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Grafting prevention and control of chestnuts
The cross-winged moth is a serious threat to grafted chestnut cultivation. As the area under chestnut grafting continues to expand, the damage caused by this pest is becoming more severe. This not only reduces chestnut yields but also significantly discourages farmers from investing in the chestnut industry.
1. Symptoms of Damage by Cross-Winged Moth
The larvae of the cross-winged moth typically bore between the phloem and xylem of the trunk, creating irregular tunnels. Brown frass (insect excrement) accumulates within these tunnels and at the graft union. The affected bark swells, cracks, and becomes heavily damaged by feeding activity. In winter, the grafted tree may fail to produce new shoots, leading to graft failure. If the graft site is located low on the trunk, the entire plant can die.
2. Life Cycle and Habits
In the Dandong region, the cross-winged moth completes one generation per year. The second instar larvae overwinter beneath the bark of infested trees. They begin feeding in late April to early May and reach the larval stage in late May to late June. Once mature, the larvae create round emergence holes about 5–6 mm in diameter on the trunk bark. These holes are often filled with wood shavings and feces. The timing of these holes varies depending on where the larvae are feeding—sun-exposed areas tend to show symptoms about half a month earlier than shaded ones, while the middle and lower parts of the trunk develop signs earlier than the upper sections. The larval stage lasts from mid-July to late July, lasting approximately 20–25 days. By mid-August, adults begin to emerge and lay eggs on rough bark surfaces, wounds, or existing holes. Egg-laying occurs in late August, with an egg incubation period of around 10 days. Larvae hatch from late August to mid-October.
3. Control Methods
(1) Agricultural Control
During the larval hatching period, the rough bark below the graft union of older trees can be carefully cut away using a knife and burned in a concentrated manner to destroy both larvae and eggs. After scraping the bark, insecticides should be applied again. When adult moths emerge, black light traps can be used effectively. Additionally, better management of chestnut trees can improve their overall health and reduce the risk of injury. Improving grafting techniques, such as avoiding "pressing the lid" and directly covering the graft with plastic strips, helps prevent moisture buildup. When the buds grow to 3–5 cm, the bags should be removed, keeping the graft area clean and well-ventilated to minimize infestation.
(2) Chemical Control
From late May to late June, when grafted branches reach 30–40 cm in length, it is a critical time for larval activity. At this stage, spraying the graft junctions and trunks with insecticides is highly effective. Commonly used agents include 20% fenvalerate emulsifiable concentrate diluted at 1000 times, 30% peach Xiaoling EC diluted at 1500 times, and 2.5% deltamethrin EC diluted at 1500 times. Timely application during this period can significantly reduce infestation. After the graft heals within 1–2 years, the damage will decrease substantially, and the pest will no longer pose a serious threat to grafted chestnut trees.