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A Detailed Guide to the Occurrence and Control of Spruce Red Blight

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In recent years, with the increase in the number of spruce plantings, spruce red blight has occurred severely, reaching as high as 50% in some dense forest belts, seriously weakening tree vigor and even causing tree death. The disease strikes swiftly, developing from the lower part of the tree to the upper part, from the outer edge of the crown toward the inner part, and from the base of the compound leaves toward the tip. In as little as 1 week, or at most 10 days, it can cause the leaves of the entire plant to turn yellow and then drop. The disease is caused by fungi. When temperature changes abruptly and humidity increases, the tree becomes diseased. Diseased leaves first develop small brown spots, which then expand and turn dark brown; when it rains and is humid,

In recent years, with the increase in the number of spruce plantings, spruce red blight has occurred severely, reaching as high as 50% in some dense forest belts, seriously weakening tree vigor and even causing tree death. The disease strikes swiftly, developing from the lower part of the tree to the upper part, from the outer edge of the crown toward the inner part, and from the base of the compound leaves toward the tip. In as little as 1 week, or at most 10 days, it can cause the leaves of the entire plant to turn yellow and then drop.

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

Control methods: Follow "prevention first, scientific control," strengthen management, protect the roots and nourish the leaves, enhance resistance, and strengthen tree vigor. Select varieties with strong disease resistance, such as green-type Keteleeria (Keteleeria spp.). The soil should be a plot with medium fertility, and soil with good permeability should be chosen. Fertilize reasonably, and do not damage conducting roots with a thickness of 0.3 cm or more. Cultivate reasonably and irrigate promptly. 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 both root drenching and spraying simultaneously gives good results. Spraying is done before spruce buds break and when sap begins to flow, spraying 5 degrees Baume lime sulfur mixture. In early May and August, alternately spray a mixture of 50% Yisheng at 600 times dilution plus Zengxiaowang, 70% thiophanate-methyl at 1000 times dilution, plus a botanical biological fungicide at 600 times dilution, once every 5 days, for a total of 2 sprays. Root drenching is done after the tree produces new leaves and after growth stops, alternately drenching the roots with 55% dexon at 700 times dilution and 50% Jinxiaokang at 1000 times dilution, once every 3 days, for a total of 2 times. When the above agents are used as preventive treatment, the amounts can be halved. To control the disease, deeply bury or burn the leaves that have already withered and turned yellow.

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