EVALUATION OF EMAMECTIN BENZOATE (MK-244) AND OTHER 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 May to June. 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 treatment was applied using hollow cone TX-18 (Spraying Systems) nozzles at 100 psi. Due to excessive drift caused by the small droplet size, the nozzles were changed to TX-26 for the second to fifth treatment application. The pressure was reduced to 45 psi to give an output of 100 gallons per acre. For the last two treatments, the twin jet TJ-60 8006 nozzles at 25 psi were used for an output of 100 gallons per acre. The first treatment was made on 16 May, 12 days after transplanting. Subsequent applications were made on the following dates: May 23 and 30, June 6, 13, 20, and 27.

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.

Significantly fewer late larvae were found in the MK-244 and B. t. treated plots at survey 2. However, only MK-244 controlled larval populations to harvest. Plants treated with MK-244 were relatively free of fresh feeding injury whereas the Pounce and untreated check plants were extensively damaged. Plants treated with B. t. products exhibited moderated levels of damage. At harvest, more marketable heads were harvested from the MK-244 treated plants compared to the other treatments.

^{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) and percent marketable by arcsin ransformation prior to analysis. Untransformed means are presented.}