Precautions for Using Petroleum Oil Sprays

Oil sprays are an important component in citrus IPM programs for the control of armored and soft scales, aphids, leafminers, and certain species of mites. When used alone, they may be applied using outside coverage (OC) for aphids, leafminers or mites, intermediate coverage (IC) if used for soft scales, and thorough coverage (TC) if used for armored scales at rates of 1 to 6% depending on the crop, time of year and the target pest. Oils are frequently used at rates of 0.25 to 1% in combination with other insecticides. Because petroleum oils can cause phytotoxicity, the following precautions are important:

• Soil moisture should be maximum before application; spray as soon after an irrigation as the ground will permit operation of the equipment. Be sure to maintain adequate soil moisture from spring throughout the entire irrigation season.
• Do not spray oils when temperatures exceed 95°F or relative humidity falls to 20% or below (in coastal regions, do not spray if the temperature will exceed 85° to 90°F or the relative humidity goes below 30%); also do not use oil sprays immediately before, during, or following an unusually cold weather period.
• Problems of leaf drop and fruit drop can be minimized, in general, by adding 2,4-D to the oil spray mixture. Be careful not to apply 2,4-D within 2 miles of sensitive crops such as tomatoes, cotton, olives, and grapes and do not use 2,4-D during spring to avoid phytotoxicity problems.
• If navel orange orchards are sprayed with oil when oranges are approaching maturity, generally from November until harvest, protection against water spot may be obtained by using gibberellic acid. (Caution: fall oil sprays may increase the risk of damage caused by frost).
• Complete coverage of the tree with an oil spray provides more effective control than increased dosage. If spraying is done by ground, equip the rig with a tower capable of elevating a sprayer 4 feet above the tallest trees.
• Generally, narrow range oils with a 50% distillation range of 415 to 455 are recommended for use in citrus.
• The heavier the oil is (e.g., NR 440 is heavier than NR 415), the better its insecticidal properties will be, but also the greater the potential for phytotoxicity to the tree. The following minimum oils standards were developed in the 1980s, to minimize phytotoxicity:

Minimum Oil Standards Developed by UC Researchers in the 1980s

Specification	NR 415	NR 440
50% distillation point (°F)1	415 ± 8	440 ± 8
10–90% distillation range (°F)2	60	80
Unsulfonated residue, percent3	92	92
API gravity4	32	31
Viscosity, sec.5	70	100
Pour point (°F) 6	20	20

1	The temperature at which half of the oil distills under a vacuum of 10mm of mercury (Hg), also know as the boiling point or midpoint. The ±8°F refers to the sensitivity of the analytical method used to calculate the midpoint, not the variability of the oil specimen.
2	The temperature range at which most of the oil distills (10mm Hg).
3	Minimum percent unsulfonated residue; the actual UR is often higher than 92%.
4	A measure of hydrocarbon composition usually ranging from 31 to 37.
5	Flowability of oil ranging from 60 to 200 seconds. (Unit of measure: SUS at 100°F where SUS = Saybolt Universal Seconds.)
6	Oils with a minimum pour point of 20°F should not be used when temperatures fall below 20°F.

Recent reductions in the sulfonated residue portion of petroleum oils (unsulfonated residues greater than 98%) have allowed higher distillation points to be used in citrus with less risk of phytotoxicity, as long as temperature and moisture conditions are optimal. The higher the distillation point, the greater the control of the insect pest achieved, especially for scale insects. The following table outlines the various properties for oils registered for citrus in California:

Product	Company	Distillation Point (°F)		Unsulfonated Residue (%)	API Gravity	Viscosity (seconds)	Pour Point (°F)
		50%	10-90%
Biocover MLT	Loveland	435	72	99	34.3	70	-5
Biocover UL	Loveland	404	55	99	32.8	60	-5
Glacial Spray Fluid#	Loveland	435	72	99	34.3	70	-5
Narrow Range 415 Spray Oil	Loveland	404	55	99	32.8	60	-5
Leaf Life Gavicide Green 415#	Loveland	404	55	99	32.8	60	-5
PHT 415 Supreme Spray	Britz-Simplot	404	55	99	32.8	60	-5
IAP 415 Summer Spray Oil	Independent Agribusiness Professionals	415	55	98	32.7	57	-15
IAP 440 Spray Oil	Independent Agribusiness Professionals	440	78	98	34.8	70	- 20
Omni Oil 6E#	Helena Chemical Co., TN	407	55	99	32.8	60	-5
Omni Supreme Spray	Helena Chemical Co., TN	438.5	78	98	31.86	83.3	-5
Purespray Green#	Petro Canada	434	80	99	34	76.2	0
Purespray Spray Oil 10E	Petro Canada	408	76	99	34.2	60	0
TriTek#	Brandt Consolidated	438.5	78	98	35.8	68.1	-5
Superior 415 Spray Oil	Wilbur-Ellis	415	55	99	32.8	60	-5
Superior 440 Spray Oil#	Wilbur-Ellis	—	—	—	—	—	—

#	Acceptable for use on organically grown produce.

For more information on oils, see UC ANR Publication 3347, Managing Insects and Mites with Spray Oils (PDF).