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Index : Pests
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- 13. What's That - Top
- Occasionally gardeners notice some pretty strange looking white stuff on their plants. It might look foamy white, or it could appear cottony or powdery white. All this white ‘stuff' is actually produced by three distinct little insects that can, from time to time, find there way on your plants.
The first and probably most common is the white cottony substance, produced by cochineal scale. The cotton is a waxy substance secreted by the insect underneath, a tiny, bright red soft-bodied scale. It is exclusively found on prickly pear cacti.
Damage to the prickly pear is caused by the drawing out of fluids from the cactus pads by the scale insects. The greater the number of scales, the more damage to the cactus. Most of all, the globs of white cotton masses on the pads can become very unsightly.
If pads are heavily encrusted with the cottony wax, it's best to remove the pads by cutting them off at the base with a hand pruners. In some cases this may require removing most of the pads and allowing the cactus to re-grow. If the infestation of cochineal scale is light, you can save the pads by spraying away the protective wax with a hard spray from a garden hose nozzle. After the pads dry, a soap solution can be sprayed on the now exposed scale to kill them. An effective soap solution can be made by mixing two tablespoon of liquid dish washing detergent in one gallon of water.
The second most common white stuff on plants is called "spittle". As the name implies it is a white, foamy, frothy glob which looks like spit! It is commonly found on rosemary, sage, and juniper, but can also appear on a host of herbaceous plants. Numerous spittle globs can appear on an infected plant. The spittle itself is actually a mixture of a liquid goo and air bubbles secreted by the underlying spittle bug nymph. The spittle coats the nymph, providing protection from predators. In time, the nymphs mature into small, winged adults that fly about looking for host plants to lay their eggs.
Although rather unsightly, spittle bugs do little damage to plants. Nymphs and adults feed by drawing fluids out of leaves and stems, however, not enough to cause serious injury.
In addition to providing protection from predators, the spittle provides thermal control for the nymphs. The bubbles insulate them from heat and cold, and the goo protects them from moisture loss. Hosing off the spittle will leave the nymphs unprotected and offers the best control. Without the mass of spittle surrounding them, these insects will quickly dry out and die. If new eggs hatch and nymphs develop, just hose off the newly formed spittle.
Finally, if the white splotches on your plants are not foamy or cottony, but white and powdery with a soft pink underbelly, then you have mealybugs! Mealybugs are most commonly found on succulent houseplants like jade and kalanchoe. Outdoors, they most typically show up on citrus and other fruit trees, and strangely enough, desert spoon.
Unlike cochineal scale and spittlebug nymphs, mealybugs move about on the plant, all- be-it slowly. They often cluster together at the base of stems and along branches. They are oval in shape, about one-quarter to one-half inch long, covered with white powder on top with white filaments radiating out from around their body.
Mealybugs can inflict serious harm to plants, so strong control measures are necessary. One of the safest materials for control of mealybugs is Neem Oil. It is a naturally occurring compound extract from the Neem tree that kills mealybugs on contact. In additions, Neem Oil also controls other soft-bodied insects such as white flies. A closely related product derived from the Neem tree, called Neemix, will also control mealybugs. You can find either product at most places where garden supplies are sold.
"Getting Started with Bonsai" is the topic for this week's garden demonstrations. They will be presented on Wednesday at 9 a.m. at the Pima county Extension Center, 4210 N. Campbell Ave; and at 1 p.m. at the Wilmot Library, 530 N. Wilmot Road; and again on Thursday at 2 p.m. at the Marana Planning Services on the Northeast corner of Orange Grove and Thornydale.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: April 27, 2003
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