A solution of copper sulfate
In a five-liter bucket, we will prepare a solution of copper sulfate CuSO₄ · 5H₂O. Pour 2 liters of hot water (about +50°C) water, pour out the powder and stir thoroughly until completely dissolved. Then, gradually and stirring, add up to 5 liters of cold water. Now, if you have litmus tests and a desire, you can check the pH of the obtained solutions. Lime milk will give an alkaline reaction, and a solution of copper sulfate will give an acidic one.
It’s time to combine both parts and get the Bordeaux liquid. In a bucket with lime milk, pour a solution of copper sulfate in a thin stream with constant stirring.
- Do not confuse it: we add copper sulfate to lime milk, not vice versa!
We get 10 liters of Myosotis-colored liquid containing Cu(OH)₂, CuSО₄ и CaSО₄. Now let’s approach the process from a scientific point of view. The Bordeaux liquid should become neutral: the lime alkali neutralizes the vitriol acid. We use indicator strips or a device for measuring acidity — the pH value should be 7-7.2.
If there are no special devices, we take out a nail. If necessary, we pre-clean the rust. We lower the nail into the resulting liquid. If after some (short) time a copper plaque has formed on the metal surface, it means that the resulting suspension has an acidic reaction. This is a very important point. Using an acidic solution can burn the leaves. This is where a prudently prepared jar with additional lime milk will be required: if necessary, we increase the concentration of alkali in the solution (add lime milk), stirring — and controlling the reaction.
How to use Bordeaux liquid correctly
Bordeaux liquid can be prepared in different concentrations, depending on the purpose.
Before the leaves bloom and in the fall, a 2-3% solution is used. For the preparation of 10 liters take:
- 200-300 g of copper sulfate,
- 300-450 g of quicklime or 250-400 g of fluff.
In summer (during the growing season), the concentration of the solution should be less than 0.5-1%. To prepare 10 liters, you will need:
- 50-100 g of copper sulfate,
- 100-150 g of quicklime or 75-100 g of fluff.
The finished Bordeaux liquid is allowed to settle for 1-3 hours. Then we pour it into the spray container, having previously filtered it through a gauze folded in four, or a fine sieve, so that the insoluble particles do not clog the nozzle.
The finer the water “dust” your sprayer gives out, the more effective and safe the treatment with Bordeaux liquid is for plants — do not allow large droplets to accumulate on the leaves and the liquid to drain to the soil surface. Large drops can be phytotoxic to plants, especially if you carry out treatment during the growing season (for example, spray tomatoes). The ingress of the solution to the soil contributes to the accumulation of copper in it. An overdose can cause depression of plants, and regular treatment with drugs containing copper — and its accumulation in vegetables.
- Bordeaux liquid should not be combined with other drugs (insecticides, top dressing), since the alkaline environment of the solution can neutralize their effect.
- Bordeaux liquid is an unstable remedy, it can not be prepared for the future. Dilute immediately before use. In extreme cases, the finished solution can be stored for no more than a day, and then it is worth adding 1 tablespoon of sugar to 10 liters.
Bordeaux liquid is an inexpensive and effective remedy. The duration of the fungicide is up to four weeks. And its regular preventive use will allow you to forget about fungal diseases of plants.