FIELD EVALUATION OF BIO-RATIONAL INSECTICIDES FOR CONTROLLING DBM, 1993:

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) 956-6737

FAX: (808) 956-2428

 

W. S. Ruggero

AgriDyne Technologies, Inc.

2401 So. Foothill Drive

Salt Lake City, UT 84109

 

M. H. Kijima

Maui County Farm Bureau

P. O. Box 148

Kula, HI 96790

HEAD CABBAGE: Brassica oleracea L. 'Tastie'

Diamondback moth (DBM); Plutella xylostella (Linnaeus)

DBM parasite (DBMP); Cotesia plutella (Kurdijumov)

Aphid parasite (APA); Lysiphlebus testaceipes (Cresson)

Aphid predator (APR); Allograpta obliqua (Say)

Green lacewing (GLW); Chrysopa sp.

Insecticides were evaluated at the substation of the Kula Research Station, Maui Agricultural Park from August through October. The field was set up in a randomized block design with five treatments and four replications (blocks). Each treatment plot measured 70 ft. by 7.5 ft. It consisted of six rows of cabbage in 3 beds on 36 inch centers and 18 inch in-row spacing. Adjacent rows were offset to allow equidistant plant spacing between rows. Treatment plots in each block were separated by a 3 ft. border. Blocks were separated by a 10 ft. border that allowed sprayer access. Total field size was 150 ft. by 109 ft.

Treatments were applied using a diaphragm pump, hydraulic jet agitator and a 30 ft. boom attached to a half ton pick-up truck. The boom was set with three banks of solid cone (TG-3, Spraying Systems) nozzles that coincided with row spacing. Each group of nozzles had its own line from the main tank; therefore, spray output to specific treatment plot was easily controlled. Sprays were applied at 40 psi at a rate of 150 gallons per acre on a weekly basis from one week after transplanting to one week before harvest.

Post treatment surveys were conducted on a weekly basis six days after treatment. Ten plants were randomly selected from the two center rows and removed for examination of insects. DBM immatures were counted in separate age groups: early larvae, late larvae, and pupae. Early larvae were those in the first two larval instars. They were identified by their small size and the occurrence of black colored head capsules. Late larvae were those in the last two larval instars. They were identified by their larger size and the occurrence of green or brown head capsules. Pupae were easily identified by their net like cocoons.

After the first spray, all treatments decreased the number of late larvae when compared to the untreated check. DBM populations increased substantially over the duration of the trial and many larvae were observed in all plots. Differences in the severity of insect feeding damage were visually noticeable after three applications. The plants in the untreated check and Align at 11 oz/A plots were damaged by insect feeding on almost all leaves. Although the other treatments plots also exhibited extensive feeding damage, there were plants that had minimal injury to the wrapper leaves. The lowest number of early instar larvae were found in the Xentari treatment plots throughout the trial. Late larvae was best controlled by Xentari and the higher Align rates (16 oz/A and 21 oz/A). Evaluation of harvested heads showed that there was a greater proportion of marketable heads in the Xentari and Align at 21 oz/A treated plots compared to Align at 11 oz/A and the untreated check treated plots. Marketability could probably be improved with shorter spray intervals.

DBMP, APA, APR, and GLW occurred throughout all of the plots. There were no apparent differences in the distribution of the beneficial insects when untreated and treated plots were compared.

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) 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) (insect count) and arcsine (percent marketability) prior to analysis. Untransformed means are presented.