There are many black spots on the apple tree. What fertilizer should we use?

The climate this year is quite abnormal. Some time ago, many fruit farmers reacted, and there were many spots on the fruit surface after picking bags. The picture below shows the symptoms of black spot disease sent to me by fruit farmers in Jingning area of Pingliang, northwest China. Taking this question as an opportunity, I would like to answer and share the preventive measures against similar black spot disease of apples this year.

This kind of spot disease like the above picture is called lenticella spot disease, and of course there are other fruit surface spot diseases, such as bitter pox spot disease, ring spot disease, leaf spot disease, anthracnose and so on. However, this year's spot disease is mainly lenticella, and deciduous disease basically does not occur. Bitter pox and ring rot can also be excluded from fruit surface performance. Fruit farmers can judge according to the incidence of their orchards.

Symptoms of freckled spot disease

Dermatosis is erythema centered on stomata, which mostly occurs at the hips and tops of fruits. The diameter is about 2~4㎜, and the color is dark. The central stomata of some red spots are necrotic and black, and the spots do not expand and rot for a long time after fruit picking.

The disease of lenticels began to occur about 3~4 days after the bag was removed, and it developed rapidly and was in a very concentrated period. This spot disease is more serious in dry land, sloping land and weak trees in sparse gardens, and most fruits occur in large numbers 4~5 days after bag removal.

Causes of stomatal spot disease

Dermatosis is a physiological disease caused by many factors.

1, climatic factors

Since the beginning of spring this year, successive months of drought have caused water imbalance in fruit trees. The pathogenesis is the lack of irrigation in the orchard in arid and thin land. In dry weather, the water supply in fruits is often seriously insufficient. Many fruits will form tiny cracks at the stomata after encountering sudden rainfall or irrigation. These tiny cracks are imperceptible to the naked eye when the bag is removed, but 3~4 days after the bag is removed, a blush will be formed around the broken lenticels, resulting in red and black spots.

2. Pesticide factors

At ordinary times, when fruit farmers spray pesticides on fruit trees, this spot disease will also occur because the pesticide concentration is too high or the pesticides that are irritating to fruits are sprayed, especially because the quality of bagged paper bags is poor or the pathogen protection is not in place. Because the skin of the fruit just taken out of the bag is tender, the protective tissues such as cuticle, waxy layer and lenticels are weak, and it is very sensitive to chemicals.

It is suggested that the fruit bags should be exposed for 48 hours before using low-irritant biological pesticides.

Control methods of apple lenticels spot disease

For the prevention and treatment of lenticels, prevention is mainly carried out from the following aspects.

Strengthen water and fertilizer management: water in time in case of drought. If there are no irrigation conditions, measures such as storing fertilizer water in caves (water and fertilizer in caves, drip irrigation, etc.) shall be taken. ), covering with plastic film and planting grass to improve soil moisture status; At the same time, in case of waterlogging, water should be drained in time to avoid uneven growth of pulp and peel. Pay attention to calcium supplementation: pay attention to the application of trace elements such as calcium supplementation, improve fruit hardness, improve peel toughness, and avoid small cracks. If calcium is supplemented, it is necessary to popularize the main absorption peak of calcium here. After flowering, before and after fruit bagging, there is also a late stage of maturity. These are the answers to the common freckles this year. In short, everyone should have a scientific understanding of the occurrence of apple diseases and insect pests, so as to prevent them in advance and reduce the occurrence of diseases.