Control of frost blight of growing litchi

Litchi from young fruit to ripe fruit, fruit stalk and fruiting branchlets can be damaged by litchi downy blight, and the leaves can also occur at high humidity.

Local chlorosis on the symptomatic leaves, white mold layer on the back, the fruiting body of the pathogen, but usually in the peak period of the disease, the leaves have been aging, so the damage of leaves in the field is very rare. When the fruit is injured, the disease spot is irregular, there is no obvious edge, the disease spot grows white mildew layer when wet, the disease spot expands rapidly, the whole fruit often turns brown, the flesh turns sour, decays into pulp in the later stage, and flows out brown water. The young fruit falls off soon after it is damaged, and the disease grows white mildew. Etiological principle Peronophythora litchii Chen ex Ko et al. It is called litchi downy Phytophthora, which belongs to flagellum subphylum fungi. The sporangium pedicel was 5-7PyA wide and 92-1332 μ m long, but on cornmeal medium, the sporangium was extremely long, even more than 1000 μ m long, colorless and diaphragmatic. After 3 times of single branch 2Mel, the apex of the branch was doubly bifurcated, the tip of the terminal peduncle was slightly pointed, and a sporangium was formed at the same time. On cornmeal medium, most of the new sporangium peduncles are produced at a distance from the top of the previous sporangium, or continue to form in the axils of the branches, and sometimes form new sporangium without sporangium on one terminal peduncle, or push the sporangium to one side and extend the sporangium, and its top branch forms sporangia at the same time, each sporangium pedunculates more than ten sporangia. The sporangia are lemon-shaped, colorless or slightly yellowish, with papillae at the top, with a small handle at the base of the sporangium, and usually form zoospores that escape from the apical nipple. On the cornmeal cabbage medium, the oospore is spherical, colorless, thin and smooth, 23mur33 × 17mur27 (μ m); the male organ is mostly perinatal, a few lateral, colorless; the oospore is spherical, colorless to yellowish, and the wall is smooth. Oospores can also form oospores on the host branchlets in the later stage, but they are rare. The pathogen may overwintering on diseased fruits and leaves by mycelium. In the late spring and early summer of the following year, sporangia spread with wind and rain, and sporangia produced zoospores to invade host leaves or fruits. Humidity is the key factor for the prevalence of the disease. During the rainy season, litchi orchard has low-lying terrain, poor drainage, luxuriant branches and leaves, and poor ventilation, which can aggravate the occurrence of the disease. In addition, near-mature fruits are susceptible to disease, while early and middle ripening varieties (such as "Dingfeng", "black leaf", etc.) are susceptible to disease. From the end of April to the first ten days of June in Guangzhou, the average temperature is 21 ℃ in April and May, 25 ℃ in the first ten days of June, and the lowest temperature is 11 ℃. The pathogen harms litchi by zoospores, the infection process is short and the re-infection is frequent, so it is often popular in production. The control method (1) eliminate the primary infection source. Late autumn and early winter, combined with Qingyuan thoroughly remove the residual leaves, residual fruit and fallen leaves, fallen fruit, concentrated burning. (2) strengthen the management of orchard. Pay attention to drainage in low-lying waterlogged land and properly cut off overgrown branches to enhance permeability. (3) Pesticide control Spray 72% Kangling wettable powder 800 times, 70% ethyl phosphine manganese zinc wettable powder 500 times, or 58% metachlorothalonil manganese zinc wettable powder 800 times, 75% chlorothalonil 600 times, 90% aluminum triethyl phosphate 500 times, 64% alum 400 times, 60% chlorothalonil 500 times before fruit ripening. Once every 10 days or so, prevention and treatment for 4 times.