Exotic-Pest Primer
The following is a sampling of exotic, invasive pests found in Southern California gardens:
* Ash whitefly: This insect, which attacks fruit and shade trees, was first found in California in the late 1980s and quickly built up populations, causing defoliation, loss of fruit and in some cases, tree death.
It had a severe impact on the shade and fruit tree industry and commercial pomegranate orchards. Fortunately, this pest has been brought under control by a parasitic wasp introduced from the ash whitefly’s native habitat of the Middle East and Mediterranean, and it is no longer a threat.
* Black scale: This has been a periodic citrus pest in Southern California and a consistent problem for olives in the San Jacinto Valley. It is thought to be a native of Africa that entered California before 1880. It now infests a wide variety of plants.
Until a natural enemy was introduced from South Africa in 1940, it was a severe pest. Unfortunately, this natural enemy does not suppress the scale on a consistent basis, so it remains a problem, infecting leaves, branches and, at high levels, decreasing fruit size and production.
* Eucalyptus longhorned borer: This borer, which was discovered in Orange County in 1984, is one of several pests that attack and kill eucalyptus trees. It causes a lot of destruction in its larval stage when it feeds on the tree’s tissue, cutting off the nutrient supply. Once an infestation is discovered, it is often too late to save the tree.
Removal of dead trees costs from $500 to $5,000, depending on size and location. Researchers are trying to control this pest by educating homeowners and landscapers on keeping trees healthy. They are also conducting studies on resistant eucalyptus species and establishing three species of parasites that attack borers.
* Formosan subterranean termite: This highly destructive termite commonly makes infested homes in Hawaii uninhabitable within two years. One colony can contain more than 1 million termites. Introduced more than 10 years ago from Hawaii, it has a strong foothold in San Diego. It is native to mainland China.
There are no consistently good controls for this insect. Researchers have done some baiting with an insect growth regulator that has shown some promise in a limited area.
* Giant whitefly: Scientists believe this destructive pest is native to Mexico. Thought to be one of the most serious landscape pests in California, it attacks more than 50 common ornamental plants, seriously damaging them by feeding on sap, which leads to defoliation, stunting and possible plant death.
Giant whiteflies reproduce rapidly and have been found in Texas, Louisiana and Florida. Several whitefly enemies, which are miniature wasps, have been discovered.
Researchers are evaluating the wasps in field trials in California, which include areas of Orange County. These natural predators show some promise, but the final results are not yet in.
* Mediterranean fruit fly: This infamous fruit fly was first found in Southern California in 1975 and as recently as 1998.
The medfly affects a huge range of plants, attacking at least 253 species of fruits, nuts and vegetables. The female flies deposit eggs underneath the skin of fruit, which produce maggots that make the fruit rot.
Researchers are studying the medfly’s behavior in Mediterranean countries for ideas on control and eradication.
* Red gum lerp psyllid: New on the scene is this Australian native, which has caused major damage to eucalyptus trees from Sacramento to San Diego. Originally detected in 1998 outside of the Agricultural Commissioner’s office in South El Monte, it spread throughout the state almost overnight.
This insect feeds on plant fluids, causing eucalyptus to lose their leaves, and can kill a tree if left untreated.
A researcher from UC Berkeley brought over six Australian parasites that are natural enemies of the psyllid. These will be evaluated over time for possible release.
In the meantime, researchers suggest creating conditions that are unfavorable to the psyllid, which include keeping eucalyptus well watered, but not overly wet. Also, don’t over-fertilize or overprune.
* Red imported fire ant: This dangerous South American insect is a major problem in the southern United States. The sting of this ant is painful and causes a pustule on the skin that can scar if infected. In rare cases, the sting is deadly.
In Texas, where it is firmly entrenched, more than $1.1 billion is spent annually on fire ant pesticides. They were detected in Orange County in 1998. Researchers are examining the behavior of these insects, especially in relationship to water (they’re attracted to irrigated areas) for clues to controlling their spread. Several insecticides are also being studied.
