How to prevent and control silver leaf disease in pear trees? Growers need to master these methods

In recent years, silver leaf disease has commonly occurred in pear trees in some areas of our city. This disease is a devastating fungal disease, and when it occurs severely, it can cause pear orchards to decline within a few years. After becoming diseased, pear trees weaken in vigor. Yield decreases, and severely diseased trees die 2-3 years later, seriously affecting pear production.

I. Damage symptoms

Silver leaf disease not only damages pear trees, but also damages many other fruit trees such as peach, apple, and jujube. The symptoms on affected fruit trees are mainly manifested on leaves and branches. Under the action of the pathogen, the leaf epidermis and mesophyll tissues separate, and the gaps become filled with air. Due to the reflection of light, the leaves appear pale gray with a slight silvery white luster, hence the name silver leaf disease; symptoms on branches are mainly manifested in the xylem. The pathogen in the xylem of diseased trees can spread upward to 1-2-year-old branches, turning the xylem of the diseased part brown, relatively dry, with a fishy odor, but the tissue does not rot. It can spread downward to the roots, and diseased roots are mostly decayed.

Affected fruit trees often first show symptoms on one branch, then gradually increase until the whole plant is diseased. Diseased trees sprout slowly, and leaves and fruits become smaller. On dead trees, imbricate purplish-gray fruiting bodies can be produced, but fruiting bodies are not produced on diseased trees that have not died.

II. Occurrence pattern

The pathogen of silver leaf disease is Chondrostereum purpureum, a fungus in the Basidiomycota, Agaricomycetes, Polyporales. Its optimum temperature range is 26°C. In winter, it overwinters in the xylem of diseased branches and trunks or on the branches and trunks of dead trees. Basidiospores spread with airflow and rainwater, and when conditions are suitable, they invade and infect plants through wounds. Generally, in May-June and September-October, when the tree body is rich in nutrients, this is the optimum period for pathogen infection and also a key period for prevention and control. It takes 1-2 years for affected fruit trees to develop symptoms after infection, which brings certain difficulty to prevention and control work. Therefore, fruit trees in diseased areas should take preventive measures.

III. Integrated control

1. Agricultural ecological control, strengthening orchard management

① Apply more fully decomposed organic fertilizer, improve the soil, strengthen tree vigor, and improve tree disease resistance.

② For orchards on flat, low-lying terrain, strengthen drainage facilities to prevent water accumulation in the orchard and poor growth of fruit trees.

③ Protect the tree body; prevent and control other branch and trunk pests and diseases, reduce wounds, and prune lightly. In diseased areas, top grafting for variety replacement is not advocated.

④ For relatively dense orchards, carry out appropriate transplanting to achieve a reasonable density and avoid wounds caused by mutual friction.

2. Manual control

① For severely diseased trees and dead trees, dig them out including the roots, dig out all root fibers, take them out of the orchard and burn them centrally, and disinfect the diseased holes with quicklime.

② Clean up the orchard, remove residual branches, diseased leaves, and diseased roots, and eliminate the source of disease.

③ After the soil where diseased plants were dug out is disinfected, replant other non-Rosaceae fruit trees to implement orchard renovation.

3. Chemical control

① For diseased plants with few diseased branches, adopt the branch-cutting therapy, that is, saw off the diseased branches and trunks. Note that all browned parts of the xylem must be sawed off cleanly. Apply Bordeaux mixture or 10 Baume degree lime sulfur mixture or 20% Shibaoling 1000-fold solution to the wounds to inhibit the spread of the pathogen.

② For lightly diseased plants, air-dry the roots, then spray leaves and irrigate roots simultaneously with 20% Shibaoling 3000-fold solution, or use copper 8-hydroxyquinoline sulfate (this pesticide needs to be imported and is expensive) by drilling holes in the trunk and burying it.

③ Before fruit trees sprout, apply 50 grams per mu of Baitan or Subaoli fungicide to the soil for obvious control and preventive effects.