildew-resistant product", or found in "mold reports" or in home inspections notwithstanding.

We think that mildew just a less scary name that some folks like to use to describe mold found in buildings, especially in real estate sales. We think that mildew is used on mold cleanup products or mold-resistant products also because of the widespread use of that word by consumers faced with an indoor mold problem.

What Does it Mean if Your Inspector or Mold Expert Calls it Mildew?

See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for help in deciding if you need a mold expert or not. But if your "mold expert" or home inspector tells you that s/he found mildew growing in or on the building, that person may be less of an expert on finding, identifying, and removing problem mold than you hoped, and therefore

  • The mold test consultant or mold inspector may not be adequately skilled in finding the most important reservoirs of mold contamination in the building.

    If the mold inspector does not understand the basic mycology of what kinds of mold are likely to grow where in a building under what conditions, the inspector is unlikely to know where to look for problem mold and is at risk of reporting superficial mold contamination while completely missing the more serious problem mold reservoir in the structure.

    We discuss this problem further at MOLD APPEARANCE - WHAT MOLD LOOKS LIKE,

    at MOLD FREQUENCY in BUILDINGS, and

    at FIND MOLD in buildings, HOW TO.
  • If the mold test or mold consultant fails to identify the important mold reservoir in the building, advice given to a building occupant's doctor about building mold exposure may be incorrect.
  • The home inspector, mold inspector, or mold remediator's advice on what to do about building mold might also be less than fully accurate.

    See MOLD KILLING GUIDE for an example of this problem, and also

    see MOLD CLEANUP - MISTAKES to AVOID.
  • The mold consultant may mistake cosmetic mold for problem mold, spending too much on a mold cleanup of the "wrong problem" in the building.

    See MOLD APPEARANCE - STUFF THAT IS NOT MOLD, and Black cosmetic mold.

At Distinction between "mold" and "mildew" on books we discuss more aspects why the difference between mold and mildew matters.

How do I Get Rid of Mildew?

If your "mildew" is found on building surfaces, it is mold, but it is not mildew, and you need to follow normal mold cleanup procedures.

See BASICS YOU NEED to FIND, TEST, REMOVE MOLD for a detailed step by step guide to removing problem mold and for identifying and fixing the cause of mold growth in the first place.

If you are having trouble tracking down a moldy smell in your building, try the suggestions we describe

at ODORS GASES SMELLS, DIAGNOSIS & CURE.

If your mildew is indeed growing on a living plant (tomatoes, grapes, crops, house plants, other plants) it can weaken or even kill the plant, at least by interfering with photosynthesis. Mildews on plants may be a species of mildew fungus that is plant specific. For example a mildew that grows on grapes may affect only those plants and may not infect nearby plants of other types, roses for example.

But the conditions that cause powdery mildew to grow on plants invite infection of many plants in a given area. These include crowding (poor air circulation within or around the plant), and dampness or high humidity. If a plant is already stressed or weak from other conditions, it may be more susceptible to mildew infection as well.

While lots of "mildew cleaning" products are sold with the intention of removing mold from building surfaces (bathtub tile grout, for example), do not use such products on plants - you will probably kill the plant.

See MILDEW REMOVAL & PREVENTION for details on what to do about cleaning off or removing mildew, and how to both cure and prevent mildew.

Mold on or In buildings - Molds that are Mistaken for Mildew

Photograph of paint failure details

 

Continue reading at MOISTURE CONTROL in buildings or select a topic from the More Reading links shown below.

Or see MILDEW REMOVAL & PREVENTION

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MILDEW PHOTOGRAPHS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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