Hidden Valley Hibiscus ~ Hibiscus Pests

Whiteflies

There's a White, Sooty Stuff all over my Hibiscus!

These little pests have long been the bane of gardeners and greenhouse growers alike. Once they settle into a garden they can be very hard to get rid of.  Then along came the Giant Whitefly, up from Mexico into California, and now spread throughout the south all the way to Florida. Though its name sounds menacing, it is only "giant" relative to other whitefly species. What makes the impact of the Giant Whitefly so large is the amazing mess it can make, covering a plant with ugly "beards" made up of white waxy filaments. As difficult to get rid of as these pests were in the past, they are now easily controlled, as we will describe below.

How do I Know if I Have Whiteflies?

Whitefly Egg Mass Showing On Underside of Leaf

To see if you have whiteflies, all you have to do is shake your hibiscus plant. Whiteflies feed on the underside of leaves, and a good shake of the main stem will send them flying out in a cloud of visible white flying insects. They will fly off for a short time only to settle back down on the same plant or a nearby one. They are bright white in color but otherwise look and fly more or less like small houseflies. As they feed and reproduce on the host plant they excrete a sweet honeydew that is quite sticky to the touch. Black sooty mold spores land on this honeydew and grow there, covering the leaves with black mold.  This mold does not attack the plant but is very unsightly and blocks the sunlight from the leaf it is growing on. It does wash off with forceful water sprays although it may require some scrubbing to remove it completely. A soap and oil mixture, such as our Clean Leaf Spray can help remove the mess off you leaves, followed by a thorough spraying on all sides of the leaves with water with a hose or a BugBlaster.

Off-Color Bud A Bad Whitefly Infestation on a Hibiscus, Leaves Covered with White Wax and Honeydew

The Giant Whitefly can be detected in the same way as the other whitefly species, but if it is not caught early the signs of it will become impossible to ignore.  Spirals of white wax will be deposited on your hibiscus by adult whiteflies as they walk on leaves. When populations of the giant whitefly reach high levels, the insects and their waxy deposits can be seen on both upper and lower leaf surfaces. Eggs are often laid among the wax deposits. After hatching, the nymphs produce long, hairlike filaments of wax up to 2 inches long that give a bearded appearance to affected leaves.  The overall result of all this wax production is a messy, dirty appearance and a weakened plant.

How do I Get Rid of Whiteflies?

Whiteflies exhibit a strong tendency to feed in groups. After adults emerge, the majority will remain on the same plant to feed and lay eggs. They do spread from plant to plant, and the range of hosts includes not only hibiscus but also other popular garden species such as bougainvillea, bamboo, mandevillea, begonia, giant bird of paradise, orchid tree, banana, mulberry, xylosma, aralia, and various vegetables as well as some varieties of citrus and avocado trees. 

Using a BugBlaster to Spray off Whitefly Mess

Since whiteflies have such a wide range of hosts it is important to inspect all the plants in your garden and to treat all that have whitefly infestations. In some cases it is most effective to treat all plants in an area, whether they show whitefly signs or not. Before pesticides are used, it is possible to drive whiteflies away by forceful water sprays. We have done this successfully when the whiteflies have recently infested a plant and are not well established. You can also slow down an invasion by removing and disposing of the individual leaves that the whiteflies are feeding on. However, once the infestation is established, more effective measures are called for. One is spraying the leaves top and bottom with soap and oil mixtures, such as . Not only does this help clean the leaves, but it smothers and dehydrates insects that are sprayed directly by the mixture.

If water sprays and removing leaves that whiteflies are growing on does not solve the problem, there is excellent pesticide control available. Even better news is that this pesticide is not sprayed on the plant but instead is poured into on the soil in the pot or over the root zone of plants in the ground, making application easy and safe. The new, and relatively non-toxic active ingredient, "imidacloprid," eliminates whiteflies from garden or home. Some of the brand names that contain this ingredient are Bayer Tree and Shrub Insect Control, Merit, and Marathon.  This pesticide is systemic, which means that it is absorbed into the plant where it remains in the sap for months. Whenever a whitefly or other sap sucking insect feeds on the plant, it is killed by the imidacloprid in the sap. This is the same active ingredient now found in some dog flea products - it is not very toxic to people or pets but is deadly to many insects. It is best applied before the problem becomes severe and can be reapplied when the effect wears off, every 6-12 months. For a severe infestation, you may need to apply the product twice at 3-month intervals to get complete control over the infestation, then switch to a maintenance application schedule of once or twice a year.

Word of Caution

If spider mites are present at the time imidacloprid is applied, it will stimulate more rapid egg laying by the mites. To control mites it is necessary to spray water, Clean Leaf or Bayer Advanced 3 in 1. See our new Spider Mite Page for more information about identifying and treating spider mites on your hibiscus.

Resistant Whiteflies

A Healthy Heaven Scent Bush

Whiteflies of all species have been heavily sprayed by farmers and nurserymen for decades and many species have become resistant to the older insecticides. This can, and probably will, happen with imidacloprid eventually. In fact, some nurseries are already finding that to be the case. If you are unfortunate enough to encounter resistant whiteflies that no amount of imidacloprid can get rid of, you will have to go back to the basics. Water or water with soap and horticultural oil are quite effective if applied to all plant surfaces. Insects do not become resistant to these since their action is not chemical. Just spray the oil and soap product every 3 days for 2 weeks (4 applications) and whiteflies will disappear. The advantage of the systemic pesticide is that not only does it get rid of current infestations but it prevents new insects from infesting the plants for weeks or even months.

Whiteflies are no longer the scourge that they once were. Modern pesticides, as well as good old-fashioned soap and oil sprays, make controlling them fairly simple. A treatment of imidacloprid in early spring and another in mid-summer, or whenever whiteflies become a problem, should take care of this pest. Soap and oil sprays require more work and more applications but are safe and effective as well.

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