(Shao Liping)
Japanese, Korean and China. At the beginning of the disease, 2 ~ 3 yellow spots appeared from the tip or middle of the blade, and gradually expanded into reddish-brown spots. In severe cases, the whole leaf turns reddish brown, which looks like a fire from a distance and withers ahead of time. For example, when this disease occurs year after year, this tree tends to decline and its growth is frustrated. The pathogen is coccidia of Larix kaempferi. Ascomycetes and ascospores are produced in the cavity of fallen leaves in spring, and ascospores are released in June. From late June to early July, the concentrated release of ascospores accounted for about 50% of the total amount of the year. Ascomycetes spread with the wind, and the adhesive film on the surface of Lai spore adhered to larch leaves, and was invaded by stomata after germination. After 15 ~ 30 days, the leaves appeared diseased spots and gradually turned reddish brown. From the end of July to the end of August, tiny black spot spore apparatus appeared on the diseased spot, and defoliation began in the middle and late August (about 30 ~ 50 days earlier than the normal defoliation period). By the end of September, two more tender leaves had grown, freezing to death in winter. The leaves are yellow and twisted, and soon there will be a black-dot sac on the ground to winter. Sex spores are not contagious and occur once a year. When the temperature reaches 20℃ and the air humidity reaches above 75% after larch leaves fall, it is beneficial to the occurrence and epidemic of diseases. Diseases are serious in low temperature, high humidity and rainy years. Broken wood and forest path of Mu Yi's disease. When the forest age is more than 20 years, the disease is light or not. Mixed forests or forests with more undergrowth vegetation, as well as timely care, the diseases are relatively minor. 19 At the end of 1970s, China determined the disease classification standard and statistical method of disease index, found out that the economic allowable level of disease was that the disease index was less than 30, and stipulated that the disease management index was that the disease index was greater than 40. According to the relative humidity (x 1), precipitation (x2) and extreme high temperature (x3) in July, the prediction formula of multiple regression equation is put forward. The disease is divided into five grades, 1 no disease, the leaves of the second crown 1/4 turn yellow-green, the leaves of the third crown 1/2 turn yellow-green, the leaves of the fourth crown turn yellow-green, and all the leaves of the fifth crown turn brown. Every year, the disease index of that year can be predicted according to the local meteorological forecast data, and then the management level and measures can be determined.
Prevention and control methods: Unclosed nurseries and young forests should be sprayed with mancozeb and Dyson for prevention; If the predicted disease index of closing hillsides to facilitate afforestation is greater than 40, treat it with sodium pentachlorophenol smoke after the rain in late June and early July; To build an artificial forest, we should pay attention to breeding disease-resistant tree species, adhere to the principle of adapting trees to the right place, rationally mix them, strengthen tending, and prune and thinning them in time after forest formation.