A Life-Sapping Threat

By NONA YATES

March 19, 1996 12 AM PT

TIMES STAFF WRITER

At first, the experts didn’t recognize the scourge that was killing off the usually hardy oleanders around Palm Springs.

They were concerned. Oleander’s colorful blossoms and toxic green foliage are ubiquitous in Southern California yards, along freeways and beside golf courses. If the dependable oleander was wiped out, a lot of people would be unhappy.

So a small army of horticulturists, entomologists and others began investigating what they decided to call “oleander scorch.”

It appeared as if the afflicted plants in the desert around Palm Springs were not getting enough water, or perhaps were suffering from salt burn caused by an overabundance of salt in the soil.

“Hundreds and hundreds of 30-year-old oleanders are dying” in the Coachella Valley, said Mike Henry, environmental horticulture advisor at the University of California Cooperative Extension office in Riverside County.

Although the symptoms mimicked those of salt burn or drought, the cause turned out to be something more serious.

A new strain of bacteria, possibly spread by a newly introduced insect, was attacking the desert oleanders, leaving brown stretches of dead and dying plants along the tony golf courses and multimillion-dollar estates of Rancho Mirage and other communities.

Officials believe that a new strain of Xylella fastidiosa, a bacterium that has been present in California for generations, is responsible.

It is apparently spread by the glassy-winged sharpshooter, a species of leafhopper insect native to the Southeastern United States and newly introduced to Southern California.

The emergence of this new bacterial pest has researchers, growers and agriculture officials worried.

“We’ve never seen such a disease in oleanders,” said Alex Purcell, a leading entomologist at UC Berkeley who has been working on the problem with researcher Barry Hill and others.

“We’re extremely concerned about it. It could be a very bad pest, one that we haven’t had before, more severe than other oleander pests,” said Jack Wick, regulatory consultant for the California Assn. of Nurserymen in Sacramento.

Wick pointed out that the oleander is subject to a number of plant diseases, but few, if any, will kill off the hardy plant.

Oleander is popular for its disease- and drought-resistant qualities. Its virtues as an ornamental landscape plant are many: It is easily and inexpensively grown, requires little maintenance and minimal pest control and provides privacy, safety and attractive blooms year after year.

Oleander is native to the warm climes of Asia and the Mediterranean, making it particularly suited to the deserts and valleys of Southern California. The plant has narrow dark green leaves that stay green year-round and large attractive red, pink or white flowers that bloom from about May to October.

All parts of the plant are poisonous if eaten. Officials go so far as to advise against using the wood in barbecues or as skewers. Even the smoke from oleander wood fires can be irritating, they say.

More than 60 people, representing such groups as Caltrans, the nursery industry and plant pathologists, met in Riverside recently to discuss this newly identified disease.

Caltrans officials estimate that e 2,100 miles of freeway in the state are landscaped with oleander, Henry said. To replace them all could cost $52 million.

A two-mile-long hedge at the Walter Annenberg estate in Rancho Mirage was one of the first places where oleander scorch was identified. Landscapers had to replace the once-immense and verdant privacy hedges with a wall.

Although the disease has been positively identified only in Riverside and Orange counties, the insects have been found in other areas, including Los Angeles and Ventura counties. Officials say it is likely that the disease will make its way to those areas as well.

“They have the insect that carries the disease in Los Angeles, but no reports of the disease. We don’t know why at this juncture, but it’s probably only a matter of time,” Henry said.

Agriculture officials believe the sharpshooter leafhopper carries the disease by feeding on an infected plant, sucking juices from it, moving on to a healthy plant and infecting it with the disease-causing bacterium.

“Sharpshooters are extreme animals; they have the highest feeding rate of any terrestrial animal, 100 to 1,000 times their weight in [plant] sap,” UC Berkeley’s Purcell said.

Feeding on only the sap, instead of the leaves or stem, also protects the insect from the otherwise poisonous effects of the oleander, Purcell added.

“The sap doesn’t contain the nasty compounds, so they’re usually unaffected by it,” he said.

Damage to oleanders is first evident with brown leaf tips, spreading to the branches and finally resulting in a brown, dead plant. The bacterium attacks the plant’s water-conducting system, effectively choking off its water supply.

When landscapers in the upscale communities of Palm Desert and Rancho Mirage first noticed oleanders starting to wither, they tried the standard treatments for salt burn and lack of water, then turned to scientists for help.

“This species [of bacteria] has been in California for well over a hundred years. It wiped out the grape industry in the late 1800s,” Henry said, referring to a similar outbreak that destroyed more than 35,000 acres of Southern California grapes. “This is a new strain, though.”

Other strains of the bacterium can cause disease in various plants, many of them highly valuable agricultural crops such as peaches, grapes and plums. Scientists don’t know enough about this new strain to know whether it will attack valuable agricultural crops, however.

“If we are ever to get a strain that causes disease in citrus, we could be in trouble,” Purcell said. “It doesn’t seem to affect citrus, but we may not be out of the woods yet.”

Henry said specialists are trying to determine if the newly discovered strain will infect other kinds of plants. So far the damage has been limited to the oleanders.

“It’s hard to say what other things it might get into, but at this point we know it’s different enough” from other strains, Henry said.

“This has a potential to be a major pest in California because there are so many oleanders here.”

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Imported Pests

About half a dozen new exotic pest species are introduced to California each year, many with potentially destructive consequences. Here are a few recent discoveries and their places of origin:

STRUCTURAL PESTS

* Indian House Cricket (Sri Lanka)

Colonizes houses and other structures. Scavenger, feeds

on leftover food, makes irritating noise.

* Asian Cockroach (Japan)

Possible health hazard. Will fly when disturbed. Found outdoors, active at night.

* Formosan Termite (China)

Extremely destructive structural pest. Can destroy a house in two years.

* Red Imported Fire Ant (Argentina)

Very aggressive, can inflict painful stings. Attracted to a variety of foods.

AGRICULTURAL PESTS

* Silverleaf Whitefly (Uncertain; first detected in Florida in 1985)