Officials Abandon Spraying Deadline : Medflies: New outbreaks make control uncertain. At least one or two more helicopter attacks are planned, and applications could continue indefinitely.

Agriculture officials retreated Friday from a self-imposed May 9 deadline to wrap up most malathion spraying for the Mediterranean fruit fly over Southern California, admitting they had been overly optimistic in their projections of victory against the pest.

The officials said the reversal was prompted by a flurry of newly discovered outbreaks within the region and uncertainties about supplies of sterile Medflies, with which they had intended to replace pesticide spraying as their chief weapon in the 10-month-old campaign.

“We have experienced some difficulties,” said Isi Siddiqui, assistant director of state agriculture and the official in charge of the eradication effort. He described as “premature” the optimism that prompted the deadline to be established in March.

The announcement was made at a press conference in El Monte, where scientists who advise the state’s eradication effort had been convened this week to assess the feasibility of the tactical switch to “steriles,” which are used to breed wild Medflies out of existence.

While details were scarce, officials made clear that, for a broad swath of the region, the malathion helicopters will make at least one or two more of their noisy nighttime passes.

Moreover, any new infestations discovered through June probably will be attacked with a vigorous campaign of weekly spraying, a shift from the intended strategy of spraying one or two times and then releasing sterile flies.

All repeated malathion spraying will have to take place every seven to 10 days--more frequently than the semimonthly pattern followed through most of the infestation.

Officials said they will release a specific spray schedule next week.

The only sectors that officials said face certain continued spraying are Garden Grove in Orange County, Woodcrest in Riverside County and the city of San Bernardino.

For other sectors, constituting 400 to 470 square miles of spray zone, there are three main courses of action: Spray every seven to 10 days for an unspecified amount of time; stop spraying on schedule and release sterile Medflies, or phase out pesticides after one or two more applications. In a few neighborhoods, such as Sylmar, the pest is believed eradicated and they will not face treatment of any sort.

The five scientists who serve on the advisory panel also recommended several additional measures to ensure that the eradication strategy will be more aggressive in the coming months. For example, spraying will now start after a single fly is found. The previous criterion was two flies.

The panel also recommended enlarging spray treatment zones in an effort to stop the infestation just outside the zone. The scientists did not specify how much larger the treatment zone should be.

The slipping of the May deadline and the strategic alterations already have been approved in principle by state Department of Food and Agriculture Director Henry J. Voss.

It was Voss who, with public outcry over the pesticide applications mounting, pledged last March to end spraying in all infested neighborhoods by May 9 and to attempt to treat any subsequent infestations mainly with sterile flies.

Scientists advising the state opposed the deadline from the start, saying it was premature. In the past weeks, officials expressed increasing uncertainty over their ability to stick to the May 9 deadline. As recently as Wednesday, agriculture officials released a tentative schedule that showed that most spraying would end May 14. The schedule is now being revised.

Roy Cunningham, a U.S. Department of Agriculture entomologist who chairs the science panel, said he believes the pest can still be eradicated.

“We have not lost the war and we are not retreating,” Cunningham said.

Cunningham and other scientists, however, expect numerous new outbreaks this summer, when the weather warms and fly activity increases. If this occurs, he said, aerial spraying could be needed in the region “through the end of the calendar year and possibly into next spring.”

“I think it’s time for a stock-taking,” said panel member James Carey, a UC Davis entomologist. “It’s not clear to me that everything is under control. The moment of truth is July and August.”

The malathion assault now is designed to avoid major crop damage later.

Damage is caused largely when females deposit their eggs into fruits, vegetables and nut crops, causing them to rot, and making them unsalable.

As such, the Medfly represents a major threat to the state’s $1.5-billion fruit crop. In 1981, a Medfly infestation led to the loss of $100 million to California growers and resulted in international quarantines.

But the announcement of more spraying revived criticism of the state effort.

“They’re going to continue spraying here?” said Huntington Beach City Councilman Peter M. Green, a biology professor at Golden West College and an ardent malathion critic. “That’s insane. They’re finding fruit flies in areas that they’ve sprayed eight to 10 times, and that to me says this stuff is not effective.”

Assemblyman Richard Katz (D-Sylmar), who has been one of the most outspoken critics of malathion spraying, said: “What this indicates is these folks have no clue what they are doing.”

The five members of the Medfly Science Advisory Panel were unusually quiet about the strategic switch. Several members of the science panel said they have been instructed not to comment on their discussions during the week or some of the more controversial aspects of the issue.

The state has spent the last few weeks warily watching as new discoveries were made in several previously uninfested localities, and also a couple of neighborhoods that had been repeatedly sprayed. At the same time, officials were scrambling to assess their supply of sterile flies and how best to distribute them.

The sterile flies are to come mainly from three breeding facilities in Hawaii, among them a new plant with the capacity to produce 500 million sterile flies a week. So far, this federal facility only has been able to raise about 40 million sterile flies a week.

If potent medflies mate with sterile flies their eggs will never hatch, thus ending the infestation.

The new strategy unveiled Friday is essentially a return to the recommendations that the science advisory panel made in March but were overruled by Voss.

At that time, no new Medflies had been found for five weeks, leading agriculture officials to express cautious optimism that the battle was being won.

Voss believed an abundant supply of sterile flies would arrive in California on time--enough to even have a reserve to treat any new infestations.

The science advisory panel believed that Voss and his staff were being overly confident.

The announcement to end spraying in May was partly political, coming amid increasingly vocal objections by residents and local dignitaries about the mass pesticide program.

The scientists noted that under Voss’ timetable spraying in certain neighborhoods would be aborted just one or two applications before completion of the original spraying schedule. They argued that it would be better to finish the spraying and ensure eradication.

This, they said, was needlessly courting danger.

“I can’t understand why they decided to paint themselves into a corner,” Cunningham said at the time. “Seems like they shot themselves in the foot on this one.”

Just one day after Voss’ decision, the plan began to unravel--a new Medfly was discovered in the city of Diamond Bar. The single fly proved to be the first of a rash of discoveries from Hancock Park in Los Angeles to the agricultural community of Woodcrest, more than 60 miles away.

Times staff writers Eric Lichtblau and Richard Simon contributed to this story.