POWDERY MILDEW

This is powdery mildew, a fungus that is often found growing on the leaves and stems of plants. There are many different species and genera that affect a wide range of different plants. Powdery Mildew is a surface infection that does not directly harm the plants that it infects. However, if it spreads and covers enough of the plant it can block the leaves from receiving sunlight, stunting the plants’ growth and dramatically reducing yields.



Powdery Mildew is white in color and as its name suggests, has a powdery texture. It first appears as small round dots on the surface of the leaf or stem, which gradually grow until they form a solid white covering on the surface of the plant.



Heavily infected plants that are densely covered in the mildew will display stunted growth with deformed leaves, stems, and flower buds. Fruits and flower buds will often be aborted, but plants cannot be killed solely by the mildew.

Powdery Mildew prefers warm temperatures, low sunlight levels, and low humidity. It is a common problem in greenhouses, and once it gets established can grow on plants in a variety of habitats. The mildew spreads via spores and can quickly take over large numbers of plants.



The growth of Powdery Mildew is accelerated and worsened by the presence of sap-sucking insects such as aphids and whiteflies. These insects not only weaken the plants they feed on, making them more susceptible to infection, but also produce honeydew, a sugary substance that is left on the plant surface and which promotes the growth of the fungus. These insects will often carry spores with them, and their sucking mouthparts allow for easy inoculation of the plants, making them a significant disease vector for powdery mildew.


The fungus does not directly parasitize the plant itself, instead growing on the surface and subsisting off of exudates. However, large amounts of powdery mildew can block out sunlight and thus indirectly harm the plant, which in reduces the plants’ defense and allows the mildew to spread further. It will easily spread to any nearby susceptible plants, and can quickly infect large populations.

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