I have just picked my first tomatoes for 5 years, having lost all to
blight for the last 4 years.
This year for the first time I have used Bordeaux Mixture which is
suggested as the nearest organic control.
Now I am concerned about the white copper sulphate deposits on the
fruit.
Is copper sulphate toxic?

Does anyone know how thoroughly I need to wash them?
Has anyone else used BM? Advice is to spray weekly.

Pam in Bristol

In article ,
Pam Moore writes:
| I have just picked my first tomatoes for 5 years, having lost all to
| blight for the last 4 years.
| This year for the first time I have used Bordeaux Mixture which is
| suggested as the nearest organic control.
| Now I am concerned about the white copper sulphate deposits on the
| fruit.
| Is copper sulphate toxic?

Yes, but not catastrophically so. You need micrograms of copper
a day, the odd few milligrams on occasional will almost certainly
do no harm, and the lowest lethal dose recorded is of the order
of a gram.

| Does anyone know how thoroughly I need to wash them?

Moderately. No need to panic, but do wash them.

| Has anyone else used BM? Advice is to spray weekly.

Yes, on potatoes, where the problem doesn't arise. Weekly seems
a bit excessive, but the issue for tomatoes is whether there has
been heavy rain since you last sprayed.


Regards,
Nick Maclaren.

What makes you think that the white deposits on the tomatoes are in fact copper
sulphate?
Last I heard was that copper sulphate crystals were blue!
Regards,
Chris in Somerset

"Nick Maclaren" wrote in message
...
|
| In article ,
| Pam Moore writes:
| | I have just picked my first tomatoes for 5 years, having lost all to
| | blight for the last 4 years.
| | This year for the first time I have used Bordeaux Mixture which is
| | suggested as the nearest organic control.
| | Now I am concerned about the white copper sulphate deposits on the
| | fruit.
| | Is copper sulphate toxic?
|
| Yes, but not catastrophically so. You need micrograms of copper
| a day, the odd few milligrams on occasional will almost certainly
| do no harm, and the lowest lethal dose recorded is of the order
| of a gram.
|
| | Does anyone know how thoroughly I need to wash them?
|
| Moderately. No need to panic, but do wash them.
|
| | Has anyone else used BM? Advice is to spray weekly.
|
| Yes, on potatoes, where the problem doesn't arise. Weekly seems
| a bit excessive, but the issue for tomatoes is whether there has
| been heavy rain since you last sprayed.
|
|
| Regards,
| Nick Maclaren.

In article ,
"CK" writes:
| What makes you think that the white deposits on the tomatoes are in fact copper
| sulphate?
| Last I heard was that copper sulphate crystals were blue!

Bordeaux mixture is not just copper sulphate, and looks whitish
when the spray dries.


Regards,
Nick Maclaren.

On Wed, 13 Aug 2003 11:57:02 +0100, "CK"
wrote:

What makes you think that the white deposits on the tomatoes are in fact copper
sulphate?
Last I heard was that copper sulphate crystals were blue!

It says "Bordeaux mixture" on the pack.
It says it contains copper sulphate BUT the powder inside and the
deposit left on the plants is white. I also thought it would be blue.
Perhaps someone can explain!

Pam in Bristol

It says "Bordeaux mixture" on the pack.
It says it contains copper sulphate BUT the powder inside and the
deposit left on the plants is white. I also thought it would be blue.
Perhaps someone can explain!

I vaguely recall my first ever chemistry lesson at secondary school...

"Copper sulphate crystals were placed in a test tube and heated over a
bunsen flame. A crackling sound was heard and steam was seen escaping.
A white substance remained in the test tube."

The white stuff was "anhydrous copper sulphate", i.e. with all the water
removed...

On Wed, 13 Aug 2003 15:53:06 +0100, "Smeckler"
wrote:


The white stuff was "anhydrous copper sulphate", i.e. with all the water
removed...

maybe, but as you observe, it needs a lot of heat to produce and
absorbs water from the air very quickly (turning blue again). BM is
made from a mixture of copper sulphate and slaked lime. It's the
slaked lime that leaves the white deposit long after the CuSO4 has
dissolved/been washed off.
--
Derek Turner

Outlook Express is worth precisely what you paid for it.


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"Smeckler" wrote in message
It says "Bordeaux mixture" on the pack.
It says it contains copper sulphate BUT the powder inside and the
deposit left on the plants is white. I also thought it would be blue.
Perhaps someone can explain!

I vaguely recall my first ever chemistry lesson at secondary school...

"Copper sulphate crystals were placed in a test tube and heated over a
bunsen flame. A crackling sound was heard and steam was seen escaping.
A white substance remained in the test tube."

The white stuff was "anhydrous copper sulphate", i.e. with all the water
removed...

And, don't forget that BM is a copper sulphate and Lime mixture. I think the
last item might just have something to do with the white colour too.

Anyway, yes we have used it for some years to ensure our tomatoes do crop
but my understanding is that the disease, Tomato Blight, is brought by rain
and as we haven't had any for weeks (only two wet days this summer!) we
haven't bothered spraying yet this year. Will spray before we are due any
though.
Just wash the fruit thoroughly, the chemicals don't enter the fruit, and
they will be OK to use. Skin them if you are paranoid. :-)

We are trying some French variety called "Ferline" that is resistant to
blight (from the "Kitchen Garden" mag) so I won't spray those just to see if
they are indeed resistant. Will let you all know.

--
Bob

www.pooleygreengrowers.org.uk/ about an Allotment site in
Runnymede fighting for it's existence.

Thanks Nick and Smeckler for advice and info.


Pam in Bristol

"Pam Moore" wrote in message
...
I have just picked my first tomatoes for 5 years, having lost all to
blight for the last 4 years.
This year for the first time I have used Bordeaux Mixture which is
suggested as the nearest organic control.

There is no constituent in Bordeaux mixture which is organic. Its two
components, copper sulphate and calcium hydroxide, are both quite strictly
*inorganic*.

Now I am concerned about the white copper sulphate deposits on the
fruit.
Is copper sulphate toxic?

I think that copper sulphate is indeed toxic, but I may be wrong. I think
it gives you the squitters. However, the amount you are likely to get from
one tomato is probably OK

Does anyone know how thoroughly I need to wash them?

Reasonably well.

Has anyone else used BM? Advice is to spray weekly.

[Franz Heymann]

"CK" wrote in message
...


"Nick Maclaren" wrote in message
...
|
| In article ,
| Pam Moore writes:
| | I have just picked my first tomatoes for 5 years, having lost all to
| | blight for the last 4 years.
| | This year for the first time I have used Bordeaux Mixture which is
| | suggested as the nearest organic control.
| | Now I am concerned about the white copper sulphate deposits on the
| | fruit.

What makes you think that the white deposits on the tomatoes are in fact
copper
sulphate?
Last I heard was that copper sulphate crystals were blue!

In the extremely thin, powdery, layer on the coloured background of the
tomato, the blue might well not show up. In any case, the Bordeaux mixture
has calcium hydroxide (white) as well.

I put your post more or less where it belongs in the thread. Please don't
top post. It messes up the logical flow of the thread.

| | Is copper sulphate toxic?
|
| Yes, but not catastrophically so. You need micrograms of copper
| a day, the odd few milligrams on occasional will almost certainly
| do no harm, and the lowest lethal dose recorded is of the order
| of a gram.
|
| | Does anyone know how thoroughly I need to wash them?
|
| Moderately. No need to panic, but do wash them.
|
| | Has anyone else used BM? Advice is to spray weekly.
|
| Yes, on potatoes, where the problem doesn't arise. Weekly seems
| a bit excessive, but the issue for tomatoes is whether there has
| been heavy rain since you last sprayed.

[Franz Heymann]

"Pam Moore" wrote in message
...
On Wed, 13 Aug 2003 11:57:02 +0100, "CK"
wrote:

What makes you think that the white deposits on the tomatoes are in fact
copper
sulphate?
Last I heard was that copper sulphate crystals were blue!

It says "Bordeaux mixture" on the pack.
It says it contains copper sulphate BUT the powder inside and the
deposit left on the plants is white. I also thought it would be blue.
Perhaps someone can explain!

When copper sulphate is very finely powdered, it loses nuch of its blue
colour. And, there is white calcium hydroxide in the mix as well.

[Franz Heymann]

"Smeckler" wrote in message
...
It says "Bordeaux mixture" on the pack.
It says it contains copper sulphate BUT the powder inside and the
deposit left on the plants is white. I also thought it would be blue.
Perhaps someone can explain!

I vaguely recall my first ever chemistry lesson at secondary school...

"Copper sulphate crystals were placed in a test tube and heated over a
bunsen flame. A crackling sound was heard and steam was seen escaping.
A white substance remained in the test tube."

The white stuff was "anhydrous copper sulphate", i.e. with all the water
removed...

Unless my memory is letting me down, the anhydrous copper sulphate is
hygroscopic and absorbs its water of crystallisation from moisture in the
air, thus re-acquiring its colour.

[Franz Heymann]

On Wed, 13 Aug 2003 19:18:08 +0000 (UTC), "Franz Heymann"
wrote:


"Pam Moore" wrote in message
.. .
I have just picked my first tomatoes for 5 years, having lost all to
blight for the last 4 years.
This year for the first time I have used Bordeaux Mixture which is
suggested as the nearest organic control.

There is no constituent in Bordeaux mixture which is organic. Its two
components, copper sulphate and calcium hydroxide, are both quite strictly
*inorganic*.

Now I am concerned about the white copper sulphate deposits on the
fruit.
Is copper sulphate toxic?

see http://www.cleartech.ca/inside/msds/cupm-05-05-2003.pdf
--
Martin

On Wed, 13 Aug 2003 19:18:10 +0000 (UTC), "Franz Heymann"
wrote:

Unless my memory is letting me down, the anhydrous copper sulphate is
hygroscopic and absorbs its water of crystallisation from moisture in the
air, thus re-acquiring its colour.

Ah the joys of O level chemistry :-)
--
Martin