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Powdery Mildew Assails Summer Squash

August 17, 2010

Powdery Mildew assails the Summer Squash

Powdery mildew, a white fungus, is attacking my summer squash!  This is pretty common this time of year as powdery mildew develops in hot temperatures!  Luckily, most of my squash has already fruited and is mature enough to harvest.  Once I’ve harvested enough squash I just remove the affected plants from my garden.  I do this mostly because I don’t want it to spread to other healthy plants, but also because it looks pretty bad.

A few facts:

  • Powdery Mildew is one of the most widespread diseases affecting many types of plants.  Members of the Nightshade Family, Cabbage Family and Squash Family can all be affected. 
  • Powdery Mildew can be easily identified as white to gray spots of growth on leaves.  These spots resemble baby powder and will rub off on your fingers after gently rubbing the leaves. 
  • Unlike other fungus, powdery mildew does not need standing water for spore germination.
  • Powdery Mildew doesn’t usually grow on the fruits of vegetables, though severely infected plants may have reduced yields, shorten production times and fruit that has little flavor.

Cultural Practices for Prevention and Control of Powdery Mildew

Things to remember for next spring!

  • Many plants have been developed to be resistant to powdery mildew.  When looking for seeds or vegetable seedlings be sure to ask for resistant varieties of cantaloupe, cucumbers, melons, peas, pumpkins, radish and squash.
  • Plant in sunny areas as much as possible and provide for good air circulation by maintaining adequate space between plants.

What you can do now:

  • As plants mature, selectively prune overcrowded plant material to help increase air circulation.
  • Remove or destroy all infected plant parts.  The fungus can overwinter in infected plants, so it is important to remove these plants from your garden.  Do not try to compost, as most compost piles do not reach temperatures hot enough to kill the fungus. 
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