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Thursday, September 16, 2010

We Got Mildew Yes We Do! We Got Mildew, How 'Bout You?

Here is an example of squash with just a few spots of powdery mildew.
 As tends to happen in the late summer, our squash is suffering from powdery mildew.  This problem is pretty easy to identify;  our plants will look like someone tossed some baby power all over them.

It starts small and then just gets worse if left to proliferate.  Powdery mildew sends little tubes into leaf cells to suck out their contents, killing the cells in the process. As leaf cells die and the leaf's surface becomes covered in the white fungus, photosynthesis is reduced and leaves may be lost. Crop volume and eating quality can be reduced.

Here the mildew has been left to keep growing!

So how do you get rid of it organically?  Well, there are quite a few options. 

PREVENTION
According to our own UC Davis Integrated Pest Management, prevention is always the best way to avoid this problem.  In other words, if your garden is prone to this kind of issue, next time you plant squash, melon, pumpkin, etc., be sure to start with a resistant variety.

CULTURAL PRACTICES
You can avoid powdery mildew my making sure your plants receive plenty of sun.  (Because of the location of these plants near the South Building of the Robert Mondavi Institute, these plants do get more shade than others.)  Also be sure to:
  • Provide good air circulation by not crowding your plants
  • Rotate squash beds on a minimum three-year cycle to reduce the chance of a fungal buildup or reinfection from one year to the next.
  • Pull up infected plants and burn or bury them.
We got the dummy whammie--the plants need more sun and they are not disease resistant varieties--so now what?

ORGANIC FUNGICIDES
According to UC Davis Integrated Pest Management, once you have the powdery mildew problem, oils, like neem oil,  tend to work better at eradicating the issue once you have it rather than preventing the problem. 

You may also want to try a biological fungicide like Serenade Disease Control Concentrate, but like UC Davis Integrated Pest Management states, "While this product functions to kill the powdery mildew organism and is nontoxic to people, pets, and beneficial insects, it has not proven to be as effective as the oils or sulfur in controlling this disease."

HOME REMEDY
For those of you interested in home remedies, it seems that you can also try making your own spray of one part skim milk to 9 parts water.  Skim milk works just as well as other types of milk--whole, low fat etc., but no fat means no odor!  Read more about this research finding here:  Using Milk to Control Powdery Mildew.

Did you get the gift of powdery mildew this summer?  If so, what did you do to get rid of it?  Let us know!

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