How to prevent and control peach bacterial shot hole? A detailed guide to peach tree disease prevention and control methods
Peach bacterial shot hole is a widely distributed disease with a high incidence rate. Bacterial shot hole occurs in all peach-producing areas nationwide, especially in coastal and lakeside areas, in orchards with poor drainage, and in rainy years, where it often breaks out severely. If not controlled in time, it easily causes massive leaf drop, reduces nutrient accumulation, and affects flower bud formation. It not only weakens tree vigor and reduces the current year's yield, but also affects the following year's fruiting, resulting in poor harvests. Besides damaging peach trees, this disease can also infect various stone fruit trees such as plum, apricot, and cherry.
I. Symptoms of damage
It mainly damages leaves and can also infect branches. Leaf disease begins as water-soaked green small spots, which after expanding become round or irregular lesions, purple-brown to dark brown, varying in size, generally about 2 to 3 mm, with water-soaked margins and a yellow-green halo around the lesions. After the lesions dry up, a ring of cracks forms at the boundary between diseased and healthy tissue, and after falling off, a shot hole forms, or the lesion remains partially connected to the leaf.
After branches are infected, there are two different types of lesions: one called spring canker, and the other summer canker. Spring canker occurs on branches that grew in the previous summer (the pathogen invaded the previous year). In spring, when the first batch of new leaves appears, dark brown small blisters form on the branches, about 2 mm in diameter, later expanding to 1 to 10 cm in length, with width mostly not exceeding half the branch diameter, and sometimes causing branch dieback. In late spring (before and after flowering), the lesion epidermis ruptures, the pathogen exudes, and spread begins. Summer canker mostly occurs in late summer, on current-year young twigs, centered on lenticels, forming water-soaked dark purple spots. Later the lesions turn brown to dark brown, round or oval, slightly sunken, with water-soaked margins. Summer canker lesions do not easily expand and quickly dry up, so their role in spread is not significant.
II. Infection cycle and disease conditions
The pathogen of this disease overwinters in diseased branch tissue, mainly in spring canker lesions. In the second spring, as temperatures rise, the bacteria latent in the tissue begin to activate. Before and after peach flowering, the pathogen exudes from the diseased tissue, spreads via wind, rain, or insects, and invades through leaf stomata and branch lenticels. In northern regions, disease occurs in May, is more severe in early June, progresses slowly during summer drought, and becomes severe in the rainy season. The incubation period of the pathogen varies with temperature and tree vigor. When the temperature is 25°C to 26°C, the incubation period is four to five days; at 20°C it is 9 days; at 19°C it is 16 days; when tree vigor is strong, the incubation period can be as long as 40 days. Warm, frequent rain, or foggy seasons are suitable for disease development. Orchards with weak tree vigor, poor drainage and ventilation, or excessive nitrogen fertilizer application have more severe disease. Different varieties also have different degrees of susceptibility.
III. Prevention and control methods
Advocate the policy of "prevention first, integrated control," and follow the principle of "treat early, treat small, treat thoroughly." The following points must be achieved:
1. Strengthen orchard management: In winter, combined with pruning, remove diseased branches, thoroughly clean up dead branches, fallen leaves, fallen fruit, and dry grass, and burn them in a centralized manner to eliminate overwintering sources of the disease. Pay attention to orchard drainage, prune reasonably, make the orchard well-ventilated and well-lit, and reduce orchard humidity. Apply more organic fertilizer, avoid excessive nitrogen fertilizer, so that fruit trees grow vigorously and resistance to disease is improved.
2. Chemical control: Before peach trees sprout, spray 3 to 5 degrees Baumé lime sulfur mixture. From late May to late June, spray 65% wettable zineb 300 to 500 times solution once or twice. Spraying zinc sulfate lime solution also has good control effects; the formula is zinc sulfate 1 kg, lime 3 to 4 kg, water 150 to 200 kg.
3. Avoid mixed planting with stone fruit trees: When establishing a peach orchard, not only should the tree species be pure and disease-resistant varieties selected, but plum, apricot, cherry, and other stone fruit trees should not be planted nearby.