Thursday, August 26, 2010

For them - Water is Over-rated

Powdery Mildew on summer squash (Erysiphe cichoracearum)

These are no happy days for my summer squash - they are being "harassed" by powdery mildew.  There are different species of powdery mildew and they are plant-specific.  For example Erysiphe cruciferarum will infect crucifers while Erysiphe pisi prefers peas.  The pathogens that cause powdery mildew are unique from most leaf-infecting diseases because their spores do not require free water to germinate.  As a result they can infect their host plants in very dry condition such as ours. That is why in a time when blackspots and peach curl are all wiped off by the lack of moisture, powdery mildew is thriving happily.

The strength of this pathogen to withstand the lack of water can be totally reversed by water itself.  Hosing the leaves with water will do the trick depending on the severity or stage of the infection.  

Some literature on powdery mildew:


Tatyana@MySecretGarden said...

I've never heard about using water to fight powderly mildew! Thank you Helen for educating me! Our summer was unusually cool, and it looks like our squash will be very late.

Autumn Belle said...

I am very worried when I see powdery mildew on the leves. Luckily there is a cure that does not need the use of harmful chemicals.

Helen Lewis said...

Tatyana-- It's an old method which works well if done at the early stages of infection. Also, it is important to do it when the sun is up (between 10-2 pm)so that the leaves get dry quickly to avoid the proliferation of other diseases.

Thanks for your comment. I appreciate it.

Helen Lewis said...

Belle -- Yes you can go chemical free with the right technique. If you are dealing with few number of plants you might also hand spray them with dishwashing soap and water. On my roses I usually put four pumps of soap to a pint of water. This will disturb the growth of the spores.

Thank you for showing interest in my blog. I looked at your blog also and it is amazing. You are indeed a good photographer!

Curbstone Valley Farm said...

Considering how odd our summer weather has been, I'm surprised we haven't seen more powdery mildew here this year...not that there's not still time! I have used the dilute ivory soap method before with good success, but next time I might try just the hose!

Helen Lewis said...

Curbstone Valley-- I hope you'll not see the disease at all. It's always better to not have to deal with it...we get more time to do the fun stuff. :)

Anonymous said...

If powdery mildew is on a lettuce or chard leaf and you wash it off, is the leaf safe to eat?

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