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Please have a look at these images of my zucchini plant:

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What disease is this and what is causing this? What are the solutions to counter this?

Location: India. Weather In May-June: Hot! > 95F days.

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You may want to add your location (as vague as you need it to be) to your profile, along with any climate info you may want to include. It helps when answering to know what kind of conditions you're working with. –  Ed Staub Jun 28 '12 at 14:12
    
@EdStaub. Thanks. Edited post to include this info. –  gatul Jun 29 '12 at 2:50
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2 Answers 2

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That looks like downy mildew. From "The Organic Gardener's Handbook of Natural Pest & Disease Control" (Bradley), p194:

  • Remove and destroy badly infected leaves.
  • Disease is worst in cool, wet weather; don't water in this weather. (Avoid wetting foliage in general when watering.)
  • Spraying with potassium bicarbonate may help control it.

See also Managing Downy Mildew in Cucurbits (Cornell University).

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While I think I also see some mildew close to the ground, most of the damage looks like leaf miners - but much, much worse than I've ever had experience with in our cooler climate. I don't find much good guidance for what to do at this point, for this year. When done with the plant, be sure to dispose of it - get rid of the pupae and larvae. Also, clear out nearby weeds that may be hosts.

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I have to wonder if the leaf miner damage is worse because the plants are already weakened by the mildew? –  bstpierre Jun 28 '12 at 11:53
    
@bstpierre - Yeah, or both are driven from other things - too much heat and water? Look at gatul's other posts. –  Ed Staub Jun 28 '12 at 14:11
    
Yes, good point, I'd guess maybe recently extra-wet weather. –  bstpierre Jun 28 '12 at 15:02
    
Yes, its hot. Please see edited post. –  gatul Jun 29 '12 at 2:51
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