Nghe An mountainous district has over 200 hectares of corn devastated by fall armyworms.

Many corn fields at the 3-10 leaf stage in Nghia Hoan, Tan Phu, Nghia Thai communes... of Tan Ky district are being devastated by fall armyworms, unable to grow.

Mr. Quang's family in Lam Xuan hamlet, Nghia Hoan commune has more than 1 sao of corn in the 10-leaf stage. However, unlike last year, this year the corn was damaged by fall armyworms to the point of losing all its leaves. Although Mr. Quang's family has sprayed pesticides twice, it has not been effective. He said that when he personally pulled the corn stalks apart, he still saw many worms still alive. The surrounding corn fields also had similar symptoms.

Fall armyworms are often found in corn shoots, so farmers must spray from top to bottom to be effective. Photo: Xuan Hoang

Mr. Nguyen Thanh Phuong - Chairman of Nghia Hoan Commune People's Committee said that the locality has 33 hectares of corn, of which 26.5 hectares are infected with fall armyworm. The corn areas that are not infected with fall armyworm are because people grow genetically modified corn varieties.

According to data from the Plant Protection and Cultivation Station of Tan Ky district, the entire district has more than 691 hectares of autumn-winter corn, but over 550 hectares are infected with fall armyworm, of which nearly 200 hectares are severely infected. Localities with corn areas infected with fall armyworm include: Nghia Hoan 26.5 hectares, Nghia Phuc 195 hectares, Phu Son 40 hectares, Tan An 20 hectares...

Staff of the Tan Ky District Plant Protection Station instruct farmers on how to detect fall armyworms on corn plants. Photo: Xuan Hoang

Corn varieties severely damaged by fall armyworm are: L14, CP111, LVN10, CP3Q, NK4300, DK6919... Areas less affected by fall armyworm are transgenic corn varieties.

Faced with the above situation, the District Plant Protection and Cultivation Station coordinated with the District Agricultural Extension Station to open 8 training classes for farmers on how to detect worms and spray chemicals to kill this type of worm, but the fall armyworm continues to damage corn plants.

Characteristics of fall armyworm:Larvae have 6 instars, instar 1 - 2 the body is light green - light yellow is common. When larvae develop instar 3 - 6 they are grayish brown - dark brown with vertical stripes on the body. Instar 1 larvae are about 0.5 mm long, instar 3 larvae are 6 - 9 mm long; instar 6 larvae are 30 - 40 mm long.

On the forehead of the adult larvae, an inverted yellow Y shape is clearly visible, the dorsal surface is black with long, stiff hairs. On the dorsal surface, the last abdominal segment has 4 black spots arranged in a square.

Symptoms of corn plants damaged by fall armyworm:1st and 2nd instar larvae feed on the epidermis on the underside of young leaves, causing characteristic white square or rectangular marks. Older larvae feed on the leaves and leaf sheaths, creating large holes.

Prevention:Regularly check the fields, especially at the 3-6 leaf stage of corn to detect egg nests, remove and destroy them. Use ash or diluted soap water to pour on the corn cobs to kill the larvae. Clean the weeds around the corn garden to limit the hiding places of the worms. Prepare the soil and let it dry so that the larvae and pupae in the soil die or are easily destroyed by natural enemies.

Use active ingredients of pesticides allowed for use according to the instructions of the agricultural extension service to spray when the majority of worms are 1-3 instars (corn stage 3-6 leaves), spray early in the morning or cool afternoon. Use pesticides according to the "4 rights" principle.

Light and bait traps can be used, using yellow sticky traps with sex pheromones, sweet and sour bait traps or light traps to kill adult worms.