Stem borers
Stem borers cause the worst damage, as they infest rice plants from the seedling stage to maturity, including:
1. Damage on young plants during early and later tillering. Caterpillars enter the leaf sheath and the young stem from the bottom, causing the death of the stem: such damage is often called ‘dead heart’.
2. Damage to the panicle, causing ‘white panicles’. The young caterpillars (mostly from the second generation) gather a few centimeters below the panicle inside the flower stalk, which then dries up entirely. According to the timing of attack, it becomes either a completely white or a dried panicle, which may eventually break.
Apart from these two visible cases, any attack on the stem is just as harmful. If the insect attacks when the plant has already reached an advanced stage of development, the older caterpillar embeds itself in the lower parts of the stem and reduces or even stops the nourishment of the panicle. Damage then shows through the drying of some of the spikelets, leading to a decrease in the number of grains at harvest. This effect, which is far less visible, reduces the weight of the harvest and can only be measured by weighing the harvest.