Water-Seeded Rice

Dr. Ronnie Levy, Extension Rice Specialist at LSU wrote this article for the April 2022 issue of Rice Farming Magazine. I clipped it out and thought, “this will come in handy someday!” I am putting this out there again because our organic rice producers are facing some real problems with weeds in rice including weedy rice, hemp sesbania, jointvetch and certainly weedy grasses.

Last year I was at Joe Broussard’s farm near Nome, looking at a rice field that was headed out and looking great. On the other side of the levy was a field choked with weeds – what was the difference? One was water-seeded rice, and the other was not. Joe had used water seeding and his flood to control weeds “the old-fashioned way!” So, read this article by Dr. Levy and think about it……

Rice Farming, April 2022. Dr. Ron Levy. “Most rice is drill-seeded in Louisiana — about 80% — but there is a renewed interest in water-seeding rice for weedy rice suppression (or many other weeds in organic systems).

The most common water-seeding method in Louisiana is the pinpoint flood system. After seeding, the field is drained briefly. The initial drain period is only long enough to allow the radicle to penetrate the soil (peg down) and anchor the seedling. A three- to five-day drain period is sufficient under normal conditions.

The field then is permanently flooded until rice nears maturity (an exception is midseason drainage to alleviate straighthead (physiological problem of rice) under certain conditions).

In this system, rice seedlings emerge through the floodwater. Seedlings must be above the water surface by at least the 3 to 4-leaf rice stage. Before this stage, seedlings normally have sufficient stored food and available oxygen to survive. Atmospheric oxygen and other gases are then necessary for the plant to grow and develop.

The pinpoint flood system is an excellent means of suppressing weedy rice emerging from seeds in the soil because oxygen necessary for weedy rice germination is not available as long as the field is maintained in a flooded (or saturated) condition. A continuous flood system, another water-seed system, is limited in Louisiana. Although similar to the pinpoint flood system, the field is never drained after seeding.

Regarding the water-seeded systems, a continuous flood system is normally best for red rice suppression, but rice stand establishment is most difficult. Even the most vigorous variety may have problems becoming established under this system. Inadequate stand establishment is a common problem in both systems.

Fertilization timing is the same for both the pinpoint and continuous flood systems. Phosphorus (P), potassium (K), sulfur (S) and zinc (Zn) fertilizers are applied preplant incorporated as in the dry-seeded system. Once the field is flooded, the soil should not be allowed to dry.

If the nitrogen requirement of a particular field is known, all nitrogen fertilizer can be incorporated prior to flooding and seeding or applied during the brief drain period in a pinpoint flood system. Additional N fertilizer can be applied at the beginning of reproductive growth between panicle initiation and panicle differentiation (2-millimeter panicle).

Water-seeding has been used in the past for weed control. Will water-seeding make a comeback to help with weedy rice suppression (or possibly for organic rice producers)?”

Another issue water-seeded rice may experience.

Rice Seed Midges – The larvae of these insects (Order Diptera, Family Chironomidae, Genera Tanytarsus and Chironomus) are aquatic and can be very abundant in rice fields. The adults are small, gnat-like flies that typically form inverted pyramidal mating swarms in the spring over stagnant or slow-moving water. Female flies lay eggs in ribbons on the water surface. The larvae hatch and move downward to the flooded substrate where they build protective “tubes” of silk, detritus, and mud. These brown, wavy “tubes” are easily observed on the mud surface of rice paddies. Occasionally, the larvae will exit the tubes and swim to the surface in a whiplike fashion, similar to that of mosquito larvae. Midge larvae can damage water-seeded (pinpoint or continuous flood) rice by feeding on the sprouts of submerged germinating rice seeds. Damage can retard seedling growth or kill seedlings; however, the window of vulnerability to midge attack is rather narrow (from seeding to when seedlings are about 3 inches long).

Control rice seed midge problems by dry seeding, then employing a delayed flood, or by draining water-seeded paddies soon after planting. Thus, a pinpoint flood should reduce the potential for rice seed midge damage relative to a continuous flood. For water-seeded rice, reduce rice seed midge problems by increasing the seeding rate and planting sprouted seed immediately after flooding.

Management of Rice Seed Midge – Insecticide Trial Results

Click on the above link to read a great article from California rice researchers about an experiment they did on Rice Seed Midge control and some of the most effective treatments are organic and soon to be OMRI approved.