Measuring copper fungicide properly

[bencuri]

I would like to use copper hidroxide to spray tomatoes to prevent blight. My problem is that the guide on the box is confusing. It says that the dilution should be 20g copper / 10L. But there is also another instruction: the amount sprayed one time should not be more than 1kg / hectare. My garden is 10m2, that means to this place the maximum one time copper amount should be no more than 1g. If I summerize this, it means one time I can spray 0.5L, that will have 1g copper, this way meets the dilution and the soil stress guidelines at the same time on 10m2. But the problem is: spraying 0.5L only on my plants is impossible. I have tomato plants grown high, spraying them all with this small amount is nonsense, my spray equipment cannot do that. I need at least 4-5L liquid to spray it comfortably. I asked the shopkeeper what if I dilute only 1g in 5L. Then I can spray well and maintain the soil stress instructions. But he said this way the dilution is too thin, and won't have effect. I wonder why not however, when it will be 1g copper either way, it is just the amount of water sprayed on 1 plant that varies, not the diluted copper. He suggested to stick to the dilution instructions first of all. But that way I need to spray out much more gramms of copper (5g on 10m2) than the allowed soil stress level.

The problem is, maybe if I had a sprayer that can spray out the liquid as fog, 0.5L would be enough, but at the moment I don't have access to such things. The recent sprayer I have sprays fine when set to medium strength, that wets the leaves instead of spraying out a thin film of fog. Setting to minimum it is sprinkling much bigger drops than fog in tiny amounts, it is useless at that setting, the wetting is very uneven.

What do you think I should do in this case?

 

[YumYum]

Copper builds up in the environment so that is why there is a reccomended limit. Not sure what the actual recommendations are here.

Copper hydroxide is 65.13% copper so if you want 20 g of copper, you use 30.71 g of copper hydroxide (math = 20g / 0.6513).

If the max amount of copper, not copper hydroxide, is 1 kg per hectare, and 10 square meters equals 0.001 hectare, that does equal a max of 1 grams of copper per 10m2, which is 1.54 g of copper hydroxide per 10m2. That still doesn't amount to much but it does mean you can use 0.77L of spray.

I've used a copper sulfate spray a handful of times so I don't really know much about the effectiveness of it but I don't think I would dilute it below what it says. You want enough copper to sit on the leaves so a fog machine is a bit of a stretch if you ask me. Just spray enough to wet the leaves evenly without runoff is about all you can do.

 

[YumYum]

Looking at a Bonide copper products label it has different recommendations for different vegetables / fruits and it recommends a maximum amount of copper per year, not each spraying so you may want to take that into account also. If I done the math right that is a max of 6 kg - 19 kg of copper per hectare per year.