Evaluation of Two Species of Nematodes for Rice Water Weevil Control, 1989
Authors: Way M. O. , Wallace R. G. , Smith K. 
Published: March 2022

The experiment was conducted at the Texas A&M University Agricultural Research and Extension Center at Beaumont and its satellite station at Eagle Lake which is about 80 mi west of Houston, TX. These sites were chosen because each has a different soil type—Beaumont; Beaumont clay: Eagle Lake; Nada fine sandy loam. Generally, in TX, rice is grown on heavy soils east of Houston and lighter soils west of Houston. Thus, if edaphic factors are important to the success of the nematodes, utilization of both sites will expand the applicability of the results. At Beaumont, 2 experiments, each analyzed separately, were conducted in adjacent basins separated by a levee. In 1 basin nematodes were applied to moist soil; in the other basin, they were applied to flood water. Each basin had 4 treatments and 4 replications arranged in a randomized complete block. Basins were disced and rototilled, and on 5 Apr fertilized with urea at 68 lb N/acre. Plots (6 × 13 ft) were staked and broadcast sown at 100 lb seed/acre on the same date. On 7 Apr basins were flooded and drained 8 Apr. Thiobencarb was applied at 4 lb (AI)/acre on 11 Apr before rice emergence which occurred 20 Apr. Basins were flooded 21 Apr and drained 22 Apr. Propanil and bentazon were applied at 3 lb (AI)/acre and 0.5 lb (AI)/acre, respectively, on 2 and 10 May. Plots were fertilized with urea at 51 lb nitrogen/acre on 15 May and a metal barrier was placed around each plot to prevent contamination by nematodes among treatments. Plots were flooded 16 May when rice was actively tillering. On 30 May Furadan 3 G at 0.6 lb (AI)/acre was applied by a hand-held shaker to designated plots in each basin. These applications were made to flood water at the recommended time in relation to the onset of the permanent flood. One basin was drained 1 Jun (16 days after the onset of the permanent flood). On 2 and 3 Jun nematode #70 (Heterorhabditii sp.) and nematode #25 (Steinemema carpocapsae) were applied, respectively, to designated plots in each basin at 500 nematodes #70/inch2 and 427 nematodes #257inch2. Rainfall prevented application of both nematodes on 2 Jun. Nematode treatments were applied in a finished spray volume of 66 gal/acre. Applications were made with a 4-nozzle boom hand-held srayer (R&D Sprayers, Inc. Model AS) equipped with 800067 tips and 100 mesh screens. Spray was propelled using CO2 at 22 psi. The boom was kept below the top of the metal barrier and conditions were calm at application time which was dusk. Thus, drift and exposure to UV radiation were minimal at time of application. The drained basin was permanently reflooded 6 Jun (3 and 4 days after application). During the drain period, soil did not dry due to rainfall and high water retention properties of the soil. On 12 Jun urea at 51 lb N/acre was applied to all plots in both basins. From 22 Jun to 26 Jun 5 soil cores (4 inch diam × 4 inch deep), each containing about 1 plant/ core, were removed from each plot. Plants were washed in a 40-mesh screen bucket, and RWW larvae and pupae were recovered and counted. Basically, the same materials and methods used at Beaumont were employed at Eagle Lake with the following exceptions. Five treatments with 4 replications were in the basin that was drained before nematode application. The additional treatment was nematode #25 applied at 250/inch2. Seed was drilled at 100 lb/acre on 24 Mar. Rows were 6 inches apart. The basins were fertilized with 188 lb of 16-20-0/acre and 33 lb of urea/acre (total of 63 lb N/acre) on 24 Mar. Rice emerged between 30 Mar and 3 Apr. Thiobencarb, propanil, and molinate were applied at 2, 3 and 3 lb (AI)/acre, resectively, on 18 Apr. The basins were flush irrigated on 4 and 21 Apr. Urea was again applied at 70 lb N/acre and 45 lb N/acre on 8 May and 1 Jun, respectively. On 9 May, each basin was flooded (this became the permanent flood in the basin to which nematodes were applied to flood water). On 19 May (10 days after the onset of the permanent flood) Furadan 3 G at 0.6 lb (AI)/acre was applied by a hand-held shaker to designated plots in both basins. On 24 May (15 days after the last flood) one basin was drained. Nematode treatments were applied die evening of 25 May. Wind was gusting so the spray boom was drawn through the rice canopy below the top of the metal barriers to minimize drift. The basin was reflooded 26 May before the soil dried. On 16 Jun, 5 soil cores were removed from each plot in the basin in which nematodes were applied to flood water. On 20 Jun the same sampling scheme was applied to the plots in the basin which was drained before application of nematodes. Data from both sites were transformed using Vx + 0.5 and subjected to ANOVA followed by DMRT where appropriate.