Physiological and Physical Effects of Spray Oils on Deciduous Trees

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Abstract
Petroleum oil sprays injure apple leaves by dwarfing or killing whole leaves, and by causing brown, purple, white, dry-green, and oily translucent spots in the leaves. Cresoap is an automatic emulsifier. Ca casemate emulsions of petroleum oils caused translucent angular leaf spots, but cresoap-oil emulsions did not cause angular leaf spots. Oils may kill buds and interfere with proper coloring of fruit. The oils penetrate leaves quickly, and pass between the cells and into the tracheae of the leaves and their twigs. Oils for use on apple leaves should be 83 to 90% un-sulfonatable with viscosities of 70 to 80 sec. Saybolt for most vars. of apples. For dormant sprays on apple, oils should be 60 to 70% unsulfonatable with viscosities of 120 to 220 sec. Proper temps. for application of oil sprays are 40 to 90[degree]F. Oil emulsions may be applied at conc. of 0.5 to 2% oil on leaves, and 4 to 8% oil on dormant buds. Oils decrease transpiration of leaves. Respiration of leaves is increased or decreased by oils depending on the predominance of the chemical or the physical effect. Freezing of oil sprays probably does not change the effect of the emulsions on trees. Effects of oil sprays are variable depending on the spp. or vars. of plants; suffering of plants from fertilizer deficiency, drought, or winter injury; load of fruit on trees; number and cone. of sprays; sulfonatable residues, viscosities, and distillation ranges of oils; condition of buds and leaves; and temperature of air. Improper oil sprays may kill peach leaves, twigs, or whole trees. Tank-mix emulsions must be excellently agitated to be safe on trees.

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