Hibiscus Plant Care


There are Little Specks all over my Hibiscus!

Aphids, sometimes called plant lice, are a common insect pest for hibiscus. They are visible to the naked eye and come in a rainbow of colors - black, white, and green being the most common ones on hibiscus. People who study insects tell us that there are about 4,000 different aphid species - 250 of them pests of important commercial plants.

Black Aphids on a Hibiscus Bud
Black Aphids on a Hibiscus Bud
You will usually see aphids on hibiscus close to the tops of the stems. Often they congregate on and around the flower buds. Besides being large enough to spot easily, they also excrete a substance called "honeydew" that is clear and sticky. This drops onto the top of the leaf below where they are feeding and very quickly a type of mold called "black sooty mold" grows in the honeydew. The black color stands out on hibiscus leaves and its presence tells you that a sap-sucking insect such as aphids is feeding on the plant. (There are other sap suckers such as white flies that excrete honeydew, but aphids are the most common.)

Aphids feed by inserting a sharp beak called a "stylet" into the leaf, puncturing a phloem vessel which is like a blood vessel in mammals, except in hibiscus it carries the water, carbohydrates, and proteins that plants use. This "sugar water" is under pressure inside the vessel, so once it is punctured by the aphids mouthparts the liquid flows into the insect.

Aphids can reproduce very quickly, and if uncontrolled will increase in number amazingly fast. Since they tend to feed on the plant they were born on, they can quickly weaken a plant and cover its leaves with honeydew and black sooty mold that prevents sunlight from reaching the leaf. In addition, aphids can spread plant viruses to the plants they are feeding on.

Aphids have several natural enemies that feed on them, and if these are present in large enough numbers, the population of aphids is kept under control. Ladybeetles (Lady Bugs) and Lacewings are two of the predator insects that feed on aphids; however, it is not uncommon for aphids to reproduce at rates faster than natural predators can consume them.

The reproduction of aphids is strange and fascinating. Typically it goes like this: One or more eggs laid in fall will overwinter on a leaf. In spring when the weather warms up, that egg will hatch. All the newborns will be females, and those females will give live birth (not eggs) to baby aphids that are genetically identical to themselves without any involvement with a male aphid. Within a few days, these new females will also begin giving live birth to more genetically identical females. In this way aphids may go through 40 generations of reproductions within one summer. This can result in literally billions of aphids unless some are killed by predators or human intervention. In the Fall, as the temperatures drop, winged males are born. Females mate with these males and then lay the eggs that are overwintered on leaves. When food supplies dwindle winged females are born. These then migrate to other plants where the whole process begins again.

How to Control Aphids?

Green Aphids on a Hibiscus Bud
Green Aphids on a Hibiscus Bud
Due to this very efficient way of reproducing, aphids need to be controlled when they are first seen on your hibiscus. The very best way to do this is to treat the plants with a systemic pesticide that enters the hibiscus through the roots, and is then circulated within the phloem vessels of the plant for several months. When an aphid pierces the phloem vessel and feeds on the sap inside, it also ingests the pesticide and dies.

We offer two products that control aphids. The easiest to apply and longest lasting is Bayer Rose & Flower. This is sprinkled on the soil then watered in, and lasts 3 months. We also have Bayer Advanced 3-in-1, a spray pesticide that needs to be repeated every 2-3 weeks if aphids are active and present. For this reason, in our own use at HVH, we find the systemic product, Bayer Rose & Flower to be by far the easiest and most effective pest control product to control aphids.