EVALUATION OF BACILLUS THURINGIENSIS INSECTICIDES AGAINST DBM, 1994:

R. F. L. Mau and L. R. Gusukuma-Minuto

University of Hawaii

Dept. of Entomology

3050 Maile Way, Rm. 310

Honolulu, HI 96822

Phone: (808) 956-7063

 

K. Dart

Mycogen Corp.

1612 Horse Lake Rd.

Wenatchee, WA 98801

 

R. S. Shimabuku

Cooperative Extension Service

310 Kaahumanu Ave., Bldg. 214

Kahului, HI 96732

HEAD CABBAGE: Brassica oleracea L. 'Supreme Vantage'

Diamondback moth (DBM); Plutella xylostella (L.)

The insecticide was evaluated at the Kula Research Station, Maui Agricultural Park, from October to December. The field was set up in a randomized block design with six treatments and four replications (blocks). Each treatment plot measured 70 ft. by 7.5 ft. It consisted of four rows of cabbage on 36 in. centers and 18 in. in-row spacing. Adjacent rows were offset to allow equidistant plant spacing between rows.

Treatments were applied using a tractor mounted with a PTO driven spray pump equipped with a 30 ft. boom. The boom was set with three banks of hollow cone nozzles (TX-26, Spraying Systems) that coincided with row spacing. Each group of nozzles had its own line from the main tank, therefore, spray output to specific treatment plots could be easily controlled by the sprayer operator. Sprays were applied at 100 psi at a rate of 150 GPA. Applications were made at 3- to 4-day intervals according to DBM larval and egg densities observed during the prior bi-weekly insect survey. Applications were made on Oct 6, 10, 13, 17, 20, 27, 31; Nov 3, 7, 10, 14, 17, 24; Dec 1, and 5 for a total of 15 applications. Post treatment evaluations were conducted on a bi-weekly basis. Ten plants were randomly selected from each treatment plot and carefully examined for immatures.

Significant differences in the number of larvae were observed between the untreated check and all treatments beginning from the second post treatment survey date. This trend continued throughout the trial. DBM larval densities were rather low during the field evaluation. Nonetheless, there were visible differences in the amount of feeding injury in the different treatment plots. Mattch treated plots exhibited significantly less insect feeding damage and resulted in a higher percentage of marketable cabbage. The higher rate of Mattch provided superior protection against DBM feeding damage. MVP provided moderate levels of marketable yield. Poor marketable yields were obtained in the Agree and Xentari treated plots.

^{Means in each column followed by a different letter are significantly different (Tukey's studentized range test P<0.001). Data was transformed by square root (X+0.5) prior to analysis. Untransformed means are presented.}

^{Means in each column followed by a different letter are significantly different (Tukey's studentized range test P<0.001 SAS Institute, version 6.04). Data was transformed by square root (X+0.5) (inzect counts) and arcsine (percent marketable) prior to analysis. Untransformed means are presented.}