Questions and Answers on Spray Oils
Part I - Chemistry
1. Q. From what are spray oils derived:
A. Spray oils are derived principally from the lubricant portion of petroleum.
Animal oils have been used, but to a lesser degree.
2. Q. Of what are spray oils composed?
A. Spray oils are composed essentially of hydrocarbons - compounds containing
hydrogen and oxygen.
3. Q. What three classes of hydrocarbons occur in spray oils?
A. The three classes of hydrocarbons found in spray oils are:
1. the paraffin chains
2. the aromatic rings
3. the napthene rings
4. Q. Why is it important to know which classes of hydrocarbons are present in the oil?
A. The percentage of each structure class in any oil has an important bearing on both insecticidal efficiency and plant safety. Paraffin chains have the highest insecticidal value and plant safety, the napthene rings have a lower insecticidal efficacy, and the aromatic rings are the toxic structures.
5. Q. What two factors affect the insecticidal value of an oil? How?
A. The insecticidal value of an oil is affected by its paraffinic content and by the size of its molecules. The efficiency of an oil increases as the paraffinic content in the oil increases. The length of time an oil remains on the insect or on the foliage depends greatly upon its molecular size.
6. Q. What criteria are used to indicate the molecular-size property of an oil?
A. Viscosity and boiling range data are the criteria most commonly used to indicate the molecular size of an oil.
7. Q. What happens if the molecular size of an oil is too small? too large?
A. If the molecules of an oil are too small, the oil may evaporate before its suffocating effect on the pest is complete, resulting in poor control. If the size is too large, the oil may remain on the foliage longer than is needed for the good pest control and its mechanical presence may interfere with the normal functions of the plant resulting in poor fruit color and lower soluble solids.
8. Q. What determines the safeness of spray oils to plants?
A. The safeness of spray oils to plants is related to the aromatics and other unsaturates present. These are the ingredients that kill plant tissue. Oils can be made increasingly safer to use on plants by lowering the aromatics ring content.
9. Q. How can the aromatics and other unsaturated structures be removed from an oil?
A. The aromatics and other unsaturated structures in an oil can be removed in part by refining operations by treating the oil with strong sulfuric acid. These structures react with the acid to form sulfonates, which can be separated from the remainder of the oil.
10. Q. What does the term UR mean?
A. The term UR or unsulfonated residue is used to indicate the degree of refinement of an oil or its freedom from unsaturates of impurities. Oils intended for foliage sprays have UR values ranging from 84 to 96. An oil with an UR of 84, for example, would be 84 percent pure oil and 16 percent impurities. An oil with a UR of 96 would contain only 4 percent impurities.
11. Q. What is a white oil? a red oil?
A. Oils with a high UR, 92-96, are referred to as white oils. Oils with a low UR, referred to as red oils, are, in a sense, simply insecticide oils diluted with non-effective fractions or impurities and consequently greater strengths are needed.
12. Q. Why not remove all the impurities in an oil?
A. A matter of economics - as the UR of the oil increases above 80 the more costly the refining operation becomes and when a UR of 96-98 is reached to proceed further would be too expensive to consider.
13. Q. How can the knowledge of the chemistry of oils help a sales representative?
A. The knowledge of the chemistry of oils can help the sales representative in several ways:
1. To help answer customer questions
2. To help clarify the controversy or misunderstanding of spray oils
3. To help understand why spray oils should be referred to as individual products and not as a common class 4. To help provide sales points for "VOLCK" oils.
Part 2 - Mode of Action of Oils
14. Q. How does oil kill? A. Sprays oils kill insects and mites by what appears to be essentially a smothering action. By enveloping the pest with a continuous film of oil
A. interferes with the breathing and excretion processes and ultimately causes death by suffocation and uremic poisoning.
15. Q. How long does it take for oil sprays to kill armoured scale?
A. The period required for oil sprays to kill scale varies - longer in the winter months when the scales' metabolic rates are slow, and faster in the summer months when its life processes have speeded up. As a rule, one should not attempt to check for kill of armoured scale in the field with low power magnifying glasses until at least four weeks after oil application.
16. Q. How does the oil contact a scale under its armour?
A. The usual route of the oil is under the armour from its edges. Some oil may penetrate directly through the armour, but this is slight.
17. Q. Why do oil sprays often fail to control severe infestation in which the scale have piled up?
A. The route of an oil under the edges of the armour points out the reason for failure of oil sprays to completely control piled up scale. The outer layers of scale in the pile will prevent the oil film from contacting the inner-most scale in the pile, and as a result control will not be complete.
18. Q. Why will an oil spray of minimum oil strength often control light infestations of scale but fail to control heavy infestations even though not piles up?
A. This is what I like to refer to as competition or competitive activity. With minimum oil strength and a few scale each scale may still get a lethal dose of oils with minimum oil strength and numerous scale, each scale is competing for the oil and all may get a sub-lethal dose and none a lethal dose. The competitive activity is also involved when wettable powder formulations are combined with oils and when foreign matter is present on the sprayed leaves.
19. Q. How does oil control scale crawlers?
A. Besides killing the scale crawlers that it contacts, an oil film on the plant interferes with the successful establishment of the young that may hatch after treatment.
20. Q. Why is through coverage important in the use of oil sprays?
A. The mode of action of oil points out the importance of thorough coverage. The pest must be contacted if its is to be controlled.
Part 3 - Phytotoxicity of Oils
21. Q. What determines the safeness of an oil to plants?
A. The safeness of spray oils to plants is related to the aromatics and other unsaturated structures present. These are the impurities that kill plant tissue.
22. Q. In addition to killing of plant tissue by the impurities present in the oil, what other ways might oils affect plants?
A. Oil readily enters the openings or stomata of the leaf. In citrus foliage the oil may penetrate both sides of the leaf. The oil then passes into the air spaces of the leaf and from there into the conducting vessels. Depending upon the amount of oil applied, the physical properties of the oil, the temperature, and the moisture content of the leaf both respiration, or food manufacture, and transpiration, or loss of water, may be reduced by the mechanical presence of the oil.
23. Q. How do oil sprays affect fruit color and maturity of citrus?
A. The mechanical presence of the oil and its affect on food manufacture may delay fruit color and maturity. The toxic fractions in the oil may have a more permanent effect on color and maturity. It has been shown that an oil spray with a high UR value and such molecular size as to remain only for the period necessary for good control will have less effect on color and soluble solids in citrus fruit then an oil with a low UR value and a slow evaporation rate.
24. Q. Explain the relationship between oil sprays and leaf drop?
A. The mechanical presence of the oil, unless excessive, does not kill leaf tissue or cause leaf drop. Leaf drop is caused by the toxic fractions left in the oil in the refining operations and shown in terms of UR. On mature leaves that are forming abscission layers the mechanical presence of the oil in the already partly plugged conducting vessels may completely plug these vessels and cause leaf drop.
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