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Plants, too, get PMS — powdery mildew syndrome

Published 7:30am Monday, July 23, 2012 Updated 1:34pm Monday, July 23, 2012

While plants don’t get hysterical, cry at the drop of a cup or yell at the kids for no good reason, they do have P.M.S; that is, plant powdery mildew syndrome. In plants, like women, it is very easy to diagnose and one of the hardest to manage.

Powdery mildew is that dreaded white powdery coat that suddenly shows up on your favorite phlox during hot, humid weather, that coats the leaves of your lilacs, your roses, or even your squash.

It may surprise you to know that in each of these cases, the disease is a different pathogen. In other words, the mildew on your rose won’t infect your phlox.

However, the white coat on the squash can also infect your pumpkins as they are in the same family.

Another that isn’t too fussy will affect, the mints i.e. bee balm

rudbeckia and the snapdragons. All powdery mildews are obligate parasites, meaning that they need a live host for the infection to feed on.

They won’t kill the plant as that would be suicide, but it may lead you to want to murder the affected plant as they really look ugly.

And to top offthe problem, it can be spread by wind, especially in humid weather.

P.M.S. on shrubs can kill young shoots but is not a problem on mature leaves. If it comes in on young, developing leave shoots and flowers, the leaves may be severely affected.

The young leaves will be crinkled, cupped up or otherwise distorted. Young flowers and fruit that are completely covered may even be killed.

The fungi survive in our winters by colonizing young tissue within the plant buds and starts up new infections as soon as the buds open in the spring.

A severely affected shrub that has a few very severely infected young shoots next to completely healthy shoots, probably has had the fungi in its’ buds all winter.

So, what to do. First of all, P.M.S. doesn’t kill its’ host. An infected

shrub should have the infected parts pruned off and removed from the garden.

Next, air circulation. This is important for the health of all plants. That is why weeding is so important.

Never grow susceptible plants in shade, or water lovers where they can dry out easily. Don’t over fertilize as that encourages tender succulent growth that is more susceptible to foliar diseases.

Fungicides will only stop the infection, not reverse it. If you are into chemicals, Fungonil and Saconil are usually readily available. Two organic chemicals are Kaligreen and First Step-Note.

A home remedy long used in New Zealand to stop P.M.S. on grapes and melons is: 1cup of milk, any kind, to 1 gallon of water and a drop or 2 of sticker or liquid dish soap. Baking soda is only slightly effective and can be toxic to some plants.

Thanks to Janna Beckerman, extension plant pathologist for much of this information. Who said gardening was easy.


Bev Johnson is an Otter Tail County Master Gardener

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