Walnut Leaf Webber Pest: Symptom Identification and Control Methods

  1. Distribution and damage symptoms. It is a major leaf-eating pest of walnut, distributed in North China, Northwest China and Central-South China. The larvae bite and feed on walnut leaves, and when outbreaks are severe they can strip all the leaves from the entire tree.

  2. Morphological characteristics and life habits. It belongs to the order Lepidoptera, family Pyralidae, also known as the wood webworm, and the leaf-webber pyralid.

  (1) Adult. Body length 14~20 mm, wingspan 35~50 mm, the whole body yellowish brown. The forewings are darker in color, the hindwings grayish brown, becoming darker toward the outer margin.

  (2) Egg. Spherical, densely arranged in a fish-scale pattern.

  (3) Larva. Mature larva body length 20~30 mm, head black and glossy, pronotal plate black with 6 yellowish-white spots on the front margin, the dorsal midline broad and apricot yellow, each body segment on the sides with yellowish-white spots, the ventral surface of the abdomen yellowish brown with a small amount of short hair.

  (4) Pupa. About 16 mm long, dark brown to black.

  (5) Cocoon. Dark brown, flat oval, about 20 mm long and about 10 mm wide.

  It occurs 1 generation per year, with the adult period from late June to early August. Eggs are laid on the leaf surface and hatch in early July; late July to early August is the peak damage period. The larvae live in groups, spin silk and form webs on the leaf surface, binding leaves together and rolling them into a tube shape; the larvae feed inside and deposit their frass there, which finally forms a mass as the larvae grow larger. After the 4th instar, the larvae disperse to cause damage. The larvae feed, move and relocate at night, and rest quietly inside the damaged leaves during the day, and from August to September they overwinter in the soil as mature larvae.

⟦NL>   3. Control methods

  ① Manual capture and killing. Taking advantage of the gregarious habit of the larvae when damaging leaves, the insect nests can be picked off and burned in a centralized manner to kill the insects.

  ② Digging out cocoons. The cocoons are generally concentrated in the soft soil beside the tree roots. Before the soil freezes in autumn or after it thaws in spring, dig out the cocoons and burn them in a centralized manner.

  ③ Chemical control. In mid-to-late July, at the early stage of larval damage, spray 25% Kung Fu emulsifiable concentrate at 1000 times dilution, or 40% chlorpyrifos emulsifiable concentrate at 800~1000 times dilution, or 40% dimethoate emulsifiable concentrate at 2000 times dilution, or 25% carbaryl wettable powder at 500~800 times dilution.