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White spots on suash plant?

Posted: Fri Aug 27, 2010 2:21 am
by blackturninggreen
Hello, can anyone tell me what causes white spots on plant leaves and what to do organically? Will the soap spray fix this?

Posted: Fri Aug 27, 2010 3:18 am
by cynthia_h
Without a photo, I'd say the most likely culprit is powdery mildew.

Soap spray is usually effective vs. soft-bodied insects (aphids, ants, and others).

I personally use "the milk solution" vs. powdery mildew. Start with 10% milk, 90% water. Make a pint or a quart (in the U.S.). In the mathematically aware world, make a liter. Then add 1 Tb. (15 to 20 mL) plain yogurt with live cultures, stir it in, and wait 30 minutes to an hour for the lactobacillus bacteria to multiply. These are the actual agents of powdery mildew's destruction. Stir the whole thing again, put it into a spray bottle, and apply to the squash plant on the top of and underneath the leaves.

If 10%/90% doesn't do the trick, increase the proportion of milk to water, but don't exceed 50%/50%. It's my experience that you want some fat in the milk (low fat is fine). Skim milk didn't work for me, but some people here say that it does work for them. Maybe it was the addition of the yogurt (a 2010 modification) that made the difference.

There's also a baking-soda preparation that can be used vs. powdery mildew, but I haven't used it. The "Search the Forum" function, just to the left of the "Log Out" option, can help you find the specifics. :D

But this is all based on a hypothesis which is, ATM, unsupported by evidence and supported only by the mathematical probabilities....

Cynthia H.
Sunset Zone 17, USDA Zone 9

Thanks for the infor

Posted: Sat Aug 28, 2010 4:31 pm
by blackturninggreen
I didn't think to put a photo in but powdery mildew seems to fit well. What ususally causes this? I will try the milk solution and let you know how it goes. Thanks

Posted: Sun Sep 05, 2010 8:21 pm
by garden5
Powdery mildew is a fungal disease that is usually brought on by wet, humid conditions, though I'm fairly certain that insects can spread it, as well. You'll find that most people get it eventually, though I will admit that it's much better to get it later rather than earlier.

Posted: Sat Sep 11, 2010 12:10 am
by organo
Although typically recommended for soft bodied insects, soap will actually work against powdery mildew by changing the leaf surface ph.

Bacillus subtilus sold as serenade is a organic biological treatment.

Copper sulfate/soaps will also work and are an organic option.

If things get extreme you can use a non organic product that contains captan.