Proper plant maintenance can keep whiteflies at bay

Question: I have tiny white insects on the backs of the leaves of my gardenia. When I brush the leaves they fly up into the air like dandruff. What are they?

Answer: The insects you’ve got are most likely a type of whitefly. If you can bring a sample of the insect in to your local extension office or if you have a digital camera and can email a picture of the insect to your local Master Gardener Plant Helpline, we can tell you for sure.

There are several types of whitefly common to gardens in Hawaii, and most become a nuisance in summer months when the weather is dry and hot, so it’s a good idea to address the problem now. Cooler temperatures and wetter weather may bring additional relief.

Q: I have whiteflies on my hibiscus; what can I spray on them?

A: Common household insecticides are not effective in controlling whiteflies. These insects prove resistant to sprays available in local garden centers. Our recommendation is an approach where several methods of control are employed.

Q: I am trying to garden organically and don’t want to spray for whiteflies; what are other methods of control?

A: You’re in luck, because commercial sprays are ineffective against whiteflies. Here are some methods that do work:

» Assess the health of the plant: A healthy plant is able to fight off insects and disease more effectively than is a stressed plant. Publications on individual plants, including gardenia and hibiscus, are available for free from University of Hawaii’s College of Tropical Agriculture and Human Resources website — www.ctahr.hawaii.edu/site/info.aspx — and will explain in detail the needs of the plant. Make sure the plant is receiving adequate moisture and fertilization, and that the soil has been amended to sustain a healthy environment for the plant.

» Check the level of damage to the plant. If the whiteflies have caused little damage, it’s best to just physically remove the insects from the leaves by spraying with a high-powered hose, or simply use a wet paper towel or sponge to wipe them off.

» If there is a heavy infestation, it’s best to prune the plant, removing the branches that are most affected. Neem oil (which is considered organic) or insecticidal soap can be used to keep infestation levels low; however, the use of these insecticides alone will not resolve the situation. Keeping the plant healthy according to recommendations, physically removing the insects or pruning highly infested branches, and monitoring for future infestations will bring the most success.

Q: I heard that insects are attracted to different colors; is that true?

A: Surprisingly, yes. While coffee berry borers prefer the color red, research has shown that whiteflies are attracted to yellow. Yellow sticky cards can be purchased at your local garden center, sometimes labeled as fly tape.

Or make your own: First, take yellow card stock paper and cut into 3-by-8 1/2-inch strips. Second, spread Tanglefoot pest barrier or petroleum jelly onto the strips. Staple strips covered in sticky adhesive to a wooden stake and place close to the plant with white fly infestation. The yellow strips attract the adult whitefly, ultimately disrupting its life cycle and reducing its ability to reproduce.

For the Master Gardener Plant Helpline in your area, visit www.ctahr.hawaii. edu/UHMG or call 453-6055 on Oahu.