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What are the control methods for spruce red blight?

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In recent years, with the increase in the number of spruce plantings, spruce red blight has become severe, reaching up to 50% in some dense forest belts, seriously weakening tree vigor and even causing tree death. The disease develops rapidly, spreading from the lower part of the tree to the upper part, from the outer edge of the crown inward, and from the base of the compound leaves to the tip. In as many as 10 days, or as few as 1 week, the entire tree's leaves can turn yellow and then fall off. The disease is caused by fungi. When temperature changes abruptly and humidity increases, the tree shows symptoms. Diseased leaves first develop small brown spots, which later expand and turn dark brown; when wet from rain, the lesions produce

In recent years, with the increase in the number of spruce plantings, spruce red blight has become severe, reaching up to 50% in some dense forest belts, seriously weakening tree vigor and even causing tree death. The disease develops rapidly, spreading from the lower part of the tree to the upper part, from the outer edge of the crown inward, and from the base of the compound leaves to the tip. In as many as 10 days, or as few as 1 week, the entire tree's leaves can turn yellow and then fall off.

The disease is caused by fungi. When temperature changes abruptly and humidity increases, the tree shows symptoms. Diseased leaves first develop small brown spots, which later expand and turn dark brown; when wet from rain, the lesions produce many raised small black mold spots, which are the fungal stroma and the conidiophores and conidia borne on it. It can spread by wind and rain to the bark of the main trunk, directly infecting the green main stem or spreading from small branches and leaves to the green main stem, forming brown, reddish-brown slightly sunken canker spots. After these spots develop and encircle the stem for 1 full turn, the upper part dies completely. Sometimes the canker spots on the main stem do not expand quickly but do not heal either; as the main trunk grows, they gradually become embedded in the trunk, forming groove-like diseased areas. Although the tree does not die, it is prone to wind breakage.

Control methods: follow "prevention first, scientific control", strengthen management, protect roots and nourish leaves, enhance resistance, and strengthen tree vigor. Select varieties with strong disease resistance, such as the green-type Keteleeria (Keteleeria spp.). Choose plots with medium soil fertility and select soil with good permeability. Fertilize reasonably and do not damage conducting roots with a diameter of 0.3 cm or more. Cultivate reasonably and irrigate in a timely manner. In high-temperature seasons, avoid cultivation as much as possible to prevent root damage. In high-temperature seasons, do not irrigate between 11:00 and 14:00.

Using chemical control with root irrigation and spraying simultaneously gives good results. For spraying, before spruce buds break and when sap begins to flow, spray 5 degrees Baume lime sulfur mixture. In early May and August, alternately spray a mixture of 600-fold dilution of 50% Yisheng plus Zengxiao Wang, 1000-fold dilution of 70% thiophanate-methyl, and 600-fold dilution of a plant-derived biological fungicide, once every 5 days, for a total of 2 sprays. Root irrigation is done after the tree produces new leaves and after growth stops, using 700-fold dilution of 55% dexon and 1000-fold dilution of 50% Jinxiaokang alternately for root irrigation, once every 3 days, for a total of 2 times. When the above agents are used as preventive treatment, the amount can be halved. To control the disease, deeply bury or burn the already yellowed and withered diseased leaves.

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