Whiteflies are tiny insects that feed on a variety of plant species, including roses. Both the adults and larvae feed by piercing the surface of rose leaves, then sucking out the juices. While a few whiteflies are not generally a problem, a serious infestation can damage leaves, causing them to yellow and curl, reducing the vigour of your rosebush. In the process, whiteflies produce a sweet waste product, called honeydew, which can attract ants and encourage fungus to grow on the leaves. Some simple steps can help you keep whiteflies from bothering your roses.
Spray your rose plants with a stream of high pressure water from a garden hose to drive away adult whiteflies and dislodge whitefly nymphs attached to rose leaves. Spray the underside of the leaves where the insects tend to congregate.
Release ladybirds or lacewings onto your rosebushes. These insects and their larvae are highly predatory and will feed voraciously on both adult whiteflies and their nymphs. Ladybirds and lacewings are available commercially from mail order or online sources.
Combine an insecticidal soap with water, based on manufacturer directions, in a pump sprayer. Apply the soap to your rosebushes, thoroughly covering the leaves.
Spray a pre-mixed solution of the fungus Beauveria bassiana as another biological control. This fungus infects and kills whiteflies when they come in contact with its spores.
Lay down a reflective polythene mulch around your rosebushes. According to the University of California, this mulch actually repels silverleaf whiteflies.
Apply an insecticide such as acephate, azadirachtin, chlorpyrifos or permethrin as a last resort to eradicate whiteflies if you have an infestation of more than four adult flies per leaf.
Avoid applying insecticides to rose plants after introducing ladybirds or lacewing insects to prevent killing these beneficial insects.