Symptoms and Control Methods of Crown Gall Disease in Fruit Trees

Crown gall disease in fruit trees is a very common disease. If it is not controlled in time, it may reduce yields and even cause the death of fruit trees. Therefore, fruit growers must do a good job of prevention and control. So what are the symptoms of crown gall disease in fruit trees? How should it be controlled?

I. Main symptoms of crown gall disease

Spherical or flattened spherical tumors form at the affected sites. The tumors vary in size, as small as a bean grain and as large as a fist, and many small tumors may also cluster together into a larger cancerous growth whose diameter can reach tens of cm. Newly formed tumors are milky yellow and gradually become light brown to dark brown. The internal tissue is grayish white, soft, or spongy. In the later stage, the internal tissue becomes lignified. The outer surface is rough and uneven. Some fine roots grow on its surface or around it. The surface tissue of mature diseased tumors ruptures, or rot spreads from the surface layer toward the center. Some tumors fall off from the base, and new diseased cancers may also grow again. After fruit trees develop crown gall disease, their growth and development are severely hindered, the tree vigor gradually weakens, fruiting is poor, and quality declines. Therefore, orchard cultivation managers must pay attention to the prevention and treatment of crown gall disease in fruit trees.

II. Characteristics of crown gall disease in fruit trees

Crown gall disease in fruit trees mainly invades host plants through wounds. After the pathogen invades the plant, it can continue to multiply in the intercellular spaces of the cortical parenchyma cells and secrete irritating substances, causing neighboring cells to divide and proliferate faster, forming cancerous tumors. The onset of crown gall disease in fruit trees has the following characteristics:

1. Damage can occur during every year's growing season, with the most occurring in August.

2. Slightly alkaline soil favors the disease, while acidic soil has less disease.

3. Sandy loam soil with high humidity favors the disease, while heavy clay soil has less disease.

4. Wounds caused by grafting seedlings, lifting seedlings, planting, mounding soil for cold protection, and intertillage easily lead to the disease.

5. The degree of disease varies among different species. Peach trees are affected more, while apricot trees are affected less.

6. The degree of disease varies among different rootstocks. Sweet cherry grafted on Prunus incisa is highly susceptible, while that grafted on Prunus sargentii is highly resistant.

7. Disastrous weather leads to worsened disease, such as freezing damage and hail damage.

8. Damage from other diseases and pests leads to an increase in cancerous tumors, such as soil insects and nematodes.

III. Control measures for crown gall disease in fruit trees

1. Self-propagate disease-free seedlings. Select rootstocks with relatively strong disease resistance and disease-free scions, and raise seedlings in fields with no disease history and no trees. Apply no chemical fertilizer or little chemical fertilizer, and cultivate strong seedlings.

2. When purchasing seedlings externally, inspect the disease situation and use the “five no-buy” principle to guide purchasing work, namely: do not buy seedlings raised the same year and released from the nursery the same year; do not buy seedlings forced with chemical fertilizer; do not buy seedlings with a disease history and galls; do not buy seedlings with susceptible rootstocks; and do not buy seedlings affected by hail damage, freezing damage, and with many soil insects.

3. Seedlings must be quarantined and protected against disease. Check seedlings one by one carefully. Those with disease should be burned in a centralized manner (do not leave future trouble). Soak the selected seedlings with the “K84” biocontrol agent or treat them with other agents.

4. Treat seedlings before planting. Before or at planting, dip the roots in a 100-fold copper sulfate solution for 10 minutes, wash them, and then dip them in Bordeaux mixture for protection. At the same time, use 50% phoxim poison bait to control soil insects.

5. Prevent seedling injury. In links such as lifting seedlings, transport, planting, and management, try every effort to prevent injury to seedlings.

6. Prevent freezing damage. Pay special attention to cold protection at the seedling stage. Management measures for mature trees should be appropriate to improve cold resistance.

7. Inspection after planting. After planting, once diseased plants are found, they must be immediately pulled out and burned. Replace the original tree pit with new soil, and it is best to replant after one year.