Spruce snow mildew

[distribution and harm] the disease occurs in North America, Northern Europe, Japan and other countries, harming fir (Abies), spruce (Picea), willow (Cryptomeriafortunei) and other tree species. In China, it is distributed in forest areas such as western Tianshan, western Junggar and Altai Mountains. The main affected areas are Gongliu, Yining, Tacheng and other places. Seriously ill nursery, the annual loss rate is 330.62%. In the artificial regeneration of young forest, the disease is also very serious, especially when reforestation with small seedlings, weak seedlings and diseased seedlings. In recent years, due to the harm of snow mildew, resulting in shortage of seedlings, decline in quality, low survival rate and preservation rate, affecting the recovery and development of forest resources.

[symptoms] the needles and aboveground whole plants are infected under snow, covered with grayish brown to dark brown hyphae, or invade the interior, causing mildew and asphyxiation of seedlings. The texture and thickness of the mycelium vary according to the disease, flocculent when the disease is mild, and felt when it is severe. The color varies according to the length of time the victim is brown in the early stage and white or beige in the event of melting snow. When the damage is mild, it is a mass. After melting snow, the diseased leaves fall off, the cortex of the stem fester, and the aboveground parts gradually die.

The main pathogens are BotrytiscinereaPers., Sclerotiniasclerotiorum (Lib.) DeBary, Truncatella, Cladosporiumsp., Rhizopussp., Alternariasp., Epicoccumsp. And so on. The morphology of the main pathogens is described as follows:

1. The pseudosclerotia of Botrytis cinerea is nearly black, the surface is rough, nearly round to irregular, 0.1~1mm on the leaf, 2~3mm on the stem, semi-exposed at maturity, not easy to fall off. The vegetative hyphae are colorless and transparent and contain many granules, 4 ~ 11 μ m wide. Conidiophores are produced from sclerotia and hyphae. The base of conidiophores is light brown, tapering upward, nearly colorless, long 0.5~2mm, 8 ~ 16 μ m wide, branched many times at the tip, branchlets expand to form small peduncles, and budding conidia gather in clusters. Conidia colorless, unicellular, oval, ellipse to rectangular, 8 ~ 18 μ m × 7 ~ 12 μ m. Old conidiophores flattened and twisted, brown. In addition to the terminal conidia, the conidia are interspersed on the extended conidiophores, with an interval of 26 ~ 59 μ m. The attachment spores are dichotomous in the early stage and assemble in the later stage, dark green to black. Microspores colorless, suborbicular, about 3 μ m.

2. The sclerotia of Sclerotinia sclerotiorum is black, smooth, broad bean-shaped, sub-bell-shaped or nearly round, 4~8mm. Born on the young stems, branchlets, cotyledon nodes and new bud tips of spruce, occasionally on the leaves, easy to fall off. Generally, the hyphae are produced by sclerotia, the hyphae are colorless and transparent, and the attached spores are dark green to black. It can also produce 1-15 ascomycetes from one sclerotia, usually 4-6. The ascus disc is light to dark flesh color, cup-shaped at the initial stage, disk-shaped after expansion, 1~11mm in diameter and 1~2cm in length of the stalk, which often varies according to the environment and can be as long as more than 4cm. The solid layer is nearly colorless, the ascus is rod-shaped, 108 ~ 145 μ m × 6 ~ 8 μ m, and the apical ring is stained with iodine solution to turn blue. There are 8 ascospores, uniseriate, unicellular, mostly oval, 8 ~ 12 μ m × 5 ~ 8 μ m, containing 2 or 3 oil droplets. The lateral filament is slightly longer than the vesicle and the tip is slightly enlarged.

3. The conidium of Phaeosporium is cauline, flask-shaped to discoid, buried, dispersed or confluent, 250 ~ 1100 μ m × 100 ~ 450 μ m, with brown, polygonal cells and irregular dehiscence. The fruiting layer is peripheral, the conidium is colorless, linear, 25 ~ 46 μ m × 2 μ m, less septate, with 1 to 3 annuli. The conidia are spindle-shaped, 16 ~ 21 μ m × 6 ~ 9 μ m, 3 true septum, the middle two cells are brown, 11 ~ 14 μ m long, the basal cells are truncated, the apical cells are conical and colorless, and the apical cells have elongated accessory filaments, variable in shape, dichotomous or irregularly branched, sometimes simple.

Snow mildew is harmful not only to P.schrenkiana and P.obovata, but also to P.abies, P.glauca, P.crassifolia, P.balfouria7la and so on. Spruce snow mildew continued to develop and spread under the snow after it fell ill during the growing period. Early winter and early spring are the main occurrence periods, and spread rapidly in early spring. The common characteristics of the three pathogens such as Botrytis cinerea are: at 0: 22 ℃, the growth increases rapidly with the increase of temperature; above 28 ℃, the growth is extremely slow and gradually stagnant; below 22 ℃, the vegetative growth is exuberant. Mature sclerotia, generally without dormancy. It can germinate when the temperature and humidity are suitable. In the western Tianshan Mountains, the western Junggar Mountains and the Altai Mountains, the snow cover is deep (take Xinyuan Burjin as an example), and the average maximum snow depth over the years is 100.4cm. Under the snow cover, the soil does not freeze in winter, or only in a few years, the shallow soil layer freezes slightly for a short time. The seedling canopy and soil layer have been in a state of low temperature and high humidity of about 0 ℃ for a long time. As the surface temperature covered by snow is about 0 ℃ in recent 5-6 months, the temperature above 0 ℃ lasts for nearly 2 months from March to April. Such ecological conditions are suitable for the occurrence of snow mildew, especially the unstable temperature in early winter and early spring, the postponement of snow melting period, the frequent occurrence of freezing rain, sleet, the formation of ice cap under the snow layer, the seedling being pressed down and poor air permeability. it is more conducive to the development and spread of the disease. The pathogens are weak parasites, various natural and man-made injuries such as frostbite and burns of seedlings, as well as extensive management, continuous cropping for many years, high-density planting, lack of light, and niches that are not conducive to drainage, ventilation and cooling.

[prevention and control measures] in mild disease areas, comprehensive prevention and treatment should be emphasized. In seriously ill areas, chemical prevention and control should be generally adopted to control hazards and epidemics.

Prevention and control of seedling raising technology. Select the lower altitude area of Zhongshan belt to establish a regular nursery. Strict control of planting density, suitable time seedlings, fixed seedlings, elimination of weak seedlings and diseased seedlings. Change the bed in time, graded transplantation, enhance the light. In the period of putting leaves and new shoots, take measures such as covering the curtain to prevent late frost. Appropriate amount, timely application of chemical fertilizers, growth promoters, herbicides, but to prevent burns. Dredge channels and drains in autumn, remove weeds and other obstacles, and drive ice to remove silt in early spring. For small nurseries with insufficient medical equipment, young seedlings can use seedbeds to build snow sheds to prevent diseases.

Forest management technology prevention and control. Combined with site renewal, do a good job of forest clearance and land preparation before afforestation. Select qualified strong seedlings for afforestation and replanting. Seedlings, false planting, planting and other operations should pay attention to protect the seedlings and maintain the vitality of the seedlings. Strengthen the tending of young forests, timely support seedlings, cultivate soil, weed, cut irrigation, clean up the collapsed gravel and other obstacles around the plant, to prevent the plant from being pressed or lodged.

Chemical control. Before snow cover in early winter (early and middle October in nursery, late September to early October in woodland), fungicides with broad spectrum, long efficacy, strong internal absorption and adsorption were used. Such as 20% trimethoprim EC (1.5~4.5kg/ha), 70% methyl topiramate (3.0~9.0kg/ha), 25% carbendazim or 40% polysulfide mixture, duofu mixture (9~12kg/ha) and so on. The best control effect can be achieved by using electric hand-held ultra-low capacity sprayer, diluting the pesticide 5 times 10 times and spraying once, which is especially suitable for working in mountainous areas and in the early winter with changeable climate. The prevention and control of young forest uses carbendazim gel suspension, powder cream EC and so on, which can be sprayed with the original solution.