How to prevent and control larch shoot blight in North China larch?
Larch shoot blight is a serious disease in North China larch forests and one of China's forestry quarantine pests. So what are the prevention and control methods for larch shoot blight in North China larch?
1. Symptoms of larch shoot blight in North China larch
This disease occurs only on the new shoots of the current year. It generally starts from the terminal shoot first, then gradually spreads downward from the blighted shoots in the upper part of the crown. The stem or stem axis gradually loses its green color, changing from light brown to brown, wilting and becoming thinner. The tip of the shoot bends and droops in a hook shape, and leaves gradually fall from the bent part; in the later stage, only dead leaf clusters remain at the tip of the shoot, persisting for a long time without falling, and appearing purplish-gray.
New shoots that become diseased later have already become woody; the diseased branches do not bend and droop but instead form upright-type shoot blight, and all diseased leaves fall off. Therefore, the shoots above the diseased part die, turning the seedlings into topless seedlings. Resin masses that adhere and do not fall are often present on the diseased shoots.
On young trees, the new shoots of the following year also become diseased and die in the same way, and small branches growing from lateral buds replace the original terminal shoot. In this way, the disease occurs year after year, the blighted shoots form clusters, the crown becomes broom-like with clustered branches, height growth stops, stunted little old trees form, and even the whole plant may die.
2. Prevention and control methods for larch shoot blight in North China larch
1. Remove diseased and dead branches, burn them in a centralized manner; this can reduce sources of infection.
2. Strengthen forest and garden management, deep plow, and apply fertilizer to enhance tree vigor and improve disease resistance. In spring and autumn, open holes in the tree pits and apply fertilizer. The amount of fertilizer can be considered as appropriate according to the size of the tree. Generally, a 10-year-old tree can be given 300 grams of compound fertilizer per plant at a time, applied once in spring and once in autumn. When preventing and controlling the disease, fertilization must be coordinated; when fertilizing, note that in spring more fertilizer with a relatively high nitrogen content should be used, while in autumn more fertilizer containing relatively more phosphorus and potassium must be applied.
3. Brush the tree trunks with whitewash. The formula for the whitewash is 5 kg quicklime, 2 kg salt, 0.1 kg oil, 0.1 kg bean flour, and 20 L water.
4. In April to May and in August, spray 200-fold dilution of 50% thiophanate ethyl wettable powder, or 200-fold dilution of 80% antibiotic emulsifiable concentrate; both have relatively good control effects.
5. Scrape off diseased spots for treatment. Forcefully scrape away the bark of the diseased spots down to the xylem, or deeply cut crisscross slits into the diseased spots, then brush with 3-degree lime sulfur mixture, or disinfect with 1% copper sulfate solution, or 50-00-fold dilution of 40% asomate wettable powder and other medicinal liquids.
6. Rational irrigation. In dry seasons, open holes and water promptly, and be sure to water thoroughly; after it dries thoroughly, water a second time; drain promptly during the rainy season; before freezing, water thoroughly with winter water. The following spring, if the soil is relatively moist, control watering; otherwise, water thoroughly, to prevent excessive needle shedding caused by drought and weakened tree vigor. When watering, follow the principle of not watering if not dry, and watering thoroughly when watering.