Key points for the control of the yellow cutworm

1. Morphological characteristics

Adult: body length 14~19 mm, wingspan 32~34 mm. Body yellowish brown or grayish brown. Forewings grayish yellow, the transverse lines on the wing surface are not obvious, but the kidney-shaped mark, ring-shaped mark and rod-shaped mark are clear. The center and outer margin of the wing are dark brown. Hindwings white, with the anterior margin slightly yellowish brown.

Egg: hemispherical, about 0.5 mm in diameter. The eggshell surface has 16~20 longitudinal ridge lines.

Larva: mature larva body length 33~43 mm. Yellowish brown, glossy. The body surface is much wrinkled, with inconspicuous granules. The anal plate is divided by a central yellow longitudinal stripe into 2 large yellowish brown patches.

Pupa: body length 15~20 mm. There are sparse and inconspicuous punctures in the center of the dorsal side of the fourth abdominal segment.

2. Occurrence pattern

The yellow cutworm overwinters as larvae and a small number of pupae in host fields and weed patches. The overwintering larvae pupate in mid-March of the following spring, and begin to emerge as adults in early April. The peak period of moth and egg occurrence is in early to mid-May, and the peak hatching period of eggs is in mid-May. Late May to early June is the peak damage period of the larvae. The moth peak periods of subsequent generations appear in mid-July, mid-September and late October respectively.

Adults have strong phototaxis. Female moths mostly lay eggs on root stubble, grass stalks and the leaves of various weeds on the soil surface, often in strings of dozens of eggs. The larvae hide by day and come out at night. Newly hatched larvae feed on the tender leaves and growing points of host seedlings. Larvae of the 1st~2nd instars bite small holes or notches, and after the 3rd instar they mostly feed on the stem base in the surface soil layer, and can bite off tender stems or bite the base of thicker stems into incomplete shapes. When the damage is severe, a large number of seedling stems are bitten off or the stem bases are incomplete, causing them to wilt and die. Sometimes some larvae can also climb to the top of the seedlings to feed and bite off the tender tips.

The damage degree of the first-generation larvae of the yellow cutworm is related to the overwintering population base and the instar of the overwintering larvae. If the number of overwintering late-instar larvae is large, the number of adults in the following spring will also be large, and the damage by the first-generation larvae will be severe. The yellow cutworm is not tolerant of high temperatures. The occurrence period of the second generation coincides with the hot summer season, so the occurrence is often relatively small. In North China and East China, in general years, the damage is mainly caused by the first-generation larvae. This insect has relatively low requirements for rainwater and humidity, so the damage is more severe in the arid and rain-deficient northwest region.