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Four-year-old `Gala' and `Widjit' apple trees with significant apple aphid populations were sprayed to runoff on 13 May 1994 with 0%, 0.5%, 1.0%, or 2.0% (v/v) emulsified degummed soybean oil (SO) or with 1.0% petroleum (dormant) oil (PO). Treatments were arranged in a randomized complete-block design with five single-tree replications. Apple aphid populations were determined on 10 tagged shoots per tree. The top fully expanded leaf of two randomly selected shoots per tree were tagged and net photosynthesis (Pn) and transpiration (Tr) measured. Trees treated with SO or PO had <20% as many aphids after treatment as nontreated trees. Trees treated with 2% SO had lower Pn and Tr than the control for 18 days after treatment. Spraying 0.1% or 0.5% SO caused less initial reduction of Pn than 2.0% SO, and the effect was shorter lasting. Four-year-old `Oregon Spur' and `Empire' were sprayed with 0%, 0.1%, 0.5%, 1.0% SO or PO on 26 June. Treatments were arranged in a randomized complete-block design with four single-tree replications. Pn rates of trees treated with 0.1% to 1.0% soybean oil were <40% of nontreated trees the day after treatment, but recovered to >80% of control in 5 days.
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.
`Redhaven' peach trees at the Knoxville Experiment Station were sprayed to runoff on 3 February 1993 with single applications of 0, 2.5, 5.0, 10.0, or 15.0% (v/v) degummed soybean oil with 0.6% Latron AG 44M emulsifier. Treatments were arranged in a randomized complete block design with 6 single tree replications. The internal CO2 concentration of treated twigs was elevated the first day and continued to be significantly higher than the control through the fifth day following treatment. Respiration rates of soybean oil treated buds-twigs were lower than the control for the first eight days after treatment. Flower bud and bloom development were delayed by treatment of trees with 5.0 to 15.0% soybean oil. Treatment with 5.0% oil delayed bloom approximately 4 days. The greatest delay (approximately 6 days) occurred after treatment with 10.0 or 15.0% oil. Yield was reduced and fruit size increased as the concentration of soybean oil was increased. Optimum fruit size was achieved with the 5.0% soybean oil treatment.
Spurs of `Starkspur Delicious' trees were dipped in 0, 3, 6, 9 or 12% petroleum oil (dormant oil) or soybean oil emulsions on 26 January 1993. The spurs were cooled at 3C/hr until -9C or kept at 21C. After treatment, the flower buds on spurs were forced at 20C for 11 days and then dissected. The cambium and xylem of the spurs and the interior of the flower buds were rated for damage as indicated by browning. The experiment was repeated at the silver tip stage of buds (early March) except that treated spurs were exposed to 20C, -6C, or -9C. Neither the oil treatments nor low temperature exposure caused visual damage to flower buds or cambium in January. However, the oil treatments damaged flower buds at the silver tip stage (March). Neither petroleum or soybean oil caused visible damage to the xylem or cambium of the spurs.
Dormant `Georgia Belle' peach [Prunus persica (L.) Batsch.] trees were sprayed in early February 1992 with single applications of 0%, 2.5%, 5.0%, 10.0%, or 20.0% (v/v) crude soybean oil. `Redhaven' trees were sprayed in February 1993 with single applications of 0%, 2.5%, 5.0%, 10.0%, or15% degummed soybean oil. Additional treatments of two applications of 2.5% or 5.0% oil were included each year. Both crude and degummed soybean oil treatments interfered with escape of respiratory CO2 from shoots and increased internal CO2 concentrations in shoots for up to 8 days compared to untreated trees. Respiration rates, relative to controls, were decreased for 8 days following treatment, indicating a feedback inhibition of respiration by the elevated CO2. Thus, an internal controlled atmosphere condition was created. Ethylene evolution was elevated for 28 days after treatment. Flower bud development was delayed by treating trees with 5% crude or degummed soybean oil. Trees treated with 10% crude or degummed soybean oil bloomed 6 days later than untreated trees. Repeated sprays of one half concentration delayed bloom an additional four days in 1992, but < 1 day in 1993 compared to a single spray of the same total concentration. Application of soybean oil caused bud damage and reduced flower bud density (number of flower buds/cm branch length) at anthesis. In a trial comparing petroleum oil and degummed soybean oil, yields of trees treated with 6% or 9% soybean oil were 17% greater than the untreated trees and 29%more than petroleum treated trees. These results suggest that applying soybean oil delays date of peach bloom and may be used as a bloom thinner.
A factorial arrangement of four replications of ethephon (0, 25, 50, 100, or 150 mg·liter-1) and GA3 (0, 25, or 50 mg·liter-1) treatments in a Randomized Complete Block Design were applied to `Redhaven' peach trees in mid-September. Each tree received the same treatment in 1987-1990. Development of flower buds (after endodormancy completion) was significantly delayed by GA3 and ethephon. The date of 50% bloom was significantly delayed by GA3 (approximately 1 day) and by ethephon (4.7 days with 150 mg·liter-1 treatment). Increasing the concentration of each chemical resulted in more delay of bloom. There was no interaction of the effects of the two chemicals on bloom date. Application of 50 mg·liter-1 GA3 plus 150 mg·liter-1 ethephon caused the greatest bloom delay (6.5 days compared to untreated trees). Gummosis on scaffolds was evident in the fall and following spring on trees treated with the 2 highest rates of ethephon. During the summer and following fall, little gummosis was evident. By September 1991, evidence of gummosis was insignificant and no tree mortality occurred.
Treatments of 0, 10, 20, 30, or 40% (v/v) refined (salad) or crude soybean oil or 0, 5, 10, 15, or 20% petroleum (dormant) oil at 0, 5, 10, 15, or 20% were sprayed until drip on `Smoothee' apple trees on 27 February 1991. The internal carbon dioxide concentration was elevated and the oxygen content reduced within one day in buds-twigs treated with oil and remained influenced for up to 12 days. All oil treatments delayed fruit bud development. The lowest tested concentration of soybean oil (either crude or refined) resulted in the greatest delay in bud development and the greatest delay in bloom (approximately 4 days). Crude soybean oil treatment resulted in less damage to flower buds than petroleum oil.
`Redhaven' peach tree plantings were established in 1985 to compare tree densities (299 trees/ha to 1794 trees/ha) and training systems (Open Vase, Central Leader, Y-shaped, Palmette Trellis, Tatura Trellis, and MIA Trellis). Tree trunk growth (diameter) was significantly less as the population of trees increased. Trunks of trees trained to the Open Vase were larger than Central Leader or Y-shaped trees. In 1988, yields per ha increased as tree density increased. Trees trained to the Tatura Trellis (897 trees/ha) had the highest yields (27.7 t/ha). Trees trained to the Central Leader and planted at 1794, 897, and 598 trees/ha had next highest yields of 24.5, 21.4, and 24.3 t/ha, respectively. By the 6th year, yield differences were not generally related to tree density. The top yielding systems were Open Vase (598 trees/ha) and Tatura Trellis (897 trees/ha) with yields of 32.1 and 29.0 t/ha, respectively. Trees trained to Open Vase had higher yield efficiencies (kg/cm2 limb CSA) in 1991 than trees in other systems-spacings and had yields of 23.6, 27.4, and 32.1 t/ha for plant densities of 299, 448 and 598 trees/ha, respectively.
Tissue cultured `Heritage' raspberry plants were planted in April 1990. Split applications of ammonium nitrate were made to 0.6 m widths on each side of the row at total rates of 0, 22, 45, 90, or 180 kg/ha. Applications were made in May and August in 1990 and in March and July in 1991. The plants were cut to ground level during the winter. In 1990, cane length and number of buds on the central cane were unaltered by N treatment, but all N treatments resulted in the development of more canes than the control and thus more total length of cane growth. Date of 50% accumulated yield was advanced and total yield increased with added N. Foliar N contents (2.35%) of the two highest rates were greater (3 weeks after the second application) than the control (2.12%). In 1991, early yield was slightly delayed by N. Total yield was reduced by the highest N rate. The 45 kg/ha N treatment had the highest yield of 2.53 t/ha. Plants receiving 180 kg/ha had greater foliar N content in June and October than control plants. Soil samples were taken to 30 cm on June 29, 1991. About 80% of the nitrate-N was found in the top 15 cm.
Oil sprays increase the phytotoxicity of captan to apple foliage. The purpose of this study was to determine if oils increase the penetration of captan through leaf cuticles. Enzymatically isolated apple leaf cuticles were used as a model system to study captan penetration. A bioassay was developed using the inhibition of growth of Penicillium cyclopium on potato-dextrose agar as a measure of captan penetration through the cuticle. Captan penetrated through both surfaces, but significantly more penetrated through the abaxial cuticles than the adaxial cuticles. Increasing the captan concentration increased the captan penetration through the abaxial cuticle in a linear relationship. Captan penetration through the cuticle was increased by 63% when cuticles were treated with captan plus 1% emulsified soybean oil. Abaxial cuticles treated with captan plus emulsified soybean oil or with captan plus SunSpray Ultra-Fine oil had >125% greater captan penetration than cuticles treated with only captan. Cuticles treated with captan plus dormant oil (petroleum oil) had 220% more captan penetration than the captan only treatment.