Correct methods for using non-systemic fungicides
How are non-systemic fungicides used? Please give an introduction. The following introduces how to use the non-systemic fungicide Bordeaux mixture: Bordeaux mixture is a sky-blue viscous suspension made from copper sulfate, quicklime and water. It is alkaline and corrosive to metals. It is a non-systemic protective inorganic fungicide, ...
How are non-systemic fungicides used? Please give an introduction
The following introduces how to use the non-systemic fungicide Bordeaux mixture:
Bordeaux mixture is a sky-blue viscous suspension made from copper sulfate, quicklime and water. It is alkaline and corrosive to metals. It is a non-systemic protective inorganic fungicide, and its active ingredient is basic copper sulfate. After crops are sprayed, it adheres in particulate form to the crop surface and the surface of the pathogens. Through the action of factors such as air, moisture, carbon dioxide and secretions from crops and pathogens, it slowly converts into soluble copper and thus exerts its fungicidal effect. Bordeaux mixture precipitates after standing for a long time and produces crystals that gradually reduce its efficacy, so it must be prepared and used immediately and cannot be stored. Bordeaux mixture can control many diseases of cotton, peanut, rapeseed, broad bean, vegetables and fruit trees. Because of its good adhesion, it is not easily washed off plants by rain, and it is simple to prepare and low in cost, so it is deeply welcomed by farmers, but improper preparation and use can produce the opposite effect.
1. Material selection
The quality of Bordeaux mixture depends not only on the preparation method but also closely on the quality of the raw materials. Commercially available copper sulfate varies little in quality, while quicklime varies greatly. You should choose fully burned lime lumps that are free of impurities and low in density. Powdered lime that has absorbed moisture or weathered is generally not used. If there is no quicklime and hydrated lime must be used instead, the amount should be increased by 30-50%. The water should be river, lake, pond or ditch water. High temperatures will cause the colloidal particles of Bordeaux mixture to coagulate and precipitate, and when preparing it, hot water and water with a relatively high chloride content should also not be used, to prevent phytotoxicity.
2. Preparation
The preparation method generally adopts the "two-liquid method". That is, copper sulfate and quicklime are each dissolved in half the amount of water in two containers, then the copper sulfate and quicklime are simultaneously poured into a third container, and a wooden stick is used to continuously stir gently in one direction until the liquid turns sky blue. Alternatively, 90% of the water can be used to dissolve the copper sulfate and 10% of the water to mix the lime milk, then the copper sulfate is slowly poured into the lime milk until it turns sky blue. Bordeaux mixture prepared by these 2 methods has good suspension performance, fine particles, is not easy to precipitate, has strong adhesion on crops and has a good disease-control effect. Lime milk must absolutely not be poured into copper sulfate, otherwise the colloidal particles of the Bordeaux mixture will become coarser and it will precipitate easily. In addition, metal containers must not be used to prepare Bordeaux mixture; porcelain vats, wooden barrels or plastic buckets should be used, and used sprayers must also be rinsed clean immediately.
The ingredient proportions for the various formulations of Bordeaux mixture should be determined according to the sensitivity of the crop to copper sulfate and quicklime, as well as which disease is being controlled, the season and the temperature. In general, the more lime used, the safer it is for plants and the longer the effect lasts, but the slower the fungicidal action. If less lime is used, the fungicidal action is faster, but phytotoxicity is more likely, so it can only be used on crops with relatively strong copper tolerance.
There are several mixing ratios for preparing Bordeaux mixture, and which one to use should be determined according to the crop and the type of disease. Generally there are several types such as the "equal-amount formula", "half-amount formula" and "double-amount formula".
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