Powdery mildew of Schisandra chinensis

1. Disease symptoms: Powdery mildew damages the leaves, fruits and new shoots of Schizandra chinensis, among which the young leaves and young fruits are most seriously damaged. Often caused by dry leaves, shoot death, fruit shedding. At the early stage of leaf damage, needle-like spots appeared on the back of leaves, gradually covered with a layer of white powder, and extended to the whole leaf when it was serious. The diseased leaves change from green to yellow, curl upward, wither and fall off. The disease began near the ear axis, and gradually expanded to the whole ear when it was serious. The diseased fruit wilted and dropped, and black and brown spots appeared on the fruit stalk and new shoots. At the late stage of disease, a large number of small black spots appeared on the main veins, branch veins, petioles and new shoots of the leaf back, which were cleistocapsid of the pathogen.

2. Pathogenesis rule: After identification, the disease is caused by Ascomycetes subphylum Cladosporium fungi. The sexual state of the pathogen is Cladosporium schisandra, which is an ectoparasite. The white powder of the diseased part is the mycelium, conidia and conidia of the pathogen. Mycelium leaves are bifacial, also borne on petioles; conidia are solitary, colorless, elliptic, ovate or subcylindrical; cleistocysts are scattered to aggregated, oblate, dark brown, accessory filaments are mostly 10-14, 0.8-1.5 times the diameter of cleistocyst, base is 8.0-14.4μm thick, straight or slightly curved, individual geniculate. The outer wall is rough at the base, smooth upward, septate or a few septate below the middle, colorless or light brown at the base and septate, and the tip is mostly 5-6 times bifurcated; 4-8 asci, elliptic, ovate, broadly ovate, 5-7 ascospores, colorless, elliptic, ovate.

High temperature and drought conditions are conducive to the incidence of disease. In Northeast China, the onset period is from late May to early June, and the peak period is reached in late June (if there is no drought and high temperature weather, the incidence is mostly in the first and middle of July). The environmental conditions such as over-dense branches, excessive growth, over-application of nitrogen fertilizer and poor ventilation were favorable to the occurrence of disease. The fungus overwinters in the form of mycelium, ascospores and conidia in the field. From the middle of May to the first ten days of June of the next year, the average temperature rose to 15-20℃, and the overwintering conidia on the diseased plants in the field began to germinate. With the help of rainfall and dew, they began to germinate and infect the plants, and the disease in the field originated. The middle of July was the peak period of conidia diffusion, the rate of diseased leaves and stems rose sharply, and a large number of fruits were infected. In the middle of October, the temperature dropped obviously, the leaves of Schizandra chinensis were senescent and fallen off, the diseased bodies scattered in the field, and the pathogens carried on the diseased bodies entered the winter dormancy period. Under natural conditions, the conidia produced by overwintering pathogen continuously cause reinfection by air flow transmission, and the disease can develop; the seedlings and fruits infected with powdery mildew spread far away by vehicles and ships, which is the most important transmission route of powdery mildew.

3. Prevention and control technology. Strengthen cultivation management, pay attention to the rational distribution of branches, improve the ventilation and light transmission conditions of the frame surface by pruning; appropriately increase the proportion of phosphorus and potassium fertilizer to improve the disease resistance of the plant and enhance the tree vigor. (2) Remove the source of bacteria, clean up the diseased branches and leaves before germination, cut off the diseased ears in time at the early stage of disease, pick up the diseased fruits, burn them or bury them deeply, and reduce the infection source of bacteria. (3) Chemical control: spray 1:1:100 times of Bordeaux mixture in late May for prevention. If there is no disease, spray once every 7-10 days; choose 0.3-0.5 Baumede-sulfur mixture, or 800 - 1000 times of 25% triadimefon wettable powder, or 800 - 1000 times of thiophanate-methyl wettable powder, spray once every 7-10 days, spray continuously for 2-3 times, and the control effect is very good; spray 400-500 times solution of 40% sulfur colloidal suspension, or 15% triadimefon emulsifiable concentrate 1500-2000 time solution, or 25% azoxystrobin aqueous suspension 1500 times solution, or 50% kresoxim-methyl dry suspension 3000-4000 times solution, spraying once every 7-10 days, spraying twice continuously; or selecting fungicides such as Xiansheng, Nitrile, shellfish extraction, etc. for prevention and control.