ONION THRIPS MANAGEMENT ON BULB ONION, 1998:

R. F. L. Mau and L. R. Gusukuma-Minuto

University of Hawaii CTAHR

Dept. of Entomology

3050 Maile Way, Rm. 310

Honolulu, HI 96822

Phone: (808) 956-7063

FAX: (808) 956-5888

e-mail: maur@avax.ctahr.hawaii.edu

ONION: Allium cepa L. ‘Grano 1015Y’

Onion thrips (OT);

Thrips tabaci Lindeman

The insecticides were evaluated at the Kula Research Station, Kula, Maui, Hawaii. Treatments were placed in a RCB design with nine treatments and four replications. Plants were transplanted into plots measuring 30 ft. long by two beds wide. The beds were on 2-ft. centers. Onion seedlings were planted into the beds on 14 May. The beds were arranged in two rows with 8 inches between plants and a total of 45 plants per row. The plots were irrigated using trickle irrigation. Insecticide treatments were made at 60 psi and at a rate of 100 gallons per acre using a compressed carbon dioxide hand sprayer equipped with twin-jet nozzles (TJ-6502, Spraying Systems). The organosilicone adjuvant, Silwett L-77 (8 oz./A, Loveland Co.) was added to the spray mixes to facilitate wetting of the onion foliage. Treatments were initiated on 30 Jun after OT numbers exceeded 10 OT/plant. Thereafter, treatments were made only if the treatment threshold was exceeded. The minimum treatment interval was 7 days.

Weekly in-field surveys were conducted by counting all OT on ten randomly selected plants in each treatment plots. Bi-weekly plant removal surveys were also conducted using the following procedures. Ten plants were randomly selected and the roots and most of the leaves were removed. The remaining portions of the plant (stem, leaf axils, and 2 in. of leaves) were each bagged separately. In the laboratory, each sample was washed in a detergent solution. OT were collected in a 150-mesh sieve, transferred into plastic 20 ml vials, preserved with 70% ethyl alcohol, and counted at a later date.

All insecticide treatments reduced OT population densities when compared with the untreated check. Success was more effective at the 6, 8, and 10 oz./A rates than at the 4 oz. rate. Treatment with Success at the higher rates provided comparable control as Warrior CS stand-alone treatments, but there were differences in the number of applications required using the 10 thrips per plant threshold. Three applications were required for single and rotation treatments of Warrior + Agri-Dex spray oil compared with 4-5 for treatments with the Silwett adjuvant. The results also showed that rotation of Success and Warrior might be useful in integrated resistance management program.

Means in the same column followed by a different letter are significantly different (P<0.01, SAS for Windows version 6.12). Data was transformed by square root (Y+0.5) prior to analysis. Untransformed means are presented.

¹Rotation #1 = Warrior CS @ 0.02 lb. ai/A; Success @ 6.0 oz./A to be sprayed in alternating order based on OT threshold.

²Rotation #2 = Warrior CS @ 0.02 lb. ai/A; Success @ 8.0 oz./A to be sprayed in alternating order based on OT threshold.