EVALUATION OF AN IGR INSECTICIDE, RH-2485, FOR CONTROL OF DBM AND OTHER CATERPILLARS ON HEAD CABBAGE, 1996:

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

HEAD CABBAGE: Brassica oleracea L. ‘Tastie’

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

Cabbage looper (CL); Trichoplusia ni (Hubner)

Imported cabbageworm (ICW); Pieris rapae (L.)

Imported cabbage webworm (ICWW); Hellula undalis (Fabricius)

The insecticides were evaluated at the Kula Research Station, Maui Agricultural Park, from April to June. 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 in. between plant spacing. 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 five days after transplanting into the field on 23 Apr. Subsequently, six weekly applications were made until the week before harvest on the following dates: 30 Apr, 7, 14, 21, 28 May, 4 Jun. The treated check treatment consisted of Bacillus thuringiensis aizawai (BTA) or Proclaim applied using the University of Hawaii DBM resistance management protocol. BTA products are used prior to the cupping stage of growth. Proclaim 0.15 EC @ 6.0 oz./A is applied if DBM densities exceed 1.0 larva per plant. Proclaim is used after cupping if DBM densities exceed 0.5 larva/plant and 1-2 applications are made during the two weeks prior to harvest if DBM is present. Larval thresholds were determined by making larval counts on 10 plants/treatment replication. Mattch @ 2.0 qt./A was the BTA product used and it was applied on 23, 30 Apr, 7, 14 May. Proclaim was applied on 21 and 28 May.

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 the pretreatment and 6 May surveys, plants were assessed for larvae in the field. Plants were removed for the 20 May survey and at harvest.

RH-2485 was not effective in controlling DBM despite its low population density. The few larvae on the RH-2485 treated plants penetrated the cabbage heads and produced damage below the wrapper leaves rendering the harvested heads un-marketable. RH-2485 was effective in controlling ICW, which was the dominant lepidopteran species observed throughout most of the experiment. ICWW and CL larvae occurred at trace levels, however, it appeared that RH-2485 was effective in controlling these pests.

^{Means in each column followed by a different letter are significantly different (Tukey's studentized range test P<0.001 SAS for Windows, version 6.11). 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 for Windows, version 6.11). Data was transformed by square root (X+0.5) prior to analysis. Percent marketable datum was transformed by arcsin prior to analysis. Untransformed means are presented.}