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Powdery Mildew is a catch-all term for a variety of fungal infections in plants.  Everything from crape myrtles, roses, lilac, phlox, fruit trees, and vegetables may get it.  Some plants weather the problem, some plants are seriously injured and die.  It is easier to prevent the problem than to cure it.

Symptoms

The symptoms of powdery mildew are pretty straightforward.  There is a dusty white to gray coating over the leaves or other parts of the plant.  The coating starts in circular rings that expand outward like a supernova until they meet neighboring rings and form one continuous coat.  This usually happens late in the growing year in humid hot temperatures or when it is very wet from a lot of rain.  However, symptoms can occur at any time of the year.

Damage From Powdery Mildew

Powdery mildew causes stunting and distortion of the leaves, buds, growing tips, and fruit.  It can cause the death of the tissue it invades as it actually penetrates the surface of the plant.  This may cause the leaves to drop prematurely.  Since the fungus sucks nutrients out of the plant and causes the leaves, which help provide food for the plant, to drop, the plant can starve to death and die.

Life Cycle of Powdery Mildew

In order to get rid of powdery mildew, you need to understand its’ life cycle.  Fungi reproduce with spores that are spread in the wind.  The spores then survive the winter in black structures called cleistothecia.  These are on the plant or on debris such as leaves and stems on the ground.  When spring comes, or summer, depending on the climate, the sexual spores are shot up into the air from these structures and land on leaves or stems.  They then form the ashy powdery stuff that we see as powdery mildew.  In addition, the fungus produces asexual spores called conidia that help the fungus spread and infect more plants.

How to fix it

First, gather up all plant debris below and around the plant.  Do not compost this.  It should be placed in a trash bag for the trash man to pick up.  Without plant debris, the overwintering stage is hampered severely.  At the first sign of problems, a fungicide should be applied to the infected plant.  I cannot tell you which pesticide, because that is dependent on what the plant is and where it is growing.  However, your Extension Agent or nursery worker can recommend a product for you to use.

Catch Things Early

Severely infected plants may still die and will have to be destroyed.  However, the sooner you treat an infection, the better the survival rate.  This means you will need to inspect your plants regularly for problems.  Regular inspections are a good idea anyway.  They help you notice problems quickly so they can be treated before they get out of hand.

If you lose plants to powdery mildew and wish to replant, try to plant resistant varieties of those plants.  These plants are not immune to powdery mildew, but do fight it off better.  Most Extension Agents have a list of resistant varieties.  Good nurseries usually do as well.

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