Re: [tomato] Organic preventative for Late Blight??

Lazaro E. P. Peres (
Tue, 27 Apr 1999 21:41:55 -0300

I think that the ancient mix copper sulfate + calcium hydroxide could be
used. It protect the plant against many pathogens (fungus and bacteria) and
is a source of the macronutrients calcium and sulfur and of the
micronutrient copper. However, it will combat the fungus only if sprayed
before the infestation (its a protective fungicide).

Mix 10 g of CuSO4 (copper sulfate) with 7 g of Ca(OH)2 (calcium hydroxide)
and 1 liter of water. Adjust de pH to 6-7 (use indicator paper). If acid,
you can use more Ca(OH)2; if basic, use more CuSO4.

It has low toxicity and although it is really a mix of inorganic salts, I
think it could be considered a "organic" product.

Lazaro Peres
Sao Paulo - Brazil.

> From: Greg Park <>
> To: tomato newsgroup <>
> Subject: [tomato] Organic preventative for Late Blight??
> Date: Segunda-feira, 26 de Abril  de 1999 16:43
> Hi all,
> Well late blight struck this past weekend in So California.  I had a 18"
> tall champion hybrid tomato plant doing quite nicely until early last
> It had nice foliage and was a lush until I noticed some oily looking dark
> gray spots.  I went looking for an organic fungicide and was given a neem
> oil spray by my local nursery.  I sprayed the plant as per the
> Now this plant is planted at my work so I didn't see it over the weekend.
> When I left, the lower leaves were probably half covered by the blight,
> the top, newer foliage seemed unaffected.  I gave it a nice good deep
> watering before leaving.  The weather here during the weekend was
> but no rain.
> Upon return to work today, most of the plant was burnt up.  The main stem
> still green and the plant is not wilting.
> I'm starting to feel that it's impossible to grow tomatoes here without
> use of chemical fungicides...Does anyone know of a good organic fungicide
> that EFFECTIVELY combats early/late blight?
> Thanks and best regards,
> Greg Park
> Zone 10, Los Angeles, CA
> CEO-in-Training
> Park Steel Company, Inc.