Eggs are stacked together to egg masses that look like a moldy soybean covered with brown scale-hair (Fig 1). Female adults have triangle wings with one obvious black spot in the center (Fig 2). Male adults have grayish brown wings with one dark brown twill and 7 to 9 small black specks aside the outer edge.
The larvae bore a small hole on rice stem. Most obvious are dead hearts or dead tillers that can be easily pulled from the base during the vegetative stages. There is no frass outside the hole but there is fine white frass inside the stem (or the larva itself, Fig 3). Whiteheads occur during reproductive stage where the emerging panicles are whitish and unfilled or empty (Fig 4).
Economic importance and control methods
Cultural control: harvest fields at ground level to remove the larvae in stubbles, burn or destroy stubbles before winter if machine-harvested. Keep deep water during winter in fallow fields or flood the fields before plowing in early spring. Adjust rice growing to avoid mixed-stage rice plants and to reduce bridging fields. Egg masses may be removed by hand before transplanting. Application of nitrogen fertilizer should be split following the recommended rate and time of application.
Biocontrol: Release of Trichogramma during adult population peaks, 40,000 wasps per acre per release (100,000 per ha), 3 releases in total during tillering and early booting stage. An additional small scale release could be appropriate at the seedbed stage. For timing of release consider available information on stages present in the field and start releasing Trichogramma when adults/egg masses are observed.
Chemical control: if needed and Trichogramma cards are not available, a pesticide may be used according to the label instruction (see green and yellow list for details). The action threshold is >2 egg masses/20 hills at tillering stage and >1 egg mass/20 hills after panicle initiation.
*the information provided on this page should also be considered for striped- and pink stem borer, however, appearance of adult moth’s, eggs and larvae is a bit different.