Topic: Rhubarb spray

[vinotinto]

I've boiled up some rhubab leaves as a spray for the allotment, but a couple of questions....is it safe for use on vegetables?  We have brocolli growing with some aphids which I was going to spray but if its not safe...
Also most recipes say use in 24 hrs.  Any reason why it cant be stored for longer?
Thanks!

[Chrispy]

I have no idea how toxic it is, but it is a lot more toxic than anything you will get at the garden centre, so I would not use it on anything you would want to eat.

[Robert_Brenchley]

Oxalic acid, which is the poison involved, is toxic in quantity, but it's also found naturally in some of the veg we eat regularly. It's very soluble in water, so if you wash the veg, or they get rained on a couple of times, it'll be gone.

[Melbourne12]

I've boiled up some rhubab leaves as a spray for the allotment, but a couple of questions....is it safe for use on vegetables?  We have brocolli growing with some aphids which I was going to spray but if its not safe...
Also most recipes say use in 24 hrs.  Any reason why it cant be stored for longer?
Thanks!

In anything other than laboratory conditions, it degrades naturally within 24 hours.  Plus, as Robert Brenchley says, it's soluble and will simply wash off.

Even if you made quite a strong solution, say by chopping up 5 kg of rhubarb leaves in 5 litres of water and crushing and pulping the leaves, then straining the liquor, I very much doubt you'd get better than a 0.2% solution (0.5% acid in leaves by weight, and assuming 40% extraction).

The greatest danger from oxalic acid is to your eyes (and lungs if you breathe the vapour).  But that's such a weak solution that I doubt it would do any harm even if you chugged it neat (actually I've just looked up the toxicity and even a small-framed adult would need to drink at least three gallons of rhubarb leaf tea to run any risk of fatal poisoning).

[vinotinto]

Thanks all appreciate the answers!