When is the control time for rice stem borers?

Rice stem borers bore into the rice stems as larvae to feed, posing a huge threat to rice. When is the control time for rice stem borers?

1. Control time for rice stem borers

The control time for rice stem borers must be determined according to the pest situation and the seedling condition. Chemical control should be carried out from the peak of egg hatching to before the occurrence of first-instar larvae. The specific time should be based on the information from the local plant protection station.

2. Characteristics of rice stem borers

1. Sesamia inferens (purple stem borer)

Sesamia inferens is distributed in all rice regions of China, with heavier occurrence south of the Yangtze River. Its hosts include rice, wheat, corn, wild rice stem, broad bean, rapeseed and so on.

When mature, the larva of Sesamia inferens is stout, with a body length of 20-30 mm, a red-brown head and a purplish-red back.

The adult is 12-15 mm long with a wingspan of 27-30 mm. Its body is stout, and the female moth is somewhat larger. The head and thorax are grayish brown, the abdomen is light brown, and the forewings are nearly rectangular and light grayish brown with a darker outer margin. There is a dark brown line from the wing base to the outer margin.

The pupa of Sesamia inferens is rather stout and yellow-brown, with a length of 13-18 mm, and the head and thorax have a white powdery secretion.

The eggs of Sesamia inferens are oval and brown, with longitudinal and transverse striations on the surface. The eggs are mostly laid inside the leaf sheath, generally in 2-3 rows, with a dozen or so clustered together.

2. Chilo suppressalis (striped stem borer)

Chilo suppressalis has a relatively wide distribution range, from Heilongjiang in the north to Hainan Island in the south, and it commonly occurs in rice regions throughout northern and southern China. It damages not only rice but also wild rice stem, corn, broad bean, rapeseed and so on.

The mature larva of Chilo suppressalis is relatively large, with a body length of 20-30 mm, a red-brown head and a light brown body, with 5 brown stripes on the back.

The adult is 10-15 mm long and grayish yellow-brown. The forewings of the female moth are nearly rectangular, with 7 small black spots on the outer margin. The male moth is slightly smaller than the female moth, and its body color and wing color are both darker.

The pupa of Chilo suppressalis is 11-17 mm long, cylindrical and brown. In the early stage, 5 dark brown longitudinal lines can be seen on the back.

The eggs of Chilo suppressalis are flat and oval, about 1.2 mm long, with dozens or even hundreds of eggs stuck together.

3. Scirpophaga incertulas (yellow stem borer)

Scirpophaga incertulas is mainly distributed in the rice regions of the Yangtze River basin and south of it, with scattered distribution as far north as Yantai.

The larva of Scirpophaga incertulas is 14-20 mm long, pale yellow-white, with a yellow-brown or light brown head.

The adult of Scirpophaga incertulas is 8-13 mm long. The forewings are long triangular. The female is relatively large, pale yellow overall, with an obvious small black spot in the center of each forewing and a tuft of yellow-brown fuzz at the end of the abdomen. The male is relatively small, pale grayish brown overall, also with an obvious small black spot in the center of each forewing, and there is also a dark brown oblique line from the wing tip to the center of the wing.

The pupa of Scirpophaga incertulas is long cylindrical, greenish white, and turns brown when about to emerge; the pupa is 10-15 mm long.

The eggs of Scirpophaga incertulas are flat and oblong, waxy yellow, in masses, with each mass containing dozens or even hundreds of eggs, covered with yellow-brown fuzz.

Scirpophaga incertulas has a very specialized feeding habit and feeds only on rice. The damage caused by its larvae runs through the entire growth period of rice. In the seedling stage and tillering stage, it easily causes deadheart seedlings; in the booting stage, it causes dead booting; and in the heading stage, it can cause white heads.

3. Control of rice stem borers

1. In terms of the cultivation system, change the coexistence of single-cropping and double-cropping rice to large-area double-cropping rice or single-cropping rice, and try to eliminate the “bridge fields” that favor the survival of stem borers. Transplant rice seedlings at the proper time and manage them reasonably so that the peak occurrence period of stem borers is staggered from the tillering stage and booting stage of rice.

2. During winter and spring, remove weeds along the field edges to eliminate larvae and pupae overwintering among them. Before the peak hatching of eggs, remove barnyardgrass and weeds along the field edges.

3. The pupation period of stem borers is generally in the spring plowing production season, at which time spring plowing and field soaking should be carried out in time. Plow rice stubble, rice straw, weeds and so on into the soil so as to eliminate overwintering larvae and reduce the pest population base.

4. At the same time, physical control methods should be adopted, using light, high temperature or obstacles and other means to kill or hinder pests. The relatively mature physical control method used in production is light trapping to kill adults. The adults of rice stem borers have a strong tendency toward the light emitted by black light lamps and frequency vibration insect-killing lamps. During the peak occurrence period of adults, black light lamps or frequency vibration insect-killing lamps can be used to trap and kill large numbers of adults, thereby reducing the number of eggs laid by adults and achieving a very good preventive effect.

5. Chemical control. According to the different characteristics of Sesamia inferens, Chilo suppressalis and Scirpophaga incertulas, choose different pesticides for control.

To control Sesamia inferens, when deadheart damage symptoms are found during the seedling stage, spray pesticide in time. The pesticide can be 18% dimehypo aqueous solution at 200 ml per mu, diluted with 50 kg of water for spraying. Spray once every 5-7 days, and generally 2-3 treatments are enough. During the rice jointing stage, use 40% imidacloprid at 100 g/mu, diluted with 50 kg of water for spraying. From the booting stage to the heading stage, use 200-250 ml of dimehypo aqueous solution per mu, diluted with 50 kg of water for spraying, which can achieve an ideal control effect.

To control Chilo suppressalis, when deadheart seedlings caused by Chilo suppressalis damage are found during the seedling stage, 25% dimehypo at 100-150 g/mu can be used at the seedling stage, diluted with 50 kg of water for control. At the white head stage, use 100-150 g of 50% dimethoate emulsifiable concentrate per mu, diluted with 50 kg of water for spraying, which has a very good insecticidal and ovicidal effect.

For Scirpophaga incertulas, at the peak of egg hatching and at the stage of breaking the boot and exposing the panicle, use 5% fipronil at 15 ml/mu, diluted with 50 kg of water for spraying, which can effectively prevent deadheart seedlings and white heads.

Rice stem borer eggs hatch relatively quickly, and the timing differs among generations and is also affected by region and temperature. Therefore, for the control time, it is best to consult the relevant departments.