EVALUATION OF INSECTICIDES AGAINST DBM, 1995:

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

 

D. Dunbar

Merck Research Laboratories

7555 N. Del Mar Ave.

Fresno, CA 93711

 

R. S. Shimabuku

Cooperative Extension Service

310 Kaahumanu Ave., Bldg 214

Kahului, HI 96732

HEAD CABBAGE: Brassica oleracea L. ‘Tastie’

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

The insecticides were evaluated at the Kula Research Station, Maui Agricultural Park, from July to September. 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. Treatment plots in each block were separated by a 4.5 ft. row spacing. Blocks were separated by a 10 ft. wide space that allowed sprayer access. Total field size was 150 ft. by 109 ft. 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 nozzles 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. The first two treatments were applied using twin jet TJ 60-8006 nozzles at 25 psi with an output of 100 GPA. Thereafter, the pressures was increased to 45 psi to give an output of 125 GPA. The first treatment was made on July 18, 5 days after transplanting. Subsequent applications were made on the following dates: July 25, Aug 1, 8, 15, 22, and 29.

A pre-treatment census for larvae was made the day before the first field spray application. Subsequent evaluations were conducted on a bi-weekly schedule. Ten plants were randomly selected from each treatment plot and carefully examined for larvae. DBM immatures were counted in separate age groups: early larvae, late larvae, and pupae. Early larvae instars were larvae in the first two instars. These larvae were identified by the black colored head capsules. The late larvae were those in the last two larval instars. They were differentiated using body size and the green or brown head capsules. Pupae were easily identified by their net like cocoons.

Differences between the mean number of DBM larvae were noticed after the second survey. Both formulations of MK-244 provided the best overall control. Plants were relatively free of larval feeding damage and most of the heads were marketable at harvest. Although cabbage was harvested from the Mattch treated plots, many of the plants were extensively damaged. However, Mattch did provide better control than Thiodan 2 CO and Lannate LV which suffered greater amounts of feeding injury.

^{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). 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). DBM data was transformed by square root (X+0.5) and percent marketability by arcsin transformation prior to analysis. Untransformed means are presented.}

PART II (con.) R. F. L. Mau

(808) 956-7063