Mineral oil has been used as a pesticide in agriculture since the 1920s ― mostly on citrus to control scale insects and greasy spot disease. The general consensus amongst researchers has been that the mode of action of mineral oil as an insecticide is by suffocation of the pest.

Research within the past 10 years however has opened the door to a new understanding of how mineral oil affects insects. Research now indicates that mineral oil can also modify certain plant feeding insect behaviors such as feeding and egg laying. Insects vulnerable to behavior modification from contact with mineral oil include ―

How Could Mineral Oil Affect Insect Behaviors?
It would seem plausible that many plant feeding insect species would be vulnerable to the behavior modifying effects from mineral oil. The exact mechanism by which this occurs is not known but is most likely physical (hence, resistance should never develop) and probably quite simple.

We do know that plant feeding insects have evolved host detection mechanisms. In order to feed or lay eggs on a host plant, insects must first detect a host plant at the chemical level. This is accomplished by use of tiny, hollow  hairs (called sensillae, see photo opposite) located on their mouthparts, feet and abdomen. Each hair has a small canal which opens to the outside through a microscopic pore (as small as one-millionth of an inch).

Inside the canal are nerve endings which are stimulated by specific chemicals (called secondary chemicals) produced within the host plant and are detected in the process of probing. Contact with these secondary chemicals can trigger or stimulate an insect to feed or lay eggs at specific locations within the plant. Plugging these pores would effectively ‘blind’ the insect from commun- icating with its primary food source or egg laying site.

Are Beneficial Insect Behaviors Affected, Too?
Over the past 20 years we have seen abundant evidence that beneficial insect behaviors are not affected by Stylet-Oil applications. As a prime example, on cucurbit crops treated twice per week with Stylet-Oil in Central America and south Florida we have consistently observed high rates of parasitism of leafminer larvae as well as development of all 4 stages of lady beetle and lacewing predators.

We believe the reason beneficial insect feeding and egg laying behaviors are not affected by Stylet-Oil is because these insects have evolved a totally different set of host detection mechanisms. In lieu of plant sensing sensillae, beneficial insects have evolved mandibles, ovipositors, claws and large eyes to detect and catch their prey.

Disruption of an insect behavior can be a powerful tool in the hands of a competent grower. By managing behavior (preventing eggs) early in the first population cycle there is a high likelihood that future generations will be significantly suppressed making it possible for beneficial insects to forage and develop at the same time oil is being applied. Though contact with sufficient oil can suffocate beneficial insects, we have not seen evidence that oil significantly impacts beneficial populations.

The Need For Quality Spray Coverage:
Stylet-Oil is not a systemic chemical, thus performance of the oil is directly related to the quality of the spray coverage. When spraying Stylet-Oil as an insecticide, spray equipment should be optimized to target insect resting, feeding and egg laying sites early in the growing period and / or sprayed immediately before egg laying periods.

For control of pests on the under leaf surface of row crops (such as whitefly and mites) we recommend using small orifice spray nozzles in combination with high spray pressure. For row crops we have found that a hydraulic boom sprayer operated at 400 psi spray pressure using Albuz lilac color ATR or HCA green color ceramic hollow cone nozzles to be superior to air assist or electrostatic sprayers.

However, the dynamics change when spraying on a large spray target such as orchard trees or hop. Here the orchard or air assist sprayers are superior. Growers can check for quality of coverage as well as persistence of oil by immersing oil-sprayed leaves into water (see photo below). Water will bead on plant surfaces which have been sprayed with oil.

To Enhance Thorough Coverage:
Thorough coverage of fruit bunches and foliage is necessary for optimum performance. To enhance thorough spray coverage:

• maintain a constant sprayer speed
• if necessary, remove excess foliage during the season so the spray can reach fruit bunches
• check nozzles for wear before and during the season. Replace worn nozzles when they eject 10% more gallonage than new nozzles
• spray every row, never alternate rows
• do not spray when wind speed exceeds 10 mph or apply the oil to wet foliage
• vary the volume of dilute spray according to the size / density of the spray target
• spray to the point of runoff

Method of Application
Type of Sprayers Used to Apply Stylet-Oil:*

• orchard or speed sprayer
• air assist
• Kinkelder electrostatic
• hydraulic boom sprayer

* Do not use low volume sprayers (such as mist blowers or low volume electrostatic sprayers) because coverage will be compromised from lack of dilute spray volume.

Spray Pressure: Spray pressure may vary depending on the type of sprayer used. Consult the current label. When using conventional application equipment (hydraulic boom sprayer), spray for coverage of the upper leaf surface.

Tractor Speed: Tractor speed may vary depending on the type of sprayer or crop being sprayed. Adjust tractor speed to achieve thorough spray coverage to the point of runoff. On large fruit trees, the tractor speed may be 1 to 2 mph; on row crops it may be 3 to 4 mph.

Agitation: Use constant agitation in the spray tank. Use either mechanical or bypass agitation to insure the oil remains an emulsion in the tank. Never leave a spray tank of oil + water overnight to be sprayed out the next day.

For Greenhouse Use: Apply recommended rate for control of the greenhouse pest. Spray at no less than 400 psi spray pressure using ceramic spray nozzles. Use Albuz ATR lilac color or HCA green color nozzles or their equivalent. Apply weekly or every 2 weeks depending on the level of pest infestation. From 20 to 100 gallons of dilute spray emulsion per acre, depending on plant size. Spray to the point of runoff. Vary quantity of spray applied by changing the number of nozzles used, not by changing spray pressure or speed of sprayer (see Spray Programs, Greenhouse Crops).

Application Rate and Spray Frequency
Concentration: Rate may vary depending on the pest or crop ― consult the current label. Growers should monitor level of infestation and use a higher rate when the label specifies a concentration range (for instance, 1 to 2 %) and pest pressure is severe.

Gallonage: Consult the current label. From 20 to 100 gallons of dilute spray emulsion per acre depending on plant size. Growers should adjust gallonage according to the size / density of the spray target to achieve thorough coverage.

Gallonage Should be Adjusted By:

• adding or removing spray nozzles
• changing the nozzle orifice tip size
• on large fruit / nut crops by adjusting tractor speed

We do not recommend adjusting spray pressure to change the gallonage as this will affect the size of the spray droplet and possibly compromise coverage.

Spray Frequency: Spray frequency may vary depending on the crop or level of infestation ―  consult the current label. Spray weekly or once every two weeks depending the level of infestation.

Re-Entry Interval ― The re-entry interval (REI) for Stylet-Oil is 4 hours.
Residue Tolerance ― Stylet-Oil has no residue tolerance.
Pre Harvest Interval ― There is no pre harvest interval.