Mechanism and prevention of black spot disease in bagged apple

Apple bagging can significantly reduce the pests and diseases, improve fruit coloration, improve fruit surface finish and appearance quality, and is one of the important techniques to improve the economic benefits of apples. Therefore, most apple producing areas have adopted this measure in recent years. The expected effect is achieved. However, it has been found that the fruit surface after bagging is prone to black spot disease, which seriously affects the delicate appearance of the apple. Through the experimental research of fruit tree science and technology workers and fruit farmers, the mechanism and prevention methods of black spot disease have been clarified.

Symptoms Black spots, whether it is a bag or a film bag of apples will occur, not bagging generally does not occur. At the beginning of the disease, a small black spot with a large needle tip appeared around the fruit stalk, gradually expanding to the sesame and even the mung bean. However, it only occurs on the surface of the peel, does not penetrate into the flesh, tastes no bitter taste, does not cause festering of the flesh, does not spread and spread during the late growth period and storage period, has no effect on the internal quality, but has a great influence on the appearance quality and the selling price.

Mechanism The pathogen of black spot disease is Trichophyton rubrum, which is a weak parasite in the subgenus. It began to occur in late June, and the midsummer rainy season from early July to early August is the peak period, and is rarely found after late August. Orchards with low topography, poor ventilation and light transmission, canopy closure, frequent rainfall, high temperature and high humidity, strong tree growth and high nitrogen fertilizer have many serious diseases. The reason why bagging fruit is prone to this disease is that the fruit is poorly breathable in the bag, the temperature is high, the humidity is high, especially after the rain, the water is accumulated in the bag, the paper bag is not dry after being wet, and even stuck on the fruit surface and aggravated Humidity and poor ventilation will increase the incidence. The bagged fruit is not affected by these microclimate environments in the bag, and the ventilation and light transmission are good, and the heat dissipation is fast, so the weak parasitic bacteria are difficult to infect.

Prevention and treatment methods 1 spray prevention. After Xiehua, before bagging, spray 80% of mancozeb powder 800 times or 40% DuPont Fuxing 8000 times solution every 10 days, and spray 2~3 times for sterilization prevention.

2 use high quality fruit bags. The quality of the fruit bag is not only directly related to the bagging effect, but also has a great relationship with the severity of the disease. Therefore, the outer paper bag must use wood pulp paper made from coniferous wood raw materials, and the paper thickness should be moderate, soft and tough, good air permeability, strong shading, no water seepage, can withstand wind and sun, rain, edge glue Strict; the inner bag should not fade, the wax is good and the wax is even, it is resistant to water and does not dissolve under high temperature and sun. At present, the "Kobayashi" bag made in Japan, the "Jiatian" bag made in Taiwan, and the "Kaixiang" bag made in China are the best. The film bag is pressed with the original polyethylene plastic film (retirement film is avoided), the red film is used in the area with poor illumination, Yunnan is the plateau, and the ultraviolet light is strong. It is suitable to use the translucent milky white film bag which is not easy to cause sunburn.

3 bagging early. According to local experiments, early bagging can make young fruit less affected by sunburn and adverse weather outside the environment, and adapt to the bag environment early, get more exercise and enhance the resistance to stress. The film bag should be 15 to 20 days after the flowering, and the paper bag should be 25 to 35 days. If the film bag is filled with paper bags, the paper bag should be placed 15 to 25 days after the film bag. When bagging, the fruit bag should be bulged, the upper seal is tight, the bottom is transparent, no wrinkles, no fruit, and the fruit is suspended in the center of the bag.

4 Improve light, fertilizer and water management. Do a good job of pruning, especially to make the summer shears thin and thin, make the leaf layer thick and suitable, improve ventilation and light transmission; reduce and control nitrogen fertilizer from the middle of the growth period, avoid NPK imbalance and increase calcium deficiency and boron deficiency Drainage during the rainy season to reduce soil moisture and air humidity.

5 Check after the rain. Every time after the next heavy rain, it is necessary to check in time. If the drainage hole is found to have accumulated water in the small bag, the large drainage hole should be cut to eliminate the accumulated water and facilitate the ventilation; the bag that is smashed by the rain and glued on the fruit surface should be removed in time. Clean and a new set of bags.

Two diseases that are easily confused with black spot disease

In the bagging apple orchard, if the experience is insufficient, the black spots appearing in the following two diseases will be mistaken for black spot disease, which will prevent the disease from being ineffective and ineffective.

(1) The black spots are distributed in the upper part of the sputum, around the top of the fruit, and in the crotch. When they occur, they become larger spots, which only occur on the peel, not deep and flesh, and do not cause fruit to rot. This disease is lacking. Calcium-induced acne spot disease can cause bitter bean disease in severe cases. It is significantly different from black spot disease: first, black spot disease is mostly bagged fruit, non-bag fruit does not generally occur, and acne spot disease occurs both in bagging and non-bagging; second, black spot The flesh under the disease point has no bitter taste, while the flesh under the plaque spot has bitter taste; the third is that the spot of black spot disease does not expand in the late growth stage and storage period, and the lesion of acne spot disease will expand and Lower depression. The prevention and treatment method is to apply 80-100 g of calcium nitrate or calcium oxide and calcium sulfate per plant in the autumn base fertilizer. From the germination of new leaves to August, spray 300-400 times of calcium nitrate or dihydrogen phosphate every other month. Calcium, or 800 times amino acid calcium, is supplemented with calcium.

(B) There are light brown spots, which are irregularly distributed on the fruit surface. It differs from black spot disease: first, both bagged fruit and non-bag fruit occur; second, the disease spot of black spot disease is small and does not fester, and after its lesion is enlarged, the diseased part festers and even causes the whole Fruit rots. This is a round rotten fruit disease. The control method is the same as the ring disease that harms the branches.
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