Control Methods for White Root Rot in Hawthorn Cultivation

Hawthorn white root rot is an important root disease of hawthorn trees in old hawthorn-producing areas and is the main cause of death of old and weak trees.

I. Symptoms After infection, the roots are entangled with white to grayish-white silk-like nets, which are the pathogen's rhizomorphs, and a grayish-white thin downy substance is produced at the root crown area on the ground. Leaves become smaller and leaf margins scorch, and some or all of the small branches and large branches die back.

II. Transmission routes and disease conditions The pathogen mainly overwinters in the soil as mycelium, rhizomorphs, or sclerotia remaining on diseased roots. When conditions are suitable, sclerotia or rhizomorphs produce vegetative mycelium, which invades through lenticels in the root epidermis. The pathogen first infects new roots and then gradually spreads, and the damaged fine roots rot and become moldy. The pathogen spreads through contact between diseased and healthy parts or over long distances through infected nursery stock. The disease mostly breaks out from July to September. Its occurrence is related to soil moisture and pH, with humidity having the greatest effect. The disease is severe in low-lying, damp orchards or nurseries with poor drainage; overly dense planting, too-deep planting, excessive hilling, root injury during cultivation, and poor management easily lead to weakened tree vigor, and lack of soil organic matter and strong acidity can lead to the occurrence of the disease.

III. Control methods (1) Select and plant disease-free nursery stock. When establishing an orchard, select and plant disease-free nursery stock. If the nursery stock is confirmed to be diseased, it can be soaked for 1 hour in a 10% copper sulfate solution or 20% limewater or a 500-fold dilution of 70% thiophanate-methyl wettable powder before planting. It can also be soaked in constant-temperature water at 47°C for 40 minutes or at 45°C for 1 hour to kill the pathogen on the roots of the nursery stock. (2) Dig isolation trenches. Dig 1-meter-deep trenches outside diseased plants or diseased areas to create a blockade and prevent the disease from spreading in all directions. (3) Strengthen cultivation management, enhance tree vigor, and improve the tree's disease resistance. Use formula fertilization technology, do not apply excessive nitrogen fertilizer, appropriately increase potassium fertilizer, and keep the ratio of nitrogen, phosphorus, and potassium appropriate. During the full fruiting period, low-lying and damp orchards or plots should be drained. Prune rationally to prevent alternate bearing. Strengthen the control of other pests and diseases. (4) Treatment of diseased trees. When diseased trees are found, first dig down to the main root base, uncover the soil around the roots, look for lesions on the root crown, and then trace downward from the lesions to find the diseased points on the main root, lateral roots, and branch roots. For rotted roots, saw or cut them off from the root base, and at the same time carefully scrape off the diseased bark on the lesions of the root crown. If most of the root system is diseased, thoroughly remove all diseased roots, and during the process of removing diseased roots, carefully protect the healthy roots. The wounds must be disinfected by smearing or spraying with a high-concentration fungicide, then coated with Bordeaux mixture or other agents for protection. In addition, 1 part of 40% quintozene powder can be thoroughly mixed with 40-50 parts of new soil and then applied to the roots; for large trees 8-10 years old, apply 0.25 kg of medicated soil per tree. (5) Rotate the nursery. Severely diseased nurseries should be rotated with gramineous crops for 5-6 years before continuing to grow nursery stock.