INSECTICIDE EFFICACY 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

 

R. S. Shimabuku

Cooperative Extension Service

310 Kaahumanu Ave., Bldg 214

Kahului, HI 96732

 

K. W. Dunster

Rhone-Poulenc Ag Co.

P. O. Box 598

Byron, CA 94514

HEAD CABBAGE: Brassica oleracea L. ‘Tastie’

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

Three 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 five treatments and four replications (blocks). Each treatment plot consisted of a single row of cabbage planted at 18 inch between plant spacing. Treatment plots in each block were separated by a 24 inch row spacing. Blocks were separated by a 36 inch spacing. Total field size was 68 ft. by 70 ft. Treatments were applied using a CO₂ backpack sprayer set at 60 psi with an output of 100 GPA. One hollow cone nozzle (TX-26) was used per row. The first treatment was applied one week after transplanting into the field on 18 July. Subsequently, six applications were made weekly until the week before harvest on the following dates: 25 Jul, 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 for a total of five surveys. Ten plants were randomly selected from each treatment plot and carefully examined for larvae. For survey 1 and 2, plants were assessed for larvae in the field. Plants were removed for survey 3 and at harvest (survey 5). Plants were not assessed for larvae in survey 4 to prevent damage to the heading plants. 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. Larval damage ratings (0-5) were assigned to each treatment plot in the third and fourth survey and to each mature head at harvest. In assigning a damage rating, the developing part of the plant or marketable part of the head were examined for insect damage. A ‘0’ rating was assigned if there were no damage. The numerical rating increased as the degree of insect damage increased.

Differences in DBM larvae numbers among the treatments were evident from the second survey. Throughout the study, there were lower numbers of larvae on the cabbage treated with EXP 60720A. As a result the cabbage in these plots had comparatively lower damage ranks when compared to plants in the other treatments. EXP 60720A controlled caterpillars from the onset and plants were relatively damage free throughout the study. The higher rate of EXP 60720A proved to be more effective as indicated by the higher rate of marketable cabbage. Neemix + Xentari treated plots had significantly lower damage ranks than the untreated check; however, many of the plants were extensively damaged. Although the Neemix + Xentari tank mix provided better control than Xentari alone, the marketable yields were very low.

^{Means in each column followed by a different letter are significantly different (Tukey's studentized range test P<0.01). 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<0.01). 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<0.01). Data was transformed by square root (X+0.5) prior to analysis. Untransformed means are presented.}