EVALUATION OF ALERT 2 SC AGAINST THE CORN THRIPS, 1996:

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 T11’

Corn thrips (CT); Frankliniella williamsi Hood

The corn thrips is an important pest of the corn seed industry in Hawaii. Its pest status has steadily increased due to the growing importance of the corn seed industry. If the insect is not controlled, the pest causes direct feeding injury that results in plant stunting or death of young corn plants. At these injury levels, economic reductions in seed yield of 70 to 100 percent have occurred.

The field evaluation was conducted at Pioneer Hi- Bred International’s field located near Kekaha on the Hawaiian island of Kauai. Two rates of Alert, a treated check (Capture 2 EC @ 0.1 lb. ai/acre) and an untreated check was set in a randomized block design with four replications. Each treatment replication consisted of ten rows of corn at 30 ft. length. The corn seeds were planted on 18 Mar on 30 in. centers and 8.5 in. in-row plant spacing. Treatments were separated by a 5 ft. non-spray buffer area. Adjacent replications were separated by a 10 ft. non-spray buffer area. Total area used for the test was approximately 0.22 acre. A John Deer 6500 sprayer was used for treatment applications. Sprays were applied at 33 psi with an output of 40 GPA. The boom was equipped with two twin jet 8004 nozzles per row, one directly over and one between each row. Treatment applications were initiated four weeks after planting the field when the plants were in the 4-5 leaf stage. Treatments were made on 11 and 18 Apr.

Whole plant samples were taken four times during each field trial. On each evaluation date, 10 plants from each treatment replication were randomly selected using a zigzag pattern. Each plant was cut near the base and placed in separate plastic bags. Pre-treatment samples were taken 1-day before the first chemical application. Post-treatment evaluations were made 5-days and 7-days after the first spray application. Subsequently, the fourth evaluation was made 5-days after the second spray application.

Plant samples were processed in the laboratory was washing in a detergent solution. All of the leaves were removed ensure that all thrips were released from the leaf whorls. The thrips were collected on a 150 mesh sieve and were preserved in 70% alcohol. Separate tallies were kept for the first instar larvae (LI), second instar larvae (LII), and adults (A).

Significant reductions in LII numbers occurred within 5 DAT 1. Reductions of LII occurred more rapidly at the higher rate of Alert but both rates were efficacious. The treated check also successfully reduced the number of LII. 7 DAT 1, Alert and Capture provided significant reductions in LI and LII. Similar trends were observed in samples collected 5 DAT 2. No differences in the adult numbers were observed until the last survey. This may have resulted from the effectiveness of treatments on the larvae resulting in reduced adult development numbers rather than on the effectiveness on adults.

^{Means in the same column within each survey date are significantly different (Tukey’s studentized range test P< .01; SAS for Windows version 6.08). Data transformed by square root(Y+0.5) prior to analysis. Untransformed means are presented.}

^{Means in the same column within each survey date are significantly different (Tukey’s studentized range test P< .01; SAS for Windows version 6.08). Data transformed by square root(Y+0.5) prior to analysis. Untransformed means are presented.}

^{Means in the same column within each survey date are significantly different (Tukey’s studentized range test P< .01; SAS for Windows version 6.08). Data transformed by square root(Y+0.5) prior to analysis. Untransformed means are presented.}

^{Means in the same column within each survey date are significantly different (Tukey’s studentized range test P< .01; SAS for Windows version 6.08). Data transformed by square root(Y+0.5) prior to analysis. Untransformed means are presented.}