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Index : Pests
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- 9. Whiteflies Attacking Acacia Trees - Top
- Sweet acacia trees in the Tucson area are being attacked by a tiny sucking insect called the acacia whitefly. As the name implies, the adults are tiny white winged insects covered with a white powdery substance. Many acacias are so heavily infested that shaking the limbs results in a white cloud of the insects hovering through the trees.
The adult acacia whiteflies lay eggs on the acacia and the eggs hatch into an immature form of the insect called a nymph. These nymphs are black in color, about the size of ground pepper, and are attached to the upper side of the leaves. Under magnification, these nymphs resemble small rounded black shells with white fringe protruding out from the edges of the shell.
The nymph develops into a pupa within the shell or case. The pupa develops into the adult whitefly that emerges from a slit cut in the case. The adult whiteflies mate and lay eggs which begins the process all over again.
All stages of acacia whitefly, from nymph to adult, suck fluids from the leaves and secrete a sticky substance known as "honeydew". The honeydew looks like clear, shiny varnish coating the stems and branches. Over time the insect feeding causes leaves to appear dull green, then yellow in color. As the feeding continues the leaves turn brown and die.
The attack of whiteflies on acacia will not kill the trees, but it will cause them to be unsightly and partially or totally defoliate. This could cause problems, especially if shade requiring plants are growing underneath the acacias.
It is possible to control whitefly and lessen their damage by spraying trees with a soapy spray using dish washing detergent. Mix up a soap spray solution by adding two tablespoons of liquid dish washing detergent in one gallon of water. Do not use lemon-scented soaps as the fragrance can be harmful to some plants.
Apply a fine mist of spray to the leaves. Be sure to spray the underside of leaves as well as the top. It's a good idea to come back a week later and spray the tree again. The soap residue should not to be rinsed off the leaves. The recommended amount of soap is so mild that it won't hurt your tree, unless your spraying constantly. At this time of year, only spray in the early morning between 4:00 and 8:00 a.m. when temperatures are at there coolest.
Soap spray will not eradicate the whiteflies, but it will kill a substantial number of them, enough to keep the damage to a minimum. If rain occurs the day that the soap spray was applied, spray the tree again the following morning. To keep the whitefly in check may require periodic spraying. After the two initial spray, monitor the tree(s). If whiteflies numbers build up again, resume spraying.
A different type of whitefly attacks many types of flower and vegetable plants. It's called the greenhouse whitefly and is also present in the Tucson area at this time of year. Soap spray is also recommended for the control of greenhouse whitefly. But unlike the temporary damage inflicted on trees by the acacia whitefly, the greenhouse whitefly can kill flower and vegetable plants if left uncontrolled.
Greenhouse whiteflies can be difficult to detect in the early stages. Unlike the acacia whitefly, nymphs of the greenhouse variety are not black, but transparent to light green in color and blend with the color of the leaf itself. But the whitefly adults are white and are easily seen when disturbed, flying about the infested plants.
Finally, if frequent rains occur this monsoon season it will help control certain insect pests such as whitefly. In addition, spider mite, aphid and leafhopper populations will be held down. Inspect plants on a regular basis to determine if pests are present and doing injury to your plants. Soap sprays will effectively control most of these sucking insect pests.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161. - Updated: July 11, 2004
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