Cheshunt Compound Shelf Life ?

I was browsing the archives on the techniques for using the anti damping off fungicide , Cheshunt Compound , to my horror I read that it has a shelf life ! The tin I have is now 4 years old , should I chuck it before next season ? Can a chemical compound of copper sulphate go off ? I never excelled at chemistry :(

TIA

 

Hi Harry

I have always understood that it does have a shelf life. My chemistry was so long ago that I can't remember any of it. I can only presume that Cheshunt compound (copper sulphate and ammonium carbonate) works because it is an active chemical that acts on mould and kills it. But like any active chemical, over a period of time it will also react with oxygen and moisture in the air to produce a more stable and less active compound. The more stable product is now less inclined to react with mould.

I have always avoided buying the tins in case it all goes off, and bought instead the box with sachets. I assume that a sealed sachet will have a very long shelf life, but will start to deteriorate after opening.

If you have kept the tin sealed when not in use, it may last for quite a while. But even old Cheshunt compound (perhaps at a higher strength) will be better than nothing.

 

When copper sulphate absorbs water as it may well do in storage, it undergoes a chemical change.

CuSO4+H2O ---> CuO+H2SO4

Copper sulphate + water -->Copper oxide + dihydrogen sulphate (sulphuric acid!). The latter isn't the best thing to dip roots into :skp:

Ammonium carbonate (NH4)2CO3 (carbonic acid) when exposed to air (as it will during prologed strorage) changes to ammonium bicarbonate, which isn't what it started out as when packaged.

I hasten to add that I didn't pay enough enough attention during 'smelly chemy' lessons at school and gained a mere O level. The above info is a synopsis from some Googling.

 

It could well be something like that Dave - not nice. But I suspect there is some sort of ageing process as well in there, as you make up your solution of Cheshunt powder in water - so it must take some time.

I think the secret of anything like that is to keep the tin sealed when not in use. Moisture and air tend to make most things deteriorate over time.

 

Blast! I bought a big tin thinking it would see me out :(

I shall use it less frugally.

Yours, Scrooge ...

 

Thanks Peter and Dave for the advice on Cheshunt Compound - especially the chemical formula , DaveW ! But as always in gardening an answer always raises another question. Now I know this one is like how long is a piece of string .... but how long would a regularly sealed tin of Cheshunt last ? Mine is coming up for its 5th season - should I bin it ?
Peter - the packet solution you mentioned , I presume is "Murphy's Traditional Copper Fungicide" in 10 x 6gm sachets for about £6, making 4 litres per sachet. This may be a better option , but is it still avaailable ? It seems to be non-stocked on the sites I have seen . :cnfs:

 

Harry I recently looked for some as I have started to sow some seeds again. But I couldn't find any. I wonder if copper compounds have been banned. Most other things have. :D

 

Happened to read in RHS "The Garden" that Chesunt Compound is banned - use up by March 2011 I think? and replaced by something else that I have never heard of. I'll go dig out the article if anyone needs me to? A load of other things have "gone" too - "Rose Clear" for example.

 

Thanks Kristen. I did see a tin in a local garden centre, but was looking for the sachets. I will have to get what I can before they stop stocking it.

 

Bearing in mind that it will be illegal to use (rather than sell) it after March 2011 ... of course :thumb:

 

Cheshunt really does have a limited shelf life.

I recently bought a tin of what was clearly old stock, when I opened it. Rather than a fine mid blue powder, it consisted of dark blue crystals with an overpowering small. I made up a solution as directed, and tested the pH with a cheap, garden, pH meter. Dave - you were absolutely right. The pH was 1.5. ie it was virtually concentrated sulphuric acid. It would have killed anything it touched.

I tried unsuccesfully to increase the pH first with Sodium bicarbonate (the gentle way) and then with Sodium Hydroxide (Caustic Soda - the sledgehammer way). Both were failures.

But all my Googling has paid off. I found this on the Jungle Seed site under Other Gardening Equiptment. http://www.jungleseeds.co.uk/

Protective Fungicide including Damping Off in Seedlings 6 Sachets
Unfortunately Cheshunt Compound has now been withdrawn from sale because of EEC regulations. However this new Dithane alternative should do the trick for those difficult seedlings. Each sachet makes up 3 litre but we would thin out to 5 litre for a weak solution that could be used regularly on small seedlings until established. Sterilised compost is also a requirement for effective results. (Use your kitchen microwave on the compost, let it cool down and then use for seed sowing). This product can also be used to control blight etc on fruit crops.

So I think that is a better route to go down.

 

So, Peter, what is a "Dithane alternative".

Sounds like an old and well tried fungicide, (probably toxic), being replaced by a "new toxic" chemical.

 

Pete I had no idea. But you have prompted me to have a Google and I found that the active ingredient is Mancozeb. With some info here http://environmentalcommons.org/cetos/criticalhabitat/mancozeb.pdf

As you suggested it is an old and toxic fungicide replacing an old and toxic fungicide. But then if it kills mould it has to be toxic.