Can Apples with Black Spots (Wisdom Fruit) Still Be Eaten? Causes and Treatment Methods
Apple black spot disease is a common disease during the growth period of apple trees. It causes apples to lose their commercial value and affects fruit growers' economic income, so fruit growers are very afraid of this disease occurring. So can apples with black spots still be eaten? What causes it? What medicine can cure it?
Can they be eaten once black spots appear?
Yes, they can be eaten, because according to current scientific research results, the weak parasitic fungus of the Deuteromycotina subdivision is harmless to the human body.
Causes:
The pathogen of black spot disease is one of the saprophytic fungi commonly found on various plant residues. Mummified flowers, mummified fruits, dead fruit spurs on apple trees, and fallen fruits and dead branches under the trees are all its overwintering sites.
The diseased and dead fungi spread through wind and rain, and begin infecting floral organ residues during the apple flowering period, including dried calyxes and styles, filaments, and anthers. In years with rain during the flowering period and many rainfall events from the flowering period to bagging, the rate of fungal carriage on floral organ residues is high.
After the fruit is bagged (especially with inner-black double-layer bags), the dark and humid environment inside the bag creates suitable conditions for the growth and reproduction of the pathogen. The fruit bag sways in the wind, and the pathogen spreads to the fruit surface, thereby completing the infection process. The internal environment after fruit bagging is an important condition for the occurrence of black spot disease.
For bagged apples in northern China, the initial onset period of black spot disease is early July, and the peak onset period is August, when rainfall is greatest. In some years, due to heavy rainfall in September, the peak onset period is postponed. After harvest, during storage and transport, the rate of diseased fruit no longer increases.
Factors affecting the occurrence of black spot disease
1. Rainwater. Because the apple's fruit stalk is relatively short, the bag opening cannot be gathered around the fruit stalk. Therefore, the bagging method used in production is the fold-and-press method. This method cannot prevent rainwater from running down the fruit stalk onto the fruit inside the bag. When there is very little rainwater in the bag, black spot disease is more severe at the stem cavity. When there is a lot of rainwater in the bag, disease on the fruit body is more severe.
2. Bagging method. When bagging, if the paper bag is not puffed out, or if the ventilation holes at the lower corners of the paper bag are not opened, the disease is more severe; if the bag opening faces upward, the disease is severe, while if the bag opening faces downward, the disease is mild.
3. Fruit bag quality. Fruit bags of different qualities differ greatly in air permeability. Using paper bags with good air permeability results in a lower disease rate.
4. Insect damage. Insect wounds on fruit after damage by Siteroptes, mealybugs (Pseudococcus comstocki), and green plant bugs (Lygus lucorum) can induce the occurrence of black spot disease.
Prevention and control methods:
1. Spraying for prevention. From after apple petal fall to before bagging, spray 3 times with fungicides, such as 800-1000 times dilution of Luo'an No. 3, 8000-10000 times dilution of Xingbiao, and 3000 times dilution of Wanxiu. Since the period after petal fall is also a critical period for controlling various pests, the above fungicides can be mixed with Hailiang, imidacloprid, and acetamiprid.
2. Choose high-quality fruit bags. The outer paper bag must be made of wood pulp paper made from coniferous tree raw materials, with moderate paper thickness, soft and fine toughness, good air permeability, strong light blocking, no water seepage, resistance to wind, sun, and rain, and tightly glued edges; the inner bag must not fade, have good wax quality with uniform wax coating, be water-resistant, and not melt under high temperature and sunlight. Film bags should be pressed from virgin polyethylene plastic film (do not use recycled film),
In areas with poor light, use red film. In plateau fruit areas with strong ultraviolet rays, use translucent milky white film bags that are not prone to sunburn.
3. Bag earlier. Bagging earlier allows young fruit to adapt to the environment inside the bag sooner, making the fruit surface more delicate. For film bags, 15-20 days after petal fall is suitable. For paper bags, 25-35 days after petal fall is suitable. For film bags plus paper, put on the paper bag 15-25 days after putting on the film bag. When bagging, the fruit bag should be puffed up, sealed tightly at the top, ventilated at the bottom, not wrinkled, not clinging to the fruit, and the fruit should hang in the center of the bag.
4. Manually remove floral organ residues. Experiments show that manually removing filaments and styles after apple petal fall can effectively prevent the occurrence of black spot disease in bagged apples, because it removes the material basis on which the pathogen depends for survival. This method can be combined with fruit thinning, moving the timing of fruit thinning earlier to the petal fall stage. This measure is highly time-sensitive and must be completed before the styles completely wither. Manually removing floral organ residues also has a clear effect on controlling apple moldy core disease.