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Symptoms of Spruce Snow Mold and Its Control Methods

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Spruce snow mold is mainly distributed in some countries north of 40 degrees north latitude, where it damages tree species such as Japanese cedar, fir and spruce. In China, this disease has only been found damaging **spruce. Symptoms: after the above-ground parts of the whole plant and the needles are infected under the snow, they are covered with a grayish-brown mycelial layer, or the mycelium invades the interior of the host, causing the tree to become moldy and rot and to suffocate. In mild cases, the mycelial layer is cottony; in severe cases, it is felt-like. Its color is brown in the early stage, and white and grayish-brown when the snow is about to melt. When the disease is mild, the damage is distributed in clumps. When severe, the trees fall over in rows.

Spruce snow mold is mainly distributed in some countries north of 40 degrees north latitude, where it damages tree species such as Japanese cedar, fir and spruce. In China, this disease has only been found damaging **spruce.

Symptoms: after the above-ground parts of the whole plant and the needles are infected under the snow, they are covered with a grayish-brown mycelial layer, or the mycelium invades the interior of the host, causing the tree to become moldy and rot and to suffocate. In mild cases, the mycelial layer is cottony; in severe cases, it is felt-like. Its color is brown in the early stage, and white and grayish-brown when the snow is about to melt. When the disease is mild, the damage is distributed in clumps. When severe, the trees fall over in rows. After the snow melts, the diseased needles fall off, the bark tissue of the tree trunk ulcerates and rots, and the tree gradually dies.

Pathogen: The pathogens are Botrytis cinerea Pers. (BotrytiscinereaPers.), Sclerotinia sclerotiorum (Lib.) de Bary (Sclerotiniadsclerotiorum(Lib.)deBary) and Truncatella sp. (Truncatellasp.).

Disease pattern: Early winter and early spring are the main periods of disease occurrence, and it spreads rapidly in early spring. The common characteristics of the three pathogens such as Botrytis cinerea are: from 0-22°C, the growth rate increases as the temperature rises; above 28°C, growth is extremely slow and gradually stops; below 22°C, vegetative growth is vigorous. Mature sclerotia generally have no dormancy period. These pathogens are weak parasites. When trees suffer freezing injury, sunscald and various other natural and human-caused injuries, as well as insufficient light, poor drainage and extensive management, the disease will be aggravated.

Control: 1) Strengthen tree management, plant at a reasonable density, and improve the disease resistance of the seedlings. 2) Before snow cover in early winter, spray 20% dinocap EC, 20% thiophanate-methyl, 25% carbendazim or 40% lime sulfur mixture and other agents for control.

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