EFFICACY OF FUMIGANTS FOR CONTROLLING THE ROOT APHID, 1994.

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

University of Hawaii

Department of Entomology

3050 Maile Way, Room 310

Honolulu, HI 96822

Phone: (808) 956-6737

FAX: (808) 956-2428

 

R. S. Shimabuku

Cooperative Extension Service

310 Kaahumanu Ave., Bldg 214

Kahului, HI 96732

HEAD CABBAGE: Brassica oleracea L. "Tastie"

Root Aphid; Pemphigus sp.

Fumigants were tested to control a new root aphid found in the farming area of Kula located on the Hawaiian Island of Maui. The field trial was installed on a cooperating grower's farm at Kula, Maui in a field that contained broccoli heavily infested by the pest. The experimental plots were adjacent to a broccoli planting that was also heavily infested by the root aphid. The adjacent broccoli crop was removed by the grower 5 weeks after the field trial began.

The four treatments tested were Telone II (30 gal/A), Vapam (60 gal/A), Di-Syston 15G (13.4 lbs/A) as a treated check, and an untreated check. The field site was plowed on 24 Nov 1994 and fumigants were applied 2 weeks later using a tractor mounted injector. Head cabbage seedlings in the 6-8 true leaf stage were planted 2 weeks after fumigants were applied. The Di-Syston treatment was applied in-furrow immediately prior to transplanting.

A randomized block plot design with three replications was used. Each treatment replication consisted of four rows of cabbage with 25 plants per row at 18 inches inter plant spacing. Treatment plots were separated by a 3 feet buffer. The treatments were evaluated at 3, 7, and 12 weeks after planting to assess aphid populations on the roots. During each evaluation, the roots of 15 plants were taken from each treatment plot and individually bagged. Each root sample was washed in a calcium chloride solution (1 tablespoon/gallon water). The aphids floated to the surface and were counted.

The treated check, Di-Syston 15 G, provided excellent aphid control throughout the test. In comparison with the treated and untreated check treatments, both of the fumigant treatments provided poor control throughout the growing season. Although statistical differences were found when comparing the fumigant and untreated check treatments, the actual differences during the 3 and 7 week evaluation dates were minimal. However, at the end of the experiment (12 weeks), aphid numbers on plant roots in the Telone II treatment were approximately one-half that of the Vapam treatment and one-third that of the untreated check. In comparing aphid distribution on plants, we found that approximately 90% of the plants sampled from the Telone II, Vapam, and untreated check plots were infested with the root aphid where only 30% of the plants in the Di-Syston plots were infested. Many alate-form aphids were found in the Telone II, Vapam, and untreated check treatments on the final evaluation date. None were found on Di-Syston treated plants.

Means in each column followed a different letter are significantly different (Tukey's studentized range

test P<0.02, SAS Institute, version 6.04). Data was transformed by square root (x+0.5) prior to analysis.

Untransformed means are presented.