The cultivation of fruit trees in greenhouses is in a semi-closed state, with less gas exchange inside and outside the shed, and fruit trees are often victimized by harmful gases during the production process. Therefore, in the production process, we must carefully identify, correct diagnosis and timely prevention.

First, the source of harmful gases Greenhouse fruit trees in the production process of common harmful gases are ammonia, nitrogen dioxide, sulfur dioxide, diisobutyl phthalate, ethylene and chlorine and so on.

1. Ammonia. Mainly from manure, especially the application of unfermented organic fertilizer or ammonium bicarbonate, urea and other nitrogen fertilizers, when the greenhouse temperature is high, the most likely ammonia. It usually occurs in 3-4 days after fertilization. When the ammonia concentration in the greenhouse reaches 5 μl/l, fruit trees can be affected.

2. Nitrogen dioxide gas. Mainly from excessive application of ammonium nitrate and other nitrate nitrogen fertilizer. It usually occurs 10-15 days after fertilization. When the nitrogen dioxide concentration reaches 2-3 μl/l, the fruit trees can be affected.

3. Sulphur dioxide gas. Mainly from sulphur fumigation and heating coal. The incomplete emission of sulphur fumigation gas, or the incomplete combustion of coal, or the unobstructed flow of the flue gas, and the high sulphur content in the coal, can all cause excessive levels of sulphur dioxide gas. When the sulfur dioxide gas exceeds 5 μl/l, fruit trees can be damaged.

4. Diisobutyl phthalate, ethylene and chlorine. Mainly from poor quality plastic film or other plastic products. When the content of diisobutyl phthalate reaches 10-20 μl/l in the shed water droplets, and the ethylene and chlorine concentration reaches 0.1 μl/l, it will cause damage to fruit trees.

Second, harmful gas hazards

1. Ammonia. It mainly damages the leaves of fruit trees and appears water stain spots. The leaf margins are charred and curled to the inside. In particular, the victims suffered from a heavy heart, and the heart and the leaves showed chlorosis between the veins and caused the following 2-3 leaves to fade in the heart; the leaf margins were charred. Distribution in the shed: more incidence of the whole shed, shed and lighter than the middle.

2. Nitrogen dioxide gas. The main damage to the leaves, the occurrence of irregular green spots, the diseased tissue diseased leaves clear boundaries. In severe cases, some or all of the leaf flesh will die with the exception of leaf veins.

3. Sulphur dioxide gas. The main damage to the new leaves, water spots at the diseased spots, and finally into a white, diseased and healthy parts of the point or block necrotic spots.

4. Diisobutyl phthalate gas. Leaves of the victim's veins retreated green and turned white. The growth of the leaves was obstructed. The affected parts were mainly young leaves and the tip tissues.

5. Ethylene gas. After injury, the leaves began to show sagging, bending, and then turn green and white, and the plants died when severe.

6. Chlorine. After the victim suffers, the leaves turn green and turn yellow, and then turn white. In severe cases, the plants die.

Third, the simple determination of harmful gases

1. Detect the pH of the shed film water droplets. There is no harmful gas in the test shed, and the pH of the shed can be measured by using a pH test paper (sold in the market) immediately after the decantation in the morning. Under normal conditions, the shed film droplets should be neutral to slightly alkaline with a pH between 7 and 7.2. When the pH value reaches 7.5 or above, ammonia gas is generated and accumulated in the shed. When the pH is below 6.5, gas such as nitrogen dioxide is produced in the shed.

2. I taste the taste of drops. Use the tip of the tongue to taste the water droplets on the roof. There is a slippery sensation of excessive ammonia, and an astringent taste is an excess of nitrogen dioxide gas.

Fourth, gas prevention and control measures

1. Reasonable fertilization. Greenhouses should be dominated by organic fertilizers, supplemented by chemical fertilizers. Organic fertilizers should be fully cooked before application. Nitrogen fertilizers should be applied in small amounts for several times. Do not use ammonium bicarbonate.

2. Timely ventilation. Use the time when the temperature is high before and after noon to open the vents to exchange gas inside and outside. Special attention should be paid to a few days after the rain and snow conditions and top dressing are applied, as far as possible to ensure the temperature requirements of fruit trees, as much ventilation and ventilation as possible.

3. Select high-quality film and plastic film. Avoid using products that incorporate more plasticizers.

4. Pay attention to smoke. When warming up with fire, attention should be paid to installing smoke exhaust facilities such as smoke windows or flue gas ducts.

5. Strengthen management. Reasonable watering, timely scratching, good regulation and control of the temperature and humidity suitable for the growth of fruit trees, promote the development of fruit tree roots, ensure robust growth of fruit trees, improve resistance to harmful gases.

6. Remedial measures. When fruit trees are harmed by harmful gases, the cause of the damage should be determined and management should be strengthened in a timely manner. In the case of ammonia hazards, the leaves can be sprayed with 1% vinegar; in the presence of sulfur dioxide gas, the leaves can be sprayed with a stone sloping agent to promote the recovery of the leaves as soon as possible.

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