Symptoms and rules of pear brown spot disease, causes and control measures

Symptoms and rules of pear brown spot disease, causes and control measures

1 Symptoms and patterns

1.1 symptoms

At the beginning of the damaged pear leaves, gray spots with the size of 1~2mm appeared, with clear edges, and then gradually expanded and developed into oval or irregular large spots with gray center, brown periphery and black outer layer (Figure 1). When the disease is serious, the disease spots on the leaves can reach dozens, and the black spots are densely distributed, and the middle part of the late stage is gray. The periphery is brown, the outer layer is black, and the diseased leaves are easy to fall off.

1.2 occurrence regularity

Brown spot is a fungal disease overwintering on diseased leaves as ascocarp or conidia. After rain in the spring of the following year, spores are produced, spread by wind and rain and adhere to leaves after maturity. The incubation period of infected leaves is generally 5~12 days, and the longest is 45 days. Under suitable conditions, spores germinate and invade leaves, causing primary infection, and conidia are produced on leaves for secondary infection. Moisture is a necessary condition for the spore production and diffusion of overwintering pathogens. Dry and rotted diseased leaves could not produce conidia [1].

Brown spot disease can be seen in the whole growing season from the onset of pear leaves to defoliation. Generally, the disease is more serious from May to June in the local area. In terms of varieties, the snowflake pear of white pear line is the most serious.

Fig. 1 Pathogenesis of brown spot disease

2 Causes of disease

2.1 rainy

Much rain is the main condition of pear brown spot epidemic. High humidity and high temperature in rainy season easily induce pear brown spot. Rain also affects the sun in ultraviolet sterilization bacteriostatic effect play. For example, from July to September 2015, the rainy days in Liaocheng City reached 13,14 and 7 days respectively, especially from July 14 to 18, with rainy days for 5 consecutive days. The orchard was in high humidity environment for a long time, and the spread and infection of brown spot disease were serious.

2.2 orchard closure

Pear orchards in Liaocheng City basically adopt dense planting cultivation. In addition, fruit growers keep too many branches in shaping and pruning, and do not pay attention to summer pruning. The orchards are closed and the ventilation and light transmission conditions are poor, which leads to the moisture in the orchards not being effectively discharged. The orchards are in high humidity environment for a long time, resulting in serious brown spot disease.

2.3 irrational fertilization

In order to maximize the yield of pear orchard in short term, many fruit growers often apply nitrogen fertilizer and neglect the application of phosphorus, potassium and organic fertilizer, resulting in unbalanced fertilization, which not only causes the taste of pear fruit to decline, but also seriously affects the normal growth of pear trees, reduces the disease resistance of trees, and leads to the occurrence of brown spot disease.

3 Methods of Prevention

3.1 artificial control

Qingyuan. The garden after autumn. The pathogen of brown spot mainly overwinters on fallen leaves. After falling leaves, the leaves in the garden should be removed in time and buried deeply or burned. This is a simple and effective method to eliminate the pathogen and control the disease. 2. Clear gardens in growing season. Remove weeds in pear garden in time to ensure ventilation and light transmission in pear garden. In the growing season, the diseased leaves, diseased fruits and diseased shoots of pear orchards shall be removed in time and burned down in a centralized manner.

Scientific fertilization. Increase organic fertilizer and phosphorus and potassium fertilizer to maintain healthy growth of trees and improve disease resistance of trees. Base fertilizer is applied after harvest to before defoliation, mainly composed of completely decomposed organic fertilizer, combined with appropriate amount of chemical fertilizer and trace element fertilizer, balanced fertilization, and the amount of base fertilizer should reach 70%~80% of the total amount of fertilizer applied throughout the year. The fertilizer application amount in flower bud stage accounts for 20%~30% of the fertilizer application amount in the whole year. The ratio of N, P and K is 1∶0.5∶1. The yield of 50kg pear requires 0.20~0.25 kg pure N.

Drainage. Pay attention to pear garden drainage after rain to reduce humidity in the garden and reduce the occurrence and spread of diseases.

Reasonable pruning. Strengthen the management of pear orchards, timely thinning flowers and fruits for trees with heavy load; thinning orchards with excessive planting density; pruning trees with excessive branches and leaves in time, thinning out over-vigorous, over-dense and inner bore branches, improving ventilation and light transmission conditions of trees, and avoiding branches and leaves.

3.2 chemical control

During early spring pear leaf development period, Bordeaux mixture was sprayed in early and middle April to control pear rust, once every 10 days or so, 3 times continuously, and the ratio was 1∶2∶200. In rainy season, spray Bordeaux mixture once again, the ratio is 1∶2∶240. After pear blossoms, spraying 800 times solution of 70% thiophanate-methyl suspension or 1500 times solution of 50% benomyl wettable powder once every 15~20 days, generally spraying 2~3 times, can achieve good control effect. In addition, 800 times solution of 50% carbendazim WP and 2500 times solution of 12.5% terbuzole have good effect on controlling brown spot, and have no phytotoxicity, which are ideal medicaments for controlling pear brown spot at present [3].