Chestnut gall wasps need targeted control this year, and chestnut growers should pay attention

The chestnut gall wasp, also known as the chestnut tumor wasp, is a major insect pest damaging chestnut trees. It occurs almost every year in chestnut-producing areas in China, but this year the outbreak is especially severe. Large trees, especially old unpruned trees, have reached a 100% damage rate. Controlling the chestnut gall wasp brooks no delay.

The chestnut gall wasp has one generation per year and overwinters as first-instar larvae inside infested chestnut buds. In the Yanshan mountainous area, overwintering larvae begin to move and feed during the bud-break period in mid-April and grow rapidly. In early May, during the shoot-sprouting and leaf-unfolding period, galls begin to form. The galls are mostly at the tips of new shoots or on the main veins and petioles of leaves. Feeding activity generally lasts about 50 days, and by mid-May they gradually age. Pupae begin to appear in late May, with the peak in early June, and pupation ends in early July. The pupal stage lasts about 15 days. The adult emergence period runs from early June to mid-July, with the peak from late June to early July. After emerging, adults do not leave the gall and remain inside the gall for about 11 days. They exit the gall from mid-June to late July, with the peak exit period in early July. Outside the gall, adults live an average of 3.1 days, with a maximum of 5.5 days. Adults are not strong fliers; they mostly crawl among branches and leaves, are active during the day, and rest on the undersides of leaves at night. They have no phototactic or supplementary feeding habits. Adults can lay eggs after exiting the gall, laying 2 to 4 eggs each time, and each female can lay about 200 eggs. The egg-laying period is about 30 days. Eggs begin to hatch in mid-July, all hatch by early September, and small larvae begin to overwinter in early October.

Control methods: Prune out galls at the right time. Before adult emergence, remove gall-infested branches along with pruning, which can both improve crown ventilation and light penetration and reduce the pest source. In winter, cut off all parts of one-year-old branches above the dormant buds. Results can be restored after one year. Large branches can also be cut back, waiting for new shoots to sprout and rejuvenate the tree vigor. For chestnut trees with severe damage and a sharp drop in fruiting, short-cut renewal can be carried out. In early July, during the peak period when adult chestnut gall wasps exit the galls, spray the crown with 80% dichlorvos at 1000 times dilution or bromo-cypermethrin at 1000 times dilution, once every 7 to 10 days, for two consecutive sprays.