Midges are flies in the family Chironomidae. Many species of midges inhabit rice fields, often present in large numbers, but probably only a few species are pests.
Adult midges can be seen in swarms over rice fields, levees, roadside ditches and other bodies of water. Adult midges resemble small mosquitoes but lack needle-like mouthparts and do not bite. Eggs are usually laid on the surface of open water.
After emerging, the larvae move to the soil surface, where they live in spaghetti-like tubes constructed from secreted silk, plant debris and algae.
Larvae are often red in color. The larvae mature through four instars before pupating under water in the tubes. The life cycle from egg to adult requires 10-15 days.
Midge larvae feed 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 more than two to four inches tall. The potential for midge injury increases when fields are flooded far in advance of water-seeding because this increases the chances that midges will lay their eggs in the field.
Signs Of Midge Feeding
Water-seeded fields should be scouted for midge injury within five to seven days of seeding. The presence of larval tubes indicate that midges are in the field.
However, because most midge species do not attack rice, the rice farmer must check for signs of midge feeding. These include chewing marks on the seed, roots and shoots and hollow seeds.
If midge injury is present and plant stand has been reduced to fewer than 15 plants per square foot, treatment may be necessary. 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.
Reduce Damage Potential
Rice seed midge management includes chemical and cultural control options. One cultural management option is to drain fields to reduce numbers of midge larvae.
Re-seeding of heavily infested fields may be necessary.
The potential for damaging levels of seed midge can be reduced or prevented by using recommended water and crop management practices. Holding water in rice fields for more than two to three days before seeding encourages the buildup of large midge numbers before seeding and should be avoided.
Practices that encourage rapid seed germination and seedling growth, such as using pre-sprouted seed and avoiding planting in cool weather, will help to speed rice through the vulnerable stage and reduce the chances for serious damage.
Dr. Natalie Hummel and Dr. Mike Stout are entomologists with the LSU AgCenter.