Were the terrorists who torched 14 tractor-trailer rigs at Harris Farms in California’s Central Valley unaware that the drivers of those vehicles sometimes slept overnight in those rigs?

Or was surveillance by those terrorists so pronounced that they knew nobody was in those rigs in the early morning hours as they set fire to them on Jan 8, 2012.

Either scenario is chilling to Tom Knowles, a retired agent with the Federal Bureau of Investigation and a terrorism authority with the Sacramento Regional Terrorism Threat Assessment Center.

Knowles was among three speakers at an ag crimes and terrorism summit who warned that the central San Joaquin Valley, boasting billions of dollars in agricultural production, can be vulnerable to attack from terrorists from abroad or homegrown.

Their observations came at the Kearney Ag Center in Parlier at an event presented by the University of California Cooperative Extension, Fresno County Farm Bureau, Fresno County Sheriff’s Office and the Fresno County Department of Agriculture.

A Kingsburg native, Knowles said he has been involved in investigations of all terrorist bombing attacks against the United States since the first Trade Center bombing in 1993, with the exception of the bombing of the federal courthouse in Oklahoma City.

Both Knowles and Fresno County Sheriff Margaret Mims conceded that investigation of terrorist actions is complicated. “They require marathon investigations,” Knowles said. But he believes if suspicious activity on Valley farms is reported, those responsible can “easily be caught.”

There have been no arrests in connection with the Harris Ranch arson that caused more than $2 million in damage.

Both Knowles and Mims showed a message posted on the Web by the North American Animal Liberation Front. It closed with the jarring phrase: “Until next time . . .”

“It leaves no doubt they’re coming back,” Knowles said. “It’s game on time.”

He believes a key to stopping such actions — and perhaps finding those who did the damage at Harris Farms — lies in heightened awareness among growers and field workers and paying more attention to what could be suspicious activity.

(For more on agroterrorism awareness and prevention, see: US agriculture waking up to agroterrorism threat)

Knowles, who is with the Sacramento Regional Terrorism Threat Assessment Center, said agriculture is particularly vulnerable to attack because “you don’t have to touch it to cause problems.” It can be enough to simply feed into a perception that food is contaminated.

Knowles cited the example of a food safety scare in 1996 that cost California’s strawberry industry $11 million dollars, despite the fact that the parasite that was making some ill was subsequently traced to raspberries from Guatemala.

Likewise, cherry tomatoes were the casualty in more recent years of a food safety scare triggered by peppers from Mexico.

Al Qaeda

Knowles said that U.S. forces have found documents at an Al Qaeda training camp that showed interest in targeting farms in the United States, purposely contaminating food supplies by spreading contaminants that include foot and mouth diseases and hog cholera.

In 1986, a group calling itself the “Breeders” said it had released Mediterranean fruit flies in Southern California to protest aerial spraying of the pesticide malathion, said Carl Hafner, Fresno County agriculture commissioner. They also threatened to release the flies in the San Joaquin Valley, but apparently did not do so.

Hafner said there was evidence that the claim was not a hoax, including the discovery of unexpected life stages of the insect. The case remains unsolved.

Insects have been used as weapons in combat for decades, Hafner said, from warriors hurling hornet and wasp nests to combatants using stinging or biting insects for torture, spreading plague in infected fleas or yellow fever in infected mosquitoes.

Some of the material that Hafner presented came from a book called “Six-Legged Soldiers: Using Insects as Weapons of War” by Jeffrey A. Lockwood.

It’s well known that economic blows to agriculture can be struck by maliciously introduced insect vectors, pests that can carry viruses and bacteria throughout a crop.

Hafner said allegations of wartime use of insects for crop destruction arose during the Civil War and World War II.

As an example of the economic impacts of farm pests, Hafner cited the European grape vine moth. In March, a Fresno County quarantine triggered by the find of 11 moths was lifted, but it left producers with a cost of $11 million in treatment and compliance, Hafner said.

Hafner said the spread of pests “can open pathways for agricultural terrorists to disperse bioagents,”

She said customs and border checks help keep pests out of the fields and orchards of California, but cutbacks in funding have taken a toll. She cited the example of the loss of $84,000 in funding for inspections of beehives brought into Fresno County for pollination of almonds and other crops. Those inspections have been a key to keeping hitchhiking red imported fire ants out of the state.

Marijuana trafficking

Mims said her department is working with Cal Fire and the FBI on solving the Harris arson case, and she also used the symposium to warn growers about the growing of marijuana on farmland on the Valley floor.

“We will prosecute and your property can be seized,” she said.

Mims said trafficking in marijuana has been boosted by what she called “convoluted state medical marijuana laws.”

“It’s not about medicine, it’s about the money,” she said, pointing out that a single acre of marijuana can result in sales valued at $19 million.

Mims said the largest “marijuana grow” her department has hit was a 54-acre field outside of Sanger where plants were 12 to 13 feet tall.

She said her deputies have traced movement of marijuana to states well outside of California — “Texas, Arkansas, Tennessee, Utah, Massachusetts.”

The Valley pot business also poses physical threats to the innocent, Mims said, showing slides of a gun turret overlooking one growing area in Fresno County and a booby-trap placed in another in Kern County, using some fish line, a rat trap and a shotgun shell.

(For more on California marijuana farming, see: California’s growing marijuana business impacting agriculture)