What is powdery mildew?
Powdery mildew can come from several different types of genera such as Erysiphe, Golovinomyces, Oidium, Podosphaera, or others. Each genera is highly specific, meaning that they only infect specific plant species. For example, the powdery mildew that infects squash plants will not infect roses. All powdery mildew fungi are obligate parasites, meaning they can only grow on living plant tissue.
What are the symptoms of mildew?
In general, mildew is found on the leaves, shoots, and sometimes flowers and fruits appearing as if those plant parts had been dusted with powder. The mildew inhibits photosynthesis and causes leaves to turn yellow, twist, distort, die, and fall off.
About powdery mildew in brief
Powdery mildew is visually distinct with its powdery, white to gray colored mycelium growth on the surfaces of leaves and sometimes other plant parts. While it can be seen commonly, keep in mind that it tends to be plant-specific, which fortunately can limit its broad impact.
Biological cycle of powdery mildew
The mycelia, or vegetative structure of the mildew, grows on the surface of the plant host. Powdery mildews produce microscopic structure called appressoria that help attach mycelia to the plant surfaces. From there, specialized hyphal outgrowths called haustoria penetrate host cells to absorb nutrients. Some species of fungus form hyphae that grow within host tissue itself, making it more challenging to eradicate from the plant.
Powdery mildew reproduces rapidly via asexual reproduction, producing conidia (asexual spores) within a short 3-7 days of infection, contributing to exponential growth. Sexual reproduction of powdery mildew often comes later in the growing season or after flowering, resulting in the production of ascocarps containing spores. Ascocarps are resistant to low temperatures, drought, and can survive harsh conditions. After an irrigation event, the ascocarps will release their spores.
Powdery mildew can survive through the winter as ascocarps or from dormant mycelium within infected plants.
Powdery mildew prefers a high relative humidity at night, low humidity during the day, and warm temperature between 70-80°F. The spores are carried by air currents and germinate on the leaf surface.
Prevention techniques
The best treatment against powdery mildew is prevention, since it can be difficult to eradicate completely. Maintain a clean growing area, clothes, footwear, equipment, and wash hands thoroughly before entering a grow area and periodically while working.
Avoid applying excess fertilizer, to limit the production of succulent tissue, which is more susceptible to powdery mildew. When conditions are favorable for powdery mildew, heat and ventilate in the late afternoon to reduce humidity during the night hours. Prune plants to allow greater airflow and ventilation within the plant canopy. Ensure the entire grow area is sufficiently ventilated.
Solutions for controlling powdery mildew
Remove infected materials from the growing area, seal completely, and dispose of it promptly. Horticultural oil applications containing thyme oil can reduce mildew. CANNA CONTROL is a naturally-derived, thyme oil based formula that effectively manages mildew. Additional application options include milk spray, baking soda spray, or apple cider vinegar spray. Sulfur burners can also be used.
