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Close up of powdery mildew on a plant leaf

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This is first in a series of articles related to powdery mildiew.

What’s that powdery white stuff that’s suddenly appeared on your plants? Although it may look benign, it’s actually a fungal disease called “powdery mildew.”

What is this fungus?

Powdery mildew is a fungal infection that affects plants; it most often appears on the leaves of the plant, but can also affect stems, flowers and fruit. There are several different types of powdery mildew, but they all come from the fungal order Erysiphales. All powdery mildew infections produce similar symptoms.

What does it look like?

It first appears as small white or gray “powdery” patches or spots that look like talcum powder, usually on lower leaves and stems. This mildew can spread quickly as fungal spores multiply, covering the entire plant.

It will change color as it progresses, from white or gray to yellow-brown, and then black.

what causes this condition?

Powdery mildew fungus first takes hold on a plant’s surface (usually the leaves), where water content is high.

It can happen because of water stress, when water supply for plants is inadequate for a period of time.

It begins on the surface of the plant (usually the leaves) and then creates microscopic dispersal spores that go airborne.

Note: High humidity conditions are not needed to start or spread, as with some other fungal infections, although it does need high relative humidity. The spores have a high moisture content, which means they can infect more easily under drier conditions than most fungi can.

What are the symptoms?

Pinhead-sized spores first appear as white spots that look like talcum powder. These white spots multiply, turn a yellow-brown color, and finally turn black.

Your plants may look healthy when the infection first occurs, but can ultimately become discolored as the infection progresses. Because it hinders photosynthesis, powdery mildew will ultimately stunt growth and can even kill the plant.

Can you treat this fungus?

There are treatments for powdery mildew, although previously infected plants may not be suitable for harvest. More on treating and preventing it, next time.

additional resources

Understand the key factors that come into play when determining how to set up your cultivation. These will not only create efficiencies, these tips will help you avoid “Crop Crushers.”