EVALUATION OF INSECTICIDES AGAINST THE CORN THRIPS, 1995:
CORN: Zea mays L. Pioneer PO2
Corn thrips; Frankliniella williamsi Hood
The insecticides Ammo 2.5 EC and Capture 2 EC were tested in two field trials from February to April. Trials were conducted at the Pioneer Hi-Bred International, Inc. fields located near Kalaheo on the Hawaiian Island of Kauai. For each trial, the same treatments and field design were utilized. Seven treatments were set in a randomized block design with four replications. Each treatment replication consisted of six rows of corn at 60 ft. length. The corn seeds were planted on 30 in. centers and 8.5 in. in-row spacing. Treatments were separated by a 5 ft. non-spray buffer area. Adjacent replications were separated by a 10 ft. non-spray buffer area. Extra corn rows were planted in the field area therefore all of the area was not utilized. The total area of the field actually used for the experiment was 0.83 A. The field for trial 1 was planted on 17 Jan and for trial two on 16 Mar. The fields were irrigated by drip irrigation at 3-4 day intervals.
Two spray applications were made at 1-week intervals with a Hagie 8250 sprayer. Sprays were applied at 40 psi with a tractor speed of approximately 3 mph. The boom ran on three sets of nozzles with 16-17-16 nozzles per set, respectfully. The nozzles distance on the boom corresponded with row spacing therefore sprays were applied with one nozzle per row. When treatments were made, only the six nozzles that corresponded to the six rows of test corn were opened. In trial 1, 8004 hollow cone nozzles and in trial 2, twin jet 6504 nozzles were used. In both field trials, Ammo and Capture were applied at a rate of 50 GPA. Dimethoate was used at 100 GPA for trial 1 and 50 GPA in trial 2. The adjuvant Silwett L-77 was used at 8.0 oz./A for treatments applied at 50 GPA and at 4.0 oz./A at 100 GPA. Treatments were made on 24 Feb and 2 Mar for trial 1 and on 8 Apr and 13 Apr for trial 2.
Whole plant samples were taken four times during each field trial. Pre-treatment samples were taken 1-2 days before the first chemical application. Post-treatment evaluations were made 2-3 days and 4-6 days after the first spray application. Subsequently, the fourth evaluation was made 3-4 days after the second spray application. On each evaluation date, 10 plants from each treatment replication were randomly selected using a zigzag pattern. The plants were severed at the base and placed in separated plastic bags. A total of 280 plant samples were taken at each evaluation date. Plant samples were processed in the laboratory. Approximately 2 ml of liquid detergent was added to each plastic bag containing the plant sample. The bag was filled with water and then shaken for 1 minute. The contents were poured into a plastic bucket filled with approximately 1.5 liters of tap water. The empty plastic bag was rinsed with the water to remove thrips caught on the inside surface. The entire corn plant was placed in the detergent solution and disassembled to ensure that all thrips were released from the leaf whorls. The detergent solution containing the thrips was then passed through combined 12 and 200 mesh sieves to collect the thrips. The thrips were transferred to plastic 20 ml vials and preserved with 70% ethyl alcohol. Thrips samples were evaluated using a dissecting microscope. Separate tallies were kept for the first instar larvae (LI), second instar larvae (LII), and adults (A).
In both field trials, Ammo and Capture provided better control than did Dimethoate when the pre-treatment means were compared with the means at the end of the trial, however, more effective control was observed in the first trial. This can be attributed to the greater difficulty in obtaining spray coverage in the leaf whorls. The corn plants in the second trial were approximately 2 weeks younger at the start of the trial, therefore, the smaller plants had a tighter leaf whorl. Although the data suggests insecticide impact on adult thrips, we do not believe adult kill by Ammo or Capture is significant. There is a strong possibility that adult data was influenced by adult thrips migrating into the treated plots from the untreated plants and from adult emerging form the soil.
Trial 1
Mean number of thrips/10 plants |
Pre-treatment (23 Feb) | 3 DAT 1 (27 Feb) | 6 DAT 1 (2 Mar) | 4 DAT 2 (6 Mar) |
Treatment | Rate/Acre | LI | LII | A | LI | LII | A | LI | LII | A | LI | LII | A | |||||
Ammo 2.5 EC | 2.6 oz. | 8.1 cd | 111.1ab | 20.8abc | 8.4d | 65.8bc | 16.5b | 32.1ab | 6.2c | 21.3ab | 3.4c | 6.8c | 12.0bc | |||||
Ammo 2.5 EC | 5.1 oz. | 10.0bc | 83.3b | 16.2c | 14.7d | 26.6d | 14.7b | 13.1c | 4.2c | 18.0b | 1.5c | 2.5d | 5.8d | |||||
Ammo 2.5 EC | 7.7 oz. | 15.2ab | 113.9ab | 18.2bc | 15.5bc | 75.0b | 16.7b | 29.2ab | 3.7c | 23.5ab | 1.0c | 2.0d | 10.0c | |||||
Capture 2 EC | 3.2 oz. | 3.6d | 102.7ab | 21.6abc | 10.7cd | 30.0d | 17.1b | 24.0bc | 3.2c | 21.1ab | 2.0c | 4.5cd | 12.1bc | |||||
Capture 2 EC | 6.4 oz. | 23.4a | 100.0ab | 22.4ab | 11.8cd | 44.1cd | 16.8b | 22.8bc | 4.6c | 19.7b | 2.0c | 3.2cd | 13.1bc | |||||
Dimethoate 2.67 | 1.0 pt. | 5.7cd | 81.2b | 17.9bc | 29.8a | 31.0d | 17.4b | 33.2ab | 21.6b | 24.0ab | 8.2b | 14.6b | 16.0b | |||||
Untreated check | --- | 20.0a | 138.0a | 26.3a | 30.3ab | 125.4a | 25.7a | 36.8a | 30.6a | 26.8a | 39.7a | 39.6a | 37.1a |
Means within the same colunm followed by a different letter are significanltly differrent (P<0.05; Tukeys studentized test).
Trial 2
Mean number of thrips/10 plants |
Pre-treatment (6 Apr) | _2 DAT 1 (10 Apr) | 4 DAT 1 (12 Apr) | 4 DAT 2 (17 Apr) |
Treatment | Rate/Acre | LI | LII | A | LI | LII | A | LI | LII | A | LI | LII | A | |||||
Ammo 2.5 EC | 2.6 oz. | 39.5a | 23.0a | 38.7a | 11.2bc | 15.5bc | 50.0b | 5.2a | 41.5ab | 42.1a | 4.8a | 7.8b | 10.8b | |||||
Ammo 2.5 EC | 5.1 oz. | 35.3ab | 19.6ab | 34.8a | 4.9d | 12.5c | 43.3b | 3.9a | 23.6c | 37.4a | 1.3b | 1.0c | 4.1c | |||||
Ammo 2.5 EC | 7.7 oz. | 26.6b | 16.8ab | 37.3a | 5.2cd | 8.7c | 30.6c | 3.8a | 21.2c | 35.0a | 0.7b | 1.4c | 3.8c | |||||
Capture 2 EC | 3.2 oz. | 25.6ab | 15.6ab | 34.9a | 0.2bcd | 14.7bc | 44.5bc | 4.1a | 27.9bc | 40.2a | 1.5b | 4.8b | 10.6b | |||||
Capture 2 EC | 6.4 oz. | 25.4ab | 13.7b | 31.0a | 9.2cd | 13.4bc | 39.8bc | 3.4a | 22.9c | 36.4a | 5.0a | 2.5bc | 9.4bc | |||||
Dimethoate 2.67 | 1.0 pt. | 26.3b | 13.1b | 32.4a | 18.4b | 21.1b | 53.2b | 4.0a | 29.8bc | 39.3a | 6.0a | 4.4b | 10.4b | |||||
Untreated check | --- | 23.8b | 13.5b | 33.6a | 31.8a | 39.4a | 76.4a | 4.1a | 44.3a | 42.6a | 5.9a | 8.1a | 22.5a |
Means within the same colunm followed by a different letter are significanltly differrent (P<0.05; Tukeys studentized test).
Trade Composition\Common name | Formulation | name | Source | ||||||||
Ammo | EC | cypermethrin | FMC Corp. | ||||||||
Capture | EC | bifenthrin | FMC Corp. | ||||||||
Dimethoate | EC | dimethoate | American Cyanamid | ||||||||