Barrett A. Courville | 4/6/2011 11:20:54 PM
Today I want to review three of our minor rice insect problems that can occur each year, the rice seed midge, rice leafminer and aphids. Listed below are descriptions of the three insect pests.
Rice Seed Midge
Adult midges resemble small mosquitoes and swarm over rice fields, rice levees, roadside ditches and other bodies of water. Elongated eggs are laid on the surface of open water in strings. Larvae live on the bottom of flooded rice fields in spaghetti-like tubes. Larvae injure rice by feeding on the embryo of germinating seeds or on the developing roots and seeds of very young seedlings. Midge injury occurs in water-seeded rice and is usually not important once seedlings are several inches tall. The potential for midge injury increases when fields are flooded far in advance of water-seeding rice. Water-seeded fields should be scouted for midge injury, checking for hollowed out seed within five to seven days after seeding. Injury from the midge can be insignificant (not economically important) to very severe. Injury can also be localized, making damage assessment difficult. In some instances, whole fields may need to be replanted. In other instances, only parts of fields may require reseeding. Monitor fields until rice seedlings are several inches tall.
Rice Leaf Miner
Adult flies are less than 1/4-inch long, with a metallic blue-green to gray thorax and clear wings, and they lay eggs on rice leaves as they lie on the water. The larvae are transparent to cream-colored after hatching but become yellow to light green within a few days. Larvae tunnel between the layers of the leaf, attacking and killing leaves closest to the water. Larvae move up the plant, killing additional leaves, and, under heavy infestations, the entire plant may die.
Rice is attacked in the early spring, and infestations usually occur on the upper side of levees where water is deepest. Leaf miner problems are more severe in continuously flooded rice than in periodically flooded rice. Leaf miners appear to attack rice fields in the same vicinity from one year to the next.
Scout for rice leaf miner larvae by pulling a rice leaf gently between the thumb and forefinger. If larvae or pupae are there, a bump can be felt in the leaf blade. The larvae or pupae can be found by separating the layers of the leaf. If plant populations are being reduced to less than optimum stands (10- 15 plants per square foot), chemical control may be necessary.
Some years we also will see aphids feeding on the seedling rice plants. They have been identified as bird cherry oat aphids. They are small insects that produce toxic saliva that can cause stunting or death of small seedling rice. Most of the time, after the field is flushed or flooded and the weather warms up, there is no need for treatment.