Please help me determine how much Copper Sulfate pentahydrate powder to add to water

[Winstonsmith314]

Hello! After a few decades, I'm growing orchids again, and I have a lovely Brassia, which unfortunately has fungal rot at the base of the largest pseudobulb at one end. As stated I have a finely powered CUSo4*5(H2O). How much powder should I use in say 1L to reach the effective concentration for my intended purpose? Thanks!

[rbarata]

What you want is a solution called "Bordeaux mixture".
It was widely used in my country, in wineyards but now its use is illegal due to environment damage.
I would use a fungicide instead: easier, safer, probably more effective but, before all that, I would investigate which cultural problem I might have that caused fungi to appear.

[Winstonsmith314]

Thank you for your response. I have identified the problem and corrected it, but the only thing I have handy is physan-20, and confess to being bewildered by the number of fungicides available. Do you have a suggestion? Again thank you.

[Ray]

Copper sulfate pentahydrate is 25.4% Cu.

Phyton 27 is 5.5% Cu.

That suggests that you to get an equivalent elemental copper dosage, you should choose the recommended Phyton 27 concentration and mix 5.5/25.4=0.2165 of that amount of copper sulfate.

If that’s 2-3 tsp/gal, then you’d be OK with 0.43-0.65 tsp/gal.

[Winstonsmith314]

Originally Posted by Ray

Copper sulfate pentahydrate is 25.4% Cu.

Phyton 27 is 5.5% Cu.

That suggests that you to get an equivalent elemental copper dosage, you should choose the recommended Phyton 27 concentration and mix 55/25.4=0.2165 of that amount of copper sulfate.

If that’s 2-3 tsp/gal, then you’d be OK with 0.43-0.65 tsp/gal.

Thank you, that's exactly what I needed.