the reason
The black spot disease caused by apple is Trichoderma virens and Cephalosporium acremonium. The black spots caused by Trichoderma rosacea are concentrated in the shoulders of the iliac crest and palate, the lesions are about 1-3 mm, and the surrounding area is black. The center of the lesions is leucorrhea flow; the black spots caused by Cephalosporium acremonium More concentrated in the fruit surface or fruit shoulder, lesions larger, about 3-5 mm, brown or black than the size of round spots, round spots slightly sunken, individual darker, light red or green halo around the lesion is Its salient features. These two black spot diseases affect the commercial nature of the fruit, but generally do not expand during storage and cause rotten fruit.
It is Alternaria spp. that causes apple red spot disease. Symptoms usually show up within a few days after the bag is removed, and red dots can spread over the whole fruit. Symptoms are irregular red or purple spots centered on the lenticels. The lesions are generally not large and do not penetrate deeply into the flesh, and will not cause rotten fruit during storage.
The pathogens causing apple black spot and red spot disease are all belong to weak parasites. In the case of not being bagged, it will not happen because the environment is not suitable for its survival. In the case of bagging, if the drug is not used in time after flowering until bagging or improper drug selection or improper fruit bag (mainly because the number of vent holes is small or small or the number of inner membrane vent holes in the film plus paper bag is small), After the upper bag is bagged, the temperature inside the bag is high and the humidity is high, thus creating favorable conditions for the occurrence and development of these bacteria.
Prevention
1 rational use of drugs. The period from flowering to bagging is the key period of drug use throughout the year, and it is the major damage period including various diseases such as black spots and red dot disease, and it is also a highly sensitive period for fruits. In drug selection, it is necessary to consider effective, but also consider no damage to the fruit surface. Propylene zinc, polyoxin, difenoconazole, thiophanate-methyl, pyrimethanil and other drugs are very effective in improving the smoothness of the fruit surface and preventing the occurrence of black spots and red dot disease.
In addition, red dot disease also pay attention to medication after the bag. If the bag is removed from the bag after a long period of rain or if the bag is too late and the coloring time is too long, it often induces red spot disease. In this case, it must be sprayed with thiophanate-methyl or peracetic acid in time, which can be effectively controlled.
2 pay attention to medication methods. The first is to avoid the high temperature period and apply medication before 10 o'clock in the morning and after 4 o'clock in the afternoon. The second is that it is best not to use spray guns. When spraying, it is necessary to pay attention to every fruit sprayed, leaving no dead ends, but also pay attention to the spray head from the fruit surface not too close to avoid hitting the fruit surface.
3 choose a good fruit bag. When selecting fruit bags, you must choose high-quality double-layer paper bags and breathable high-quality paper plus film bags. In addition, after the bag is bought back, it is necessary to check the bottom of the bag before the bagging. If the ventilation hole is too small, it must be re-processed, then increase the ventilation hole and then bagging, and pay attention to the bag mouth tightly (to prevent water intake ), The fruit is vacant (to prevent burning on the day), and the vent opens (prevents black and red spots).
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