Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Charles D. Pless

Committee Members

Ernest Bernard, Arthut J. Stewart, Dennis Deyton

Abstract

Petroleum dormant spray oils have been used to manage San Jose scale (SJS), Quadraspidiotus perniciosus (Comstock), on apple trees since the introduction of SJS into the United States in the 1870's. Although studies have shown that cottonseed or soybean oil could be used to control several aphid, whitefiy, and mite species on vegetables and cotton, few studies have examined the use of soybean oil as dormant sprays on fruit trees.

The objectives of this study were to determine: 1) the efficacy of soybean oil dormant sprays for management of SJS on apple, and 2) life cycles of SJS and its predominant parasitoid, Aphytis sp. (Hymenoptera: Aphelinidae), in Tennessee. In 1993, an Aphytis sp. was determined in a preliminary survey to be the most abundant SJS parasitoid.

Dormant oils were applied to 'Bounty' apple trees in a commercial orchard on 14 Feb 1994, and 20 Feb 1995. The treatment units were single trees with five replications (completely randomized design). The following treatments were applied to run-off with a hand-gun at 60 psi: 1) 6% (v/v) degummed soybean oil with 0.6% (v/v) Latron B-1956 sticker spreader (Rohm & Haas, Philadelphia, Pennsylvania) as an emulsifier, 2) 3.0% degummed soybean oil with 0.6% Latron B- 1956 sticker spreader as an emulsifier, 3) 3% 6E Volck Supreme Oil (VC1023 Valent Corporation) prepackaged with an emulsifier (X-77), and 4) an untreated control.

SJS crawlers on bark were counted for three min per tree weekly during the growing season with a 16x hand lens. Adult Aphytis were also counted for three min per tree weekly with a l<6x hand lens. Three pheromone traps were used to monitor male scale emergence in the orchard weekly (8 Mar-10 Nov 1994, and 1 Mar-1 Jun 1995). Separation of means was determined by Tukey's HSD (P=0.05) on first, second, and third generation crawler data in 1994 and first generation crawler data in 1995. Twenty apple fruit from each tree were evaluated for first generation SJS infestation on 13 Jun 1995.

The male SJS flight periods occurred during 15 Apr-17 May, 14 Jun-29 Jul, and 1 Aug-26 Sept 1994. Crawler SJS emergence periods occurred during 17 May-28 Jun, 7 Jul-30 Aug, and 7 Sept-24 Oct 1994. Numbers of adult Aphytis peaked between 24 Aug and 26 Sept 1994.

Both 3% petroleum oil and 6% soybean oil sprays reduced first and second SJS crawler generations by > 93% in 1994; first generation was reduced by 98% in 1995. The 3% soybean oil reduced first and second generations by 60% in 1994 and 83% in 1995. In 1995, apple fruit infestation by first generation SJS on the 3% soybean, 6% soybean, and 3% petroleum oil treated-trees did not differ. Averages (± SD) of first generation SJS per fruit (n = 100) on treated trees were: 3% soybean oil, 3.1 ± 3.7; 6% soybean oil, 1.2 ± 0.8; 3% petroleum oil, 0.9 ± 0.9; and untreated controls, 139.3 ± 80.2.

This study demonstrated that degummed crude soybean oil dormant sprays were effective for management of SJS on apple trees. Data from this study suggest that SJS had three generations in 1994. The abundance of Aphytis, compared to other parasitoids, suggests that this wasp was the major parasitoid of SJS in this study.

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