Preparation and Application Methods of Bordeaux Mixture in Pear Orchards

    As a mineral-source pesticide, Bordeaux mixture is a fungicide advocated for use in green fruit production, and it has a very good control effect on pear ring rot and pear black spot and pear scab. However, many fruit growers make improper operations during preparation and application, resulting in reduced efficacy and even phytotoxicity. The methods for how to use Bordeaux mixture in pear orchards are introduced as follows:

Pear

   (1) Preparation ratio. The optimal ratio of copper sulfate, quicklime and water for Bordeaux mixture used in pear orchards is 1:4:2000, but the amount of lime can be appropriately increased to improve the adhesion of the spray solution. Each spraying can last 30 to 40 days, and only 3 to 4 sprayings are needed during the entire growth period of the pear trees in the pear orchard (April to September), which will not have an adverse effect on the appearance of the pears and will not produce fruit russeting. In contrast, with the traditional 1:2:200 Bordeaux mixture, each spraying can only last 15 to 20 days, and it easily produces fruit russeting. If the amount of lime is excessive, with a ratio of 1:6:200 Bordeaux mixture, it will affect the photosynthesis of pear tree leaves and also reduce the efficacy.

   (2) Preparation method. Metal containers should not be used to prepare Bordeaux mixture, but wooden barrels, plastic barrels or porcelain containers can be used. For lime, white, lightweight, lumpy fresh lime should be selected; lime that has been stored for a long time and has already powdered and become soft cannot be used. When preparing, first use 2/3 of the water to dilute the copper sulfate and stir it thoroughly to dissolve it, then use 1/3 of the water to prepare the quicklime into a thick lime milk, and then slowly pour the relatively dilute copper sulfate solution into the thick lime milk while stirring, thus preparing a sky-blue colloidal suspension Bordeaux mixture without precipitation.

   (3) Application method. As a protective fungicide, Bordeaux mixture should be used before pear trees develop the disease, and spraying should be careful and uniform; spray the Chengdu pear leaves until they drip, and use a drenching method for the branches and trunk. For adult pear trees, about 150 kg of pesticide should be used per mu of pear orchard each time. The spraying time should be from 9 a.m. to 4 p.m. on sunny days; it should not be used on cloudy days or when there is dew, and in rainy seasons it is suitable to use before rain. In southern regions, the first use of Bordeaux mixture on pear trees should be 10 days after flowering, that is, as early as mid-April. As an alkaline pesticide, Bordeaux mixture should be used immediately after preparation, and generally cannot be mixed with other insecticides and fungicides to avoid phytotoxicity; moreover, the time of using other insecticides and fungicides should be staggered from Bordeaux mixture by 7 to 10 days, otherwise the efficacy will be reduced. However, it is worth noting that Bordeaux mixture can be mixed with Tuzet and can improve the efficacy. But if Bordeaux mixture is used in pear orchards for a long time, there will be a trend of increased damage by red spiders, so from May to July, before using Bordeaux mixture, the whole orchard should first be sprayed once with 73% propargite 1800 times, or 20% dicofol 800 times.