How to prevent and control peach bacterial shot hole disease? Detailed methods

Peach bacterial shot hole disease is a widely distributed disease with a high incidence rate. Bacterial shot hole disease occurs in all peach-producing areas across the country, especially in coastal and lakeside areas, orchards with poor drainage, and in rainy years, where it often occurs 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, causing poor harvests. Besides harming peach trees, this disease can also infect various stone fruit trees such as plum, apricot and cherry.

I. Damage symptoms

It mainly harms leaves and can also infect branches. When leaves are affected, water-soaked green small spots appear initially, which after expanding become round or irregular lesions, purple-brown to dark brown in color, with lesion sizes varying, generally about 2 to 3 mm. Around the lesions there is a water-soaked appearance with a yellow-green halo. After the lesions dry up, a ring of cracks forms at the junction between the diseased and healthy tissue, and after falling off, a hole forms, or part remains connected to the leaf.

After branches are affected, there are two different types of lesions, one called spring canker, and the other summer canker. Spring canker occurs on branches grown in the previous summer (the pathogen had already 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 the width mostly not exceeding half the branch diameter, and sometimes causing branch dieback. In late spring (before and after flowering), the epidermis of the lesions 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 edges. Summer canker lesions do not easily expand and dry up quickly, so their role in spread is not significant.

II. Infection cycle and disease occurrence conditions

The pathogen of this disease overwinters in the diseased branch tissue, mainly overwintering in spring canker lesions. In the second spring, as temperatures rise, the bacteria lurking in the tissue begin to become active. Before and after peach flowering, the pathogen exudes from the diseased tissue, spreads by wind and rain or insects, and invades through leaf stomata and branch lenticels. In northern regions, the disease occurs in May, becomes 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 occurrence. Orchards with weak tree vigor, poor drainage and ventilation, and excessive nitrogen application all have more severe disease. Different varieties also differ in disease severity.

III. Control methods

Advocate the policy of "prevention first, integrated control," and according to 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, etc., and burn them in a centralized manner to eliminate overwintering sources of the disease. Pay attention to orchard drainage, carry out reasonable pruning, make the orchard well ventilated and well lit, and reduce orchard humidity. Increase the application of organic fertilizer, avoid excessive nitrogen fertilizer, so that fruit trees grow vigorously and their disease resistance is improved.

2. Chemical control: Before peach trees bud, 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 be selected, but plum, apricot, cherry and other stone fruit trees should not be planted nearby.