Biological Pests

Moulds

What are they and what do they need to live?

Moulds are simple plants which do not require sunlight for their existence. But they require organic material as a food source, and water if they are to grow and reproduce.

We are familiar with fungi as harmful organisms: in the form of moulds, diseases of crops and fungal infections. But humans have also used mould very productively in the fermentation of beer, production of cheeses and antibiotics, and as a food source—mushrooms.

Fungi feed on organic material; and museums, galleries and libraries are full of organic materials. Provided there is sufficient moisture available in the material or in the atmosphere, they will feed on:

• leather

• cotton

• wool

• paper

• wood

• bark

• fur

• rawhide

• photographic emulsions

• some varnishes and glazes

• adhesives

• some pigments

Under suitable conditions they will also grow on metal and stone surfaces, particularly those with a coating of dust or organic debris. Some species will grow on creosote-treated wood, or will even incorporate poisonous, chlorine-containing compounds into their diets.

Fungi can tolerate extreme temperatures—some species are known to survive in temperatures as low as -10⁰C and as high as 110⁰C.

Fungi and moulds are more affected by relative humidity than by temperature. A few species survive at relative humidities below 60%, but the majority require a relative humidity of at least 65% to survive and reproduce. If relative humidity drops below 60%, the fungal body normally dies; but the spores usually released at the time of such adversity lie dormant until the conditions are suitable for growth again.

Fungi and moulds survive best in environments where there is little disturbance and where air-flow is low. Such environments are found underneath suspended floors and in cellars, and can be present in store rooms and cupboards, or where objects are stacked very closely together.

Where do they come from?

Most people at one time or another have seen mould growing on old bread, cheese, jam, damp wood or leather. This growth, usually appearing as a fine, fluffy mass on the surface of such materials, is called the mould colony.

This mould colony appeared as thick multicoloured lumps. Photograph courtesy of Artlab Australia

If you look at a thriving colony under a microscope it is possible to see fruiting bodies. These structures contain the individual reproductive bodies called spores. The fruiting bodies stand up above the mass of the colony—so that the spores can be discharged unhindered into the atmosphere and be carried away by air currents.

Mould spores are microscopic in size, but are produced in very large numbers. They are everywhere—in the air we breath, on every surface around us, on our skin and on every object we value.

Under favourable environmental conditions the spores absorb water and grow. They grow rapidly and branch repeatedly—forming a new mould colony. When the colony is established and large enough, the fruiting structures appear, spores are produced and the cycle is repeated.