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Index : Pests
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- 10. Fuzzy White Lines on Plant Stems - Top
- White fuzzy lines or patches on stems of many types of herbaceous and woody plants is not powdery mildew fungus or some type of mold growth. It is the secretion of a small insect called a plant hopper.
Plant hoppers are small sucking insects, usually too small to be easily seen. They feed by sucking the fluids out of leaves and stems. Unlike aphids, mealy bugs and other types of sucking insects, their feeding causes no detectible damage. What is notable and noticeable is a white wax or flocculent they leave behind on the stems of a wide range of soft-stemmed garden plants and the new shoots of many trees and shrubs.
The white wax secretion of plant hoppers runs in lines along the stems of effected plants. If you were to pull back this wax and look at the stem under a magnifying glass you would see a small cut or cuts made in the stem. These cuts are made by the female plant hopper into which she lays her eggs. Then to seal and protect the eggs until they hatch, she produces a white wax to cover and seal the cuts. It's this wax that's apparent on many plants from spring through fall. The eggs eventually hatch and the young nymphs set out to feed on leaves and stems, eventually to mature, breed and lay more eggs.
The stems of flowers and vegetables are a favorite of the egg laying female plant hoppers, but almost any type of soft stem that can be easily cut is fair game. Plant hoppers prefer herbaceous plants; flowers, vegetables and herbs. Desert plant varieties are not usually effected. It's mostly the lush introduced garden and landscape plant species that are flocked by plant hoppers.
Since they don't do any real damage to plants, no control of plant hoppers is recommended. In a short period of time the white wax on stems wears away or is washed off by monsoon rains.
The large masses of white wax that appears on the pads of some prickly pear cactus is not the flocculent of plant hoppers, but it too is insect related. In this case the wax comes from an insect common to the Sonoran desert called cochineal scale.
Cochineal is a tiny red sucking insect that draws the fluid from pads of prickly pear. As the feed, they produce masses of a white waxy material as a coating to help protect them from predatory insects and birds looking for a tasty meal. If you pull through the wax with a pencil or ice pick you'll encounter the red cochineal scale insects.
Unlike plant hoppers, cochineal scale can do significant damage to the prickly pears they are feeding on, so control measures are advised. Pads that are heavily covered with wax and scales should be pruned off and removed. Prune where the joint of one pad meets another. Don't remove just part of the pad by cutting it in two. 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.
Of special interest about the cochineal insect is the fact that it was used by the early Aztecs as a dye. In the1500s Cortez introduced cochineal dye to Europe and it soon became the favored red dye for everything from fabrics to paintings. Cochineal remained the primary source of red dye until the 1850's when synthetic dyes began to be produced.
In the 1970's concern over the safety of synthetic red dyes used in food products led to a revival of the use of cochineal. Today cochineal extract, also referred to as carmine, is utilized as an organic food coloring in many products from fruit juices to ice creams and yogurt.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161. - Updated: June 27, 2004
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