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Powdery Mildew

by Stephanie Suesan Smith on September 4, 2010

Powdery mildew, a Biotrophic Fungus
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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, and fruit trees 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 straight forward.  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.

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 on 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 asesxual 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 burned if possible, or 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.  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.

What experiences have you had with powdery mildew?

 

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{ 6 comments… read them below or add one }

Ron from Sell Property Fast September 16, 2010 at 8:51 am

Oh no! I don’t know that disgusting dust like that’s appearing on my plants is powdery mildew and they actually ruining my baby plants? I am glad I found your post! I will run to my garden now and fix this thing! See you then.
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Loft Conversion London October 6, 2010 at 10:15 am

I am seeing powdery mildews on my plants, and I don’t know what to do. I am glad that I have found your post, I can use this to take care of my plants.
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Toenail Fungus Treatment Cure March 29, 2011 at 10:22 pm

Thanks for sharing such a wonderful post. I never knew that this white stuff is a fungal infection on plants.

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Jimmy from Flexible Solar Panels July 31, 2011 at 3:56 pm

That’s too bad that you have to use fungicide to get rid of this. I was hoping to find a natural way and not have to use chemicals. I’ll try getting rid of the debris first and see if that helps enough. It’s been raining here so much recently though. This stuff has been spreading like wildfire.
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Stephanie Suesan Smith August 1, 2011 at 6:37 am

You are probably the only one in the country getting rain. The rest of us are dry as tinder.

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Gavin Sell Property Fast November 6, 2011 at 8:42 am

I have been wondering for sometime what was wrong with the plant in my lounge and now from reading this page all has become clear! Thank-you

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