How to control crown gall disease of jujube trees with good results
This disease is a bacterial disease and occurs in jujube-growing areas in the north. After the roots are damaged, the aboveground growth is slow and the plants are stunted; in severe cases the leaves turn yellow and fall early, and the branches weaken or even die, but it rarely causes the whole plant to die. Besides harming jujube trees, the pathogen also attacks apple, pear, peach, Chinese chestnut, persimmon, plum, walnut, poplar, willow, and so on.
(1) Symptoms
It mainly occurs at the root crown of jujube trees, and also occurs on the main roots and lateral roots; in a few cases it can occur above the ground. A gall forms on the damaged part, initially blue-gray or flesh-red, smooth and soft; later, as the gall enlarges, it turns brown or dark brown, becomes hard in texture, and its surface becomes rough, cracked, or uneven. Some galls later become decayed.
(2) Pathogen
It belongs to the crown gall bacterium of the genus Agrobacterium among bacteria. The bacterial cells are short rod-shaped, single or in chains, 1.2-5 micrometers long and 0.6-1 micrometer wide, with 1-4 peritrichous flagella. It has a capsule and no spores. Gram stain reaction is negative.
(3) Occurrence pattern
The crown gall bacterium overwinters in the cortex of the gall and on the remains of diseased galls in the soil. It spreads through rain and irrigation water, and the activity of underground pests also plays a certain role in spread. Infected nursery stock is an important route of long-distance spread. The bacterium invades through wounds, stimulates plant cells to divide rapidly, produces a large amount of meristematic tissue, and forms gall symptoms. Under moist and warm soil conditions, or in alkaline soil with many wounds caused by underground pests, the disease is favored. Grafting can also transmit the disease.
(4) Control methods
1. When grafting, do not take scions from diseased trees;
2. When raising seedlings, do not raise them in diseased land;
3. When transporting nursery stock, strictly carry out plant quarantine, remove diseased seedlings and burn them, and disinfect healthy seedlings by soaking the roots for 10 minutes in 0.5% copper sulfate or 800 times thiophanate-methyl, carbendazim, etc.
4. For lightly diseased plants, dig away the soil around the roots, expose the roots to sunlight, cut out the galls, disinfect with 0.1% mercury water, and then apply Bordeaux mixture to protect the wounds.
5. Strengthen the control of underground pests.