ALBA, Italy—Kira trotted into the misty forest, sniffing forensically around the oaks and poplars where hounds have long hunted for the precious white truffles for which this part of northern Italy is famed.

But Kira, a police dog, was hunting for poison.

Truffle hunters are trying to poison one another’s dogs with tainted snacks hidden in these rolling, wooded hills. Italy’s Carabinieri police are trying to crack down on the canine killings.

Kira’s job is to protect some of the world’s best truffle-sniffers from munching on suspect morsels. “She has to find poisoned bait before other dogs do,” said Kira’s handler, Agent Emanuele Gallo, trudging through the muddy undergrowth behind the 11-year-old Belgian Malinois.

Locals blame turf wars in the secretive truffle community. A lump of the buried fungus can be worth hundreds of dollars. Sometimes, dogs are paying the price.

Saverio Dogliani’s dog Floki was poisoned early this year for the second time. Someone had hidden meatballs laced with snail bait on woodland owned by Mr. Dogliani. Floki, a 3-year-old Brittany whose highly honed snout can sniff out truffles buried many inches beneath mud and leaves, narrowly survived both times.

Saverio Dogliani, a truffle hunter, said his dog narrowly survived two poisonings.

“It’s all about getting rid of the competition,” said Mr. Dogliani, a 57-year-old who has been a truffle hunter, or trifolau in the dialect of Italy’s Piedmont region, since he was a teenager.

These days, Floki wears a muzzle to stop him from eating dangerous morsels, although it makes hunting harder.

The hills around Alba, a Piedmontese town renowned for fine red wines, also hide the world’s most expensive truffles. The prized white fungi, more sought-after than common black truffles, mature in the autumn, stay fresh only for a few days and draw buyers from all over the world.

Prices for Alba white truffles reached a record high of around $800 for 100 grams, around 3.5 ounces, at the town’s truffle fair this fall. A few shavings of the raw, bulbous delicacy can more than double the price of a dish in a fine restaurant—and that is in Alba. The fungi fetch more the farther they must travel. Chefs say it is all worth it for the earthy, pungent aroma.

Prices for Alba white truffles reached a record high at the town’s truffle fair this year.

A few truffle shavings can more than double the price of a dish in a fine restaurant.

“There’s nothing in the world like it,” said Giorgio Pignagnoli, a Michelin-starred chef cooking for guests at the Alba fair, after topping dishes of quail, foie gras and licorice with truffle shavings.

The luxury ingredient is getting more expensive because of strong global demand—but also shrinking supply. The steadily warmer, drier climate in Piedmont means fewer truffles. This year, the forests yielded one of most meager bounties that trifolau and traders can recall.

That is intensifying the rivalry among truffle diggers.

“It’s getting worse,” said Agent Gallo. “There is more competition, and unfortunately illicit means are being used more.”

It takes special dogs to find truffles. They are often water dogs or spaniels and their training starts early, sometimes by dipping their mother’s teats in truffle oil. A puppy from good truffle-hunting stock can cost around $1,000. Fully trained, talented pooches are hardly ever traded.

The trifolau go to great lengths to hide where they hunt. They park their cars miles away. Careful not to leave tracks, many avoid hunting in snow.

“The footprints would be too easy to follow,” said Roberto Bonetti, who was selling his truffles at the Alba fair.

Some won’t talk about their hunting habits at all. “I can’t speak. My teeth hurt. I have a sore throat,” said Bruno Gallo, an 82-year-old trifolau.

Many hunt in the dead of night, even if that means venturing into the forest when wolves and wild boars prowl. “We carry torches with us, which we rarely turn on,” said veteran truffle hunter Ezio Costa.

Veteran truffle hunter Ezio Costa said there is a lot of competition.

As dusk settled over a damp woodland, Mr. Costa’s dog Dora rummaged through moldering leaves and tangled roots before a familiar scent filled her nostrils. She began digging. Her owner finished the job with a small hoe, carefully unveiling an apricot-sized truffle.

Mr. Costa stashed the truffle in his pocket and meticulously refilled the hole with soil, covering it with dead leaves.

“Covering it up very, very, very well is the most important thing,” Mr. Costa said. The fungus leaves spores behind, and another might grow in the same spot next year. “There’s competition. A lot of competition.”

The contest has always been fierce. Dog poisonings have been known for decades. Some locals say it is rare these days. “Here we’re all well-behaved,” said Mr. Costa.

Not so, says Carabinieri Col. Nadia Bessone, who is investigating dog poisonings near Alba. “It’s very common in this environment,” she said. “They are targeting their economic rivals.”

The poisonings finally drew the attention of law enforcement two years ago. This fall, the forestry police deployed its team of toxin-detecting dogs to inspect swaths of the truffle-rich forests, in a show of force to dissuade potential poisoners.

But solving the crimes is hard in the tight-lipped truffle community.

Emanuele Gallo said his dog, Kira, has to find poisoned bait before other dogs do.

“Cases are rarely reported. There is a degree of omertà,” said Col. Bessone, referring to the code of silence usually associated with the mafia. Only three official complaints of poisoning have been reported to her team. “But there are many more,” she said.

One veterinarian in Alba said he treats eight to 10 poisoned truffle dogs a year. The chances of survival depend on the type of poison. Dogs that eat snail bait, the most commonly used poison, can be saved if they are immediately rushed to the vet.

The poisonings are sometimes punishment for straying onto another trifolau’s turf, a concept governed by unwritten rules. Sometimes, a hunter in a contested area receives a warning, such as slashed tires, or ground beef stuffed into a car’s handle.

Finding proof is hard, because snail and rat poisons are legal and common. “If I find some ground beef in someone’s fridge, that’s not evidence,” said Col. Bessone. “It’s not like someone would keep a stack of poisoned meatballs ready for use.”

On a recent morning in the woods, Mr. Dogliani, the trifolau, told Col. Bessone he had overheard chatter in a local cafe: Two more dogs had been poisoned a half-hour’s drive away. The rumor hadn’t reached the police.

Martina Aloi remembers the day, four years ago, when she took a newly engaged couple from New York on a truffle hunt in her family’s private forest. “It was supposed to be a romantic thing,” recalls the 24-year-old.

Martina Aloi and her new dog check a spot for a truffle in the woods near Monta, Italy.

Ms. Aloi with her truffle-hunting dog Tea, who died four years ago after being poisoned.

Her truffle-hunting puppy Tea fell ill after munching on something in the forest. It turned out to be chicken laced with herbicide. By the time they reached the vet, it was too late.

In her village, Ms. Aloi says she was pressed to hush up the killing. “They didn’t want me to report the poisoning. They said it would look bad,” recalled Ms. Aloi.

She ignored the advice and went to the police, who temporarily halted truffle hunts in the area and inspected the woods. They could never prove who did it. “We have our suspicions,” says Ms. Aloi.

On a recent search for truffles, Ms. Aloi watched carefully over her new dog, Mia. “Hey sweetie, what are you eating?” she called.

Mia foraged on up a steep, slippery hill. She began burrowing with her snout near some poplars. Ms. Aloi dug up a muddy nugget of Alba’s white gold, and fed Mia a treat.

Emanuele Gallo and his dog search the woods in Narzole, Italy.

Write to Margherita Stancati at margherita.stancati@wsj.com