By Vicky Boyd
The San Joaquin County Agriculture Commissioner’s office trapped two Oriental fruit flies near Tracy in mid-October, setting in motion concentrated surveying and localized treatment programs. The California Department of Food and Agriculture won’t impose a more restrictive quarantine unless six or more flies are found.
But the discovery nonetheless raises concern among growers of the more than 230 crops the invasive pest can attack and damage. “It’s kind of frustrating that something like this comes up,” said Jake Samuel, who grows walnuts and cherries with his dad and brothers near Linden. “The last thing we need is another fruit fly.”
He remembers having to go through a pre-harvest treatment protocol the last time an invasive fruit fly was found in the county in 2012 or 2013. “It was quite extensive,” said Samuel, also San Joaquin Farm Bureau second vice president. “That’s what the concern is. It’s just one extra thing we have to make for the cherries that adds to the cost, and it’s another trip through the field.”
Among the Oriental Fruit Fly’s extensive host range are apples, bell pepper, cherries, citrus, grapes, figs, pears, persimmon, pomegranates, stone fruit, tomatoes and walnuts. Females lay eggs on the host fruit just under the skin’s surface. When they hatch, the maggots feed on the flesh, rendering the item unmarketable.
Don’t pack a pest
San Joaquin County Ag Commissioner Tim Pelican said he didn’t know where these particular flies came from. But he said inspectors using trained dogs regularly intercept Oriental fruit flies as well as other serious pests in parcels coming through the Sacramento postal distribution center. San Joaquin County ag inspectors visit FexEx and UPS nearly daily to conduct similar inspections of incoming parcels, and they’ve found invasive pests in the past.
“I think we want people to understand to not bring or have people send them fruit from outside of this area, because that’s generally how these pests are spread,” Pelican said.
The first Oriental fruit fly, a male, was trapped Oct. 14 in a residential part of Tracy as part of a regular pest detection program conducted by the ag commissioner’s office. For fruit flies alone, the office deployed 2,100 traps within the county this season.
In response to the first fly, CDFA crews began a delimiting survey in an 81-square-mile area around the trap catch. It involves hanging additional traps, concentrating within a 1-mile radius of the first catch. The second fly, also a male, was trapped a few blocks away, Oct. 16, near a residential persimmon tree during the delimiting survey.
The 81-square-mile survey area involves almost all of the city of Tracy as well as adjoining unincorporated portions to the south, north, east and west, Pelican said.
Most of the area to the west encompasses the foothills, which don’t have any host crops. Fortunately, he said, most of the host crops had already been harvested within other parts of the survey area.
Pelican also plans to contact Chris Zanobini, executive director of the California Cherry Board, about pre-harvest quarantine treatment protocols for the 2020 cherry season.
Because the delimiting survey will go into early next summer, cherry producers within the 81-square-mile area may want to consider the four-application quarantine pre-harvest treatment. That way if flies are trapped during harvest, shipments of their fruit won’t be held up, he said
CDFA takes the lead
CDFA has taken the lead in the trapping and treatment effort because San Joaquin County’s seasonal trapping program ended Oct. 31. “It gets difficult for us to take on this long of a period because our seasonal people we use for trapping can only work so many hours,” Pelican said. “Normal trapping season ends in October and for some reason, that’s when you typically find flies is in late September and into October. “This does show that when you have a seasonal group that comes back year after year, they know what they’re looking for.” This year, 34 technicians were involved with seasonal trapping.
CDFA crews also have begun what’s known as male attractant treatments within the 1-mile core area. They involve squirting quarter-size dollops of a male attractant on telephone poles or other permanent structures about 8 feet from the ground. The dollops also contain a minute amount of Spinosad, an organic insecticide, which kills the male flies once they feed on the attractant. The treatment is specific to this fly family and is harmless to other insects, including beneficials. The technique has worked successfully in countless other fruit fly infestations in recent years.
If no more flies are trapped, the area will have to go through three generations until the pest can be declared eradicated. Depending on weather, which affects the speed of fly development, that could extend into late June or early July 2020, Pelican said.