Use of Oils to Manage Insects

The use of oils as part of a control program is becoming more favored instead of using synthetic pesticides. Oils can be distilled from petroleum such as horticultural oils, Volck oils, summer oils, dormant oils or mineral oils or oils can be extracted from plants and animals such as neem oil or fish oils. Oils are generally effective against aphids, scale crawlers, mealybugs, spider mites, whiteflies and small caterpillars.
When oils are applied, a thin layer covers the insect or mite. The oil clogs the spiracles or pores through which they breathe causing death by suffocation. Oils can also disrupt membrane function or structure or disrupt feeding. Multiple applications may be needed for control.
Sometimes oils can injure a plant causing leaf scorching, defoliation, reduced flowering and stunted growth however there are some items on the label to be aware of such as unsulfonated residues, viscosity, and distillation. Usually the higher the unsulfonated residue (UR), the less likely for plant injury. Also the lower the viscosity, the less likelihood for plant injury. In addition, the distillation range is a measure of the purity of the oil fraction so distillation ranges of 80°F or less are considered appropriate.
It is best to apply oils when conditions are lower than 85°F and 90% humidity is recommended, since the longer the wet oil remains on the foliage, the greater the chance of phytotoxicity. Also it is not advised to treat stressed plants with oils and some plants are sensitive to oil such as azalea, hibiscus, impatiens, photinia, and spruce so they should not be treated.

Whiteflies on Houseplants

The silverleaf whitefly is the most economically important whitefly species in Texas, with a host range of more than 500 plant species, including poinsettias. Adults are 1/16 inches in length with white wings and pale yellow bodies. They will flutter around when disturbed and tend to be more active during the late morning and afternoon, compared to early morning and evening.
The female whitefly will lay oblong, smooth, yellow to amber-brown colored eggs randomly on the underside of leaves. The eggs hatch into flat, greenish-yellow, oval nymphs that begin to suck the sap of plants. Both the nymphs and adults remove phloem from leaves, which causes the leaves to turn pale and die or drop off. Since whiteflies remove phloem, they also excrete honeydew. This honeydew is a perfect media for sooty mold to grow. In addition, plant disorders and virus transmission can result from whitefly feeding.

Some Suggestions for Control Options:

Some Non-Chemical Control Options:

1) Inspect new plants before purchase and treat any infested material.
2) Remove and destroy heavily infested plants from the landscape or interiorscape.
3) Introduce and preserve natural enemies, such as ladybeetles, green lacewings, minute pirate bugs, big eyed bugs and damsel bugs that are predators of whiteflies and minute wasps, such as Encarsia formosa and Eretmocerus eremicus are parasitoids of whiteflies.
4) Beauveria bassiana, a fungus sold commercially can be used to control whiteflies.

Some Chemical Control Options:

Insecticide misuse can result in whitefly populations that cannot be controlled, since chemical overspray can lead to whitefly resistance. Several classes of insecticides are labeled for use against whiteflies and these classes should be rotated in order to avoid resistance. Systemic insecticides can be used such as those containing imidacloprid, dinotefuran or thiamethoxam. Also insecticidal soaps and horticultural oil can be used.

Picture of whitefly. Photo by Dr. Scott Ludwig, Program Specialist-IPM, Texas AgriLife Extension, Texas A&M University System.