Walnut saplings planted the year before last and the year before last did not know what disease they got last winter. Now it is about 1.5 meters high, but there are many black holes on the trunk.

Walnut canker

Walnut canker occurs in both northern and southern walnut producing areas in China. It mainly harms the trunk, shoots and fruits of young trees, with a general incidence rate of 20% ~ 40%, which leads to plant growth weakness and even death.

Symptoms: Brown to black ulcer spots appear at the base of trunk and main branches, and then expand into spindle or strip lesions. For varieties with smooth bark, the diseased spots are soaked in water or form obvious blisters, which are filled with light brown liquid. After the bubble bursts, the effluent turns dark brown when exposed to the air and stays around the lesion. Finally, the diseased spot shrinks and sinks, and the middle part is cracked, and there are many small black spots scattered on it, that is, the spores, conidia and ascomycetes of pathogenic bacteria. When wet, black spots overflow from white to milky conidia.

The pathogen belongs to grape ascomycetes. Yatai is a group of ascomycetes in Hemiptera. The submount is black, nearly round, and contains one or several sacs. Dark brown, oblate or pear-shaped, with papillary pores, with a diameter of 120 ~ 289 microns. The ascus bundle is colorless, rod-shaped, short-stalked, double-walled, and the thickness of the top wall is digestible, 50 ~ 72 μ m×16 ~ 20 μ m. Ascomycetes are colorless and oval, with one end slightly spindle-shaped, 20 ~ 23 microns × 5 ~ 7 microns. Conidia are solitary or clustered in the matrix, dark in color, spherical or oblate, with a diameter of 90 ~ 237 microns. Conidia are colorless and short. Conidia are colorless, spindle-shaped to hammer-shaped,16 ~ 25 μ m× 4 ~ 6 μ m.

The pathogen of walnut ulcer is the same as poplar ulcer. Cross inoculation can infect each other. Planting seeds of walnut canker on poplar is more likely to get sick.

Disease cycle and epidemic bacteria overwinter in the disease group with conidia and ascospores. In the following spring, when the temperature rises and the rainfall is suitable, the two kinds of spores spread by rain, invade from lenticels or branches, form conidia after producing lesions, and are reinfected by rain for many times. The pathogen of ulcer has the characteristics of latent infection, that is, the pathogen has invaded the body during the normal long March of walnut branch revolution, but it has not shown symptoms. Only when the plant encounters adverse environmental conditions and physiological obstacles in that year, it shows obvious ulcer spots. Generally, early spring is characterized by low temperature, drought, strong wind and many branch injuries, and it is easy to get sick.

Prevention and cure method

First, removing diseased dead branches and centralized incineration can reduce the source of infection.

The second is to strengthen the management of forest gardens, dig deep into fertilization, enhance tree vigor and improve disease resistance.

Third, the trunk is whitened. The formula of whitening agent is 5 kg of quicklime, 2 kg of salt, 0. 1 kg of oil, 0. 1 kg of bean flour and 20 liters of water.

Fourthly, spraying 200 times of 50% ethisulfuron wettable powder solution or 200 times of 80% antibiotic "402" EC solution in April-May and August respectively has good control effect.

Fifth, curettage treatment. Scrape the bark of the diseased spot to the xylem, or make several deep cuts in the diseased spot vertically and horizontally, and then brush with 3 waves of mixed solution of stone and sulfur, or disinfect with 50-00 times of 1% copper sulfate solution or 40% thiram wettable powder.