R. F. L. Mau and L. R. Gusukuma-Minuto
University of Hawaii
Dept. of Entomology
3050 Maile Way, Rm. 310
Honolulu, HI 96822
ph: (808) 956-7063
R. Oyama
Pioneer Hi-Bred International
7431 Kaumualii Hwy.
Kekaha, HI 96752


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; Tukey’s 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; Tukey’s studentized test).




Trade Composition\Common name     Formulation         name     Source
Ammo     EC         cypermethrin     FMC Corp.
Capture     EC         bifenthrin     FMC Corp.
Dimethoate     EC         dimethoate     American Cyanamid