Learn and Grow
Mold on Soil: Effects and Preventive Measures
The kind of climatic conditions we experienced in spring 2016, namely cold and humid weather with very little sun, were behind outbreaks of surface mold on greenhouse soils. Jean-Pierre Fortin (Ph.D.), Technical Director, explains their effect on plant growth and what measures to take to prevent their development.
The climatic conditions we experienced in spring 2016, namely cold humid weather and a lack of sunshine, were highly favourable to the development of surface mold on greenhouse soils. These humid, cool conditions are highly conducive to the germination of fungal spores. These spores are naturally present in the environment and in various types of organic matter, such as peat moss and compost. Their growth, however, does not come about until a particular set of conditions occurs: the presence of water, a source of food, the appropriate concentration of oxygen and a specific temperature. These conditions may arise from a variety of causes. They can be direct causes, such as the ambient humidity, irrigation and the temperature of the greenhouse, or indirect, such as humidity caused by dripping.
A number of species may develop, but those most often seen are saprophytic fungi, which feed on decomposing organic matter. We often find among others Cladosporium ssp, Peziza ostracoderma (peat mold), Peacilomyces sp and Chrysosporium Tropicum. The mycelium, which is the branching part of the fungi, is usually whitish or yellowish in colour. The older the mold is, the more new spores are visible, revealing more colourful hues in tones of yellow, brown, green or orange. During the period when favourable conditions are present, the white mycelium appears on a small part of the substrate, or it can be more widespread, sometimes even completely covering the soil surface.
The presence of mold may sully the appearance of soil, but generally does not cause any other problems. The fungal outbreaks, although troublesome, are in fact non-parasitic. Unlike the development of algae, mold does not impede wetting. Plant growth therefore proceeds normally. What’s more, fungi are ephemeral; they disappear quickly when dry, warm weather returns.
To prevent the occurrence of mold, the humidity in the greenhouse must be lowered.
- Raise the temperature during cold spells to reduce humidity in the greenhouse;
- Use anti-drip plastics;
- Monitor areas where dripping occurs and direct water to gutters to prevent soil from getting soaked;
- Avoid accumulation of water in soil; dry soils and the tops of growing tables;
- Keep soil as dry as possible, by surfacing greenhouse floors with concrete or by ensuring good drainage.