Walnut canker
Distribution and harm of walnut canker occurred 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 of 20% ~ 40%, resulting in weak plant growth and even death.
Symptoms: Brown to black ulcer spots appear at the base of trunk and main branches, and then expand into spindle-shaped or strip-shaped lesions. For varieties with smooth bark, the lesions are soaked in water or form obvious blisters, which are filled with light brown liquid. After the bubble burst, the effluent turned dark brown when exposed to air, and remained around the lesion. Finally, the lesion shrank and sank, and the middle part cracked, with many small black spots scattered on it, namely, the daughter seat, conidia and ascomycetes of the pathogen. When wet, the small black spots overflow with white to milky conidia horns.
The pathogen belongs to the fungus Ascomycetes grape. The metastage is a group of Ascomycetes in the subfamily Hemiptera. The daughter seat is black and nearly round, in which one or several sac cavities are buried. Dark brown, oblate or pear-shaped, with papillary pores, with a diameter of120 ~ 289 microns. The ascus fasciculus is colorless, rod-shaped, with short handle and double wall, and the top wall thickness is easy to digest, 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. The conidia are solitary or clustered in the stroma, dark, spherical or oblate, with a diameter of 90 ~ 237 microns. Conidiophore is colorless and short. Conidia are colorless, long spindle-shaped to hammer-shaped,16 ~ 25 μ m× 4 ~ 6 μ m.
The pathogen of walnut ulcer is the same as that of poplar ulcer. Cross inoculation can infect each other. It is easier to get sick on poplars by planting seeds with walnut canker.
Disease cycle and epidemic bacteria overwinter in the disease group with conidia and ascospores. In the following spring, when the temperature rose and the rainfall was suitable, two kinds of spores spread by rain and invaded from lenticels or injured tissues of branches, resulting in disease spots and then forming conidia, which were reinfected by rain for many times. The pathogen of ulcer had latent infection characteristics, that is, the pathogen had invaded the body during the normal long March of the walnut branch revolution that year, but it showed no symptoms, and only when the plants encountered adverse environmental conditions and physiological disorders that year did they show obvious ulcer spots. Generally, low temperature in early spring, drought, strong wind and many branch wounds are easy to get sick.
Prevention and cure method
First, removing diseased dead branches and burning them centrally can reduce the source of infection.
Second, strengthen the management of the forest garden, dig deep and fertilize, strengthen the tree vigor and improve the disease resistance.
Third, the trunk is painted with white agent. The formula of the 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 solution of 50% etobuzin wettable powder or 200 times solution of 80% antibiotic "402" EC in April-May and August respectively has good control effect.
Fifth, curettage treatment. Scrape the bark of the diseased spot to xylem, or cut several cuts in the diseased spot vertically and horizontally, and then brush with 3-wave stone sulfur mixture, or disinfect the liquid medicine such as 1% copper sulfate solution or 40% thiram wettable powder 50-00 times.