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  • Author or Editor: C.D. Pless x
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Emulsions of degummed soybean (Glycine max L.) oil were compared to a petroleum oil emulsion for efficacy against winter populations of San Jose scale [Quadraspidiotus perniciosus (Comstock); Homoptera: Diaspididae] and European red mite [Panonychus ulmi (Koch); Acari: Tetranychidae] on dormant apple (Malus domestica Borkh.) trees and terrapin scale [Mesolecanium nigrofasciatum (Pergande); Homoptera: Coccidae] on dormant peach [Prunus persica (L.) Batsch.] trees. In laboratory tests, more than 94% of San Jose scale was killed on stems dipped for 1 second in 5.0% or 7.5% soybean oil or 5.0% petroleum oil. Mortality of terrapin scale exceeded 93% on peach stems dipped for 1 second in 7.5% soybean oil or 5.0% petroleum oil. No European red mite eggs survived on apple stems dipped for 1 second in 2.5%, 5.0%, or 7.5% soybean oil, or 5.0% petroleum oil. In field tests, >95% of San Jose scale died on apple trees sprayed with one application of 2.5% petroleum oil or 5.0% soybean oil; two applications of these treatments or 2.5% soybean oil killed all San Jose scales. One or two applications of 2.5% petroleum oil or 5.0% soybean oil killed 85% and 98%, respectively, of the terrapin scales on peach trees. Soybean oil shows promise as a substitute for petroleum oil for winter control of three very destructive fruit tree pests.

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Twigs from peach trees heavily infested with terrapin scale (Lecanium nigrofasciatum) and from apple trees heavily infested with San Jose scale (Quadraspidiotus perniciosus) were collected in January 1993. The twigs (10 replications) received no treatment (control) or dips for 1 second in 2.5 or 5.0% petroleum (dormant) oil (PO), 2.5, 5.0, or 7.5% soybean oil (SO), 5.0% corn oil (CO), 5.0% canola oil (CAO), or 0.6% Latron AG44M emulsifier. All vegetable oil treatments contained 0.6% Latron AG44M. After 2 weeks, mortalities of San Jose scale on apple (“blackcap” stage, 10 per twig) and terrapin scale on peach (mean of 36 scale insects per twig) were visually determined. Approximately 2% of the terrapin scale and 6% of San Jose scale on control twigs were dead at time of evaluation. Twigs treated with 2.5 or 5.0% PO had 76 or 97% mortality of terrapin scale on peach, respectively. Twigs dipped in 5% SO, CO, or CAO had 89%, 88%, and 96% mortality of terrapin scale. On apple, twigs dipped in 5% SO, CO, or CAO had 98, 100, and 100% mortality of San Jose scale, respectively, compared to 94% mortality for the 5.0% PO treatment.

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Our research has previously shown that soybean oil can substitute for petroleum oil for controlling insects on fruit trees. Soybean oil may also be a safe, environmentally friendly pesticide to use on nursery stock. The objectives of these experiments were to evaluate phytotoxicity of soybean oil to nursery stock and efficacy for mite control. Four replications of container-grown plants of `Alberta' spruce, `Emerald' arborvitae, `Leyland' cypress, Canadian hemlock, and `Andorra' juniper were sprayed on 26 Mar. with 0%, 1.0%, 2.0%, or 3.0% soybean oil; or 2.0% petroleum oil. None of the oil treatments caused phytotoxicity. The same plants were sprayed on 1 Aug. with 0%, 1.0%, 2.0%, or 3.0% soybean oil. Application of 1% or 2% soybean oil appeared to be non-phytotoxic to spruce, but 3% soybean oil caused slight terminal necrosis. Arborvitae, cypress, hemlock, and juniper were not injured by spraying 1% to 3% soybean oil in the summer. Container-grown burning bush plants with mite infestations were sprayed on 20 Sept. with 0%, 1.0%, 2.0%, or 3.0% soybean oil; or with 1.0% SunSpray petroleum oil. Container-grown mite-infested `Andorra' juniper plants received the same treatments, except for the 3% soybean oil. Application of 1% or 2% soybean oil to burning bush or to juniper shrubs resulted in >97% and 87% control of mites 7 and 14 days, respectively, after treatment.

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Soybean oil can be used as an alternative pesticide for fruit trees. Two separate studies were conducted to determine the effects of oil concentration on leaf phytotoxicity and net CO2 assimilation (ACO2 ). In one study, concentrations of 0%, 2%, 4%, and 6% soybean oil in water were applied to individual shoots with a hand-held mist bottle. In the second study, 0%, 1.0%, and 1.5% were applied to whole trees with an airblast sprayer. Petroleum oil was applied as a separate treatment. Net CO2 assimilation was measured on single leaves. Oil residue was removed from the leaf with chloroform, dried, and weighed. Chlorosis and defoliation occurred with applications of 4% and 6% soybean oil. No visible phytotoxicity occurred with 2% or less oil. Net CO2 assimilation decreased as the rate of soybean oil increased from 0% to 4% oil, but there was no difference between 4% and 6%. Net CO2 assimilation decreased with increasing oil concentration from 0% to 1.5% and recovered to the rate of the control on day 7. Net CO2 assimilation was negatively related to oil residue. At an equivalent oil residue, there was no difference in ACO2 between petroleum and soybean oil. Below a residue of 0.15 mg·cm–2, foliar phytoxicity did not occur. Reductions in ACO2 were small and did not last longer than 7 days if residues were ≤0.10 mg·cm–2.

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Soybean [Glycine max (L.) Merrill] oil was applied to apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] as a summer spray in six studies to determine if it controls European red mites [Panonychus ulmi (Koch.)], how it affects net CO2 assimilation (A), and if it causes phytotoxicity. Sprays of 0.5%, 1.0%, and 1.5% soybean oil {TNsoy1 formulation [soybean oil premixed with Latron B-1956 (LAT) spreader-sticker at 10 oil: 1 LAT (v/v)]} reduced mite populations by 94%. Sprays of 1% and 2% soybean oil reduced mite populations to three and four mites per leaf, respectively, compared to 25 per leaf on water-sprayed plants. Soybean oil concentrations of 1.0% and 1.5% applied to whole trees reduced A for less than 7 days. Phytotoxicity did not occur when soybean oil was applied with an airblast sprayer at concentrations of 1.0% and 1.5% or with a mist bottle at 2%. Phytotoxicity occurred when soybean oil was applied with a mist bottle at 4% and 6%, which left soybean oil leaf residues of 0.22 to 0.50 mg·cm-2. No phytotoxicity occurred with 4% SunSpray, which resulted in a mean leaf residue of only 0.13 mg·cm-2. Spraying 1% soybean oil tended to give better mite control than 1% SunSpray Ultra-Fine oil, but caused greater oil residues and a greater reduction in A.

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