How to prevent and treat bacterial crown gall disease in cherry blossoms

Bacterial crown gall disease is one of the most common root diseases on ornamental flowers and nursery stock in northern China, occurring mostly in areas with alkaline soil. Besides harming cherry blossoms, this disease can also harm Rosaceae plants such as elm and rose, as well as indoor and outdoor flowers and trees such as ginkgo and Dianthus, with its hosts covering more than 300 species in 60 families.

Symptoms

This disease often occurs at the root crown, especially at the graft union of nursery stock, and sometimes also occurs on lateral roots, branch roots or branches (canes).

The gall is spherical when it first forms, can merge with one another, and is milky white or slightly red; as the tumor grows, the interior becomes lignified and hard, the surface cracks and becomes rough, and it gradually turns brown to dark brown. The gall can be as small as a bean or as large as a fist. Diseased seedlings have fewer fibrous roots, grow slowly or have yellowing leaves that drop early, increased dead branches, a shortened flowering period, and may even die. The disease is very stubborn; even if the gall is removed, it often grows back.

Pathogen and infection cycle

The disease is caused by the Gram-negative bacterium Agrobacterium tumefaciens. The pathogen overwinters in the cortex of gall tissue or in the soil, and spreads through rainwater, irrigation water, long-distance transport of contaminated nursery stock, human factors, insects or root-knot nematodes causing wounds; it survives in the range of 10°C to 34°C, with an optimum humidity of 22°C, and is not prone to forming galls below 18°C or above 30°C; its acid-base tolerance range is pH 5.7 to 9.2, and it can cause disease within pH 6.2 to 8; in slightly alkaline, sticky continuous-cropping land, the higher the humidity, the more severe the disease; there is less disease in loose sandy loam soil.

Control measures

1. Strengthen quarantine for nursery stock leaving the nursery or coming from outside, discard diseased plants, and for suspicious nursery stock, soak the roots in 1% copper sulfate solution for 5 minutes, then place them in 2% lime water for 1 minute, or directly soak them in streptomycin solution for 30 minutes before planting and observing. 2. Apply 3% carbofuran granules at 30 g to 50 g per sq m, then plow the soil 15 cm to 20 cm deep and water thoroughly to kill root-knot nematodes and pests such as cutworms; grafting should avoid wounds contacting soil, and grafting tools can be disinfected with 75% alcohol or 1% formaldehyde solution. 3. When diseased plants are found, the tumor should be cut out together with its surrounding tissue; the wound can be disinfected with medical high-strength iodine tincture or streptomycin 400 international units, then coated with petroleum jelly to seal it; around the diseased plant, sulfur can be applied once at 50 g to 100 g per sq m, and a 500-fold dilution of 20% Tubaw wettable powder or a 150-fold dilution of 14% Duoxiaoling aqueous solution can be poured on for disinfection, after which the disinfectant solution should be poured once every half month, three or four times in total; 20 days after the gall is cut out, pour a 100 to 150 ppm solution of 50% indole powder to promote root growth and revitalize the diseased plant. Other treatments are the same as above; treatment is more effective when carried out in early spring or before the root system enters vigorous growth in summer.