Pest Library

Stem borers can destroy rice at any stage of the plant from seedling to panicle initiation. They feed upon tillers and causes dead heart or drying of the central tiller, during vegetative stage; and causes white ear heads at reproductive stage.

Identification of insect pest:

• Eggs: are creamy white, flattened, oval and scale like and laid in mass and covered with buff-coloured hairs.
• Larva: Pale yellow with dark brown head.
• Pupa: White silken cocoons are found inside the stem.
• Adult:
• Female moth: Bright yellowish brown; forewings with a black spot.
• Male moth: Smaller with pale yellow; forewings without black spot.

The rice yellow stem borer is the most common species in tropical wetland areas and is a major pest of tropical lowland and deep-water rice. It attacks all stages of the crop. Eggs are laid on upper surface (and upper half) of leaves in groups (average about 80) covered in tan scales from the female. Eggs hatch in 5-10 days, and the white larvae bore into the leaf sheath resulting in yellowish-white patches. Later, they invade the stem and cause dead hearts or drying up of the central shoots (at the vegetative stage), and whiteheads (at the panicle stage). When fully grown (20-40 days) the larvae are pale-yellow to yellowish green with a brown head, up to 20 mm long. They pupate in white silk cocoons made in hollow stems at the base of the plant. In deep-water rice, the larvae and pupae may be beneath the water.

The larvae become dormant if dry periods occur or in seasons when rice is not grown. During rice-free times, the larvae remain in the stubble below the soil. Mortality is high (90%) during periods of dormancy, due to destruction of stubble, and possibly due to predation (spiders) and adverse environments (droughts). The female moth has pale-yellow or light-brown forewings, each with a characteristic single, black spot. The smaller grey or light-brown male has two rows of small spots at the tip of each forewing. Females are 13 mm long with 32 mm wingspans. Spread over short distances occurs as eggs on infested seedlings used for planting; as larvae that crawl from plant to plant and disperse on silken threads blown by the wind, as pupae in harvested stems and adults on the wing at night. High nitrogenous field favours population buildup of the stem borers. Fields planted later favour more damage by the insect pest as compared to earlier planted fields. Stubble that remains in the field can harbour stem borer larvae and or pupae.

How to identify Check the field for the following damage symptoms:

• Dead hearts or dead tiller that can be easily pulled from the base during the vegetative stages.
• Tiny holes on the stems and tillers.
• Whiteheads during reproductive stage where the emerging panicles are whitish and unfilled or empty.

• Frass or faecal matters inside the damaged stems.
• Dead hearts and whiteheads symptoms may sometimes be confused with damages caused by rats, neck blast, and black bug diseases. To confirm stem borer damage, visually inspect rice crop for dead hearts in the vegetative stages and whiteheads in reproductive stages. Stems can be pulled and dissected for larvae and pupae for confirmation of stem borer damage.

• Use resistant varieties. Contact your local agriculture office for up-to-date lists of varieties available.
• At seedbed and transplanting, handpick and destroy egg masses.
• Raise level of irrigation water periodically to submerge the eggs deposited on the lower parts of the plant.
• Before transplanting, cut the leaf-top to reduce carryover of eggs from the seedbed to the field.
• Ensure proper timing of planting and synchronous planting, harvest crops at ground level to remove the larvae in stubble, remove stubble and volunteer rice, plough and flood the field.
• Install light trap @ 1/ha and pheromone trap @ 5/acre.
• Release of egg parasitoid Trichogramma japonicum @ 2cc per acre 3 times at weekly intervals.
• Apply nitrogen fertilizer in split following the recommended rate and time of application.
• Parijat products-Mortel SC @ 400-600 ml /acre, Mortel GR @ 6.5-10 kg/acre, Ambivi @ 2.5 kg/ acre and Corato @ 4 kg/acre.