Even by the permissive standards of partisan talk radio, the grave warning from the host of a program on a popular Spanish-language station in Miami one afternoon in September was outlandish.

Carinés A. Moncada, the host, claimed that a co-founder of Black Lives Matter practiced “brujería” - witchcraft.

“So you ask yourself, ‘Why are they destructive?’” she said, referring to protesters who support the Black Lives Matter movement. “Because they are vibrating with the devil. They are vibrating with negativity. They are vibrating with the dark.”

“And whoever votes for Biden, unfortunately, is supporting that,” she concluded.

Ms. Moncada appeared to be citing News Punch, a website known to publish conspiracy theories. She posted a link to a story the site published about witchcraft on Twitter. It was based on an interview in which the Black Lives Matter co-founder mentioned invoking the “spirits” of people who have died.

By repeating the racist tropes on the radio, Ms. Moncada spread it beyond her 45,000 Twitter followers and into South Florida’s mainstream broadcast media, a worrying circle of misinformation targeting Latino voters in the nation’s biggest presidential battleground state.

Some of the wild and baseless claims question the validity of the coronavirus death toll, and question whether Joseph R. Biden Jr. can be president because of his Catholic faith.

But some of the most insidious messages disseminated to Spanish speakers across the country, like the one shared by Ms. Moncada, are intended to pit Latino and Black voters against one another by using racist language - sometimes veiled, sometimes not - to cast those who protest police violence as untrustworthy and dangerous. The efforts aim to draw clear distinctions between Black and Latino voters, though Afro-Latinos make up a sizable part of the population.

Researchers say that the scale and extreme nature of misinformation, after ramping up in every election cycle for the past several years, have spiked this year.

“They feed into real fears, about the pandemic, about socialism and exploiting potential gaps within communities, between the Black community and the Latino community,” said Jacobo Licona, who studies misinformation for Equis Labs, a liberal-leaning Latino research group. “There’s misinformation from people not even understanding how they are spreading it, that continues to stoke real tension and anxiety right now.”

It is difficult, if not impossible, to know how much of an impact the false information is having on voters so far. Some Democratic strategists privately noted that internal polling was not showing that the rumors were effective in flipping would-be supporters of Mr. Biden toward voting for President Trump.

But experts say that much of the disinformation is designed to suppress support for Mr. Biden and is likely to increase in the final weeks of the campaign. If people are bamboozled, or take a pox-on-both-their-houses attitude, they may not bother to vote at all. Many researchers believe that disinformation, particularly in the final days of the campaign, most likely contributed to lower turnout among Black voters during the 2016 election.

And it remains, for now, impossible to know whether the misinformation is coming from foreign influencers and to what extent the distribution of misinformation is coordinated.

But the outright disinformation — the deliberate spreading of falsehoods — is coming almost exclusively from conservatives, researchers say, including from a crop of right-wing Spanish-language websites that are designed to look like nonpartisan news outlets. Liberal activists and experts have struggled to keep up with an accurate response, in part because of language barriers and because so much has been spread in private, closed groups.

Last month, the media nonprofit Poynter Institute announced a collective that included the Telemundo and Univision networks to combat misinformation on the messaging platform WhatsApp. A spokesman for WhatsApp said in an email that the platform has taken other steps to “help address the challenge of misinformation — to limit abuse and empower users,” including creating new limits on forwarding messages, in order to combat the spread of rumors.

Experts say that while YouTube took steps last week to remove content tied to the QAnon conspiracy theory, much of it remains in Spanish-language videos on the site.

And the private messaging has already seeped out to the public in Florida.

A vote for Mr. Biden, Ms. Moncada said on Actualidad Radio, Miami’s most popular AM radio station, according to Nielsen, with a niche among Venezuelan-Americans, means supporting anarchy and violence. “That is what you are voting for,” she warned.

Ms. Moncada did not respond to multiple requests for comment.

“This matter was handled internally and there are no further comments,” Adib Edén, the president of Actualidad Media Group, said in an email, without elaborating on what internal action was taken.

Many experts fear that the conspiracy theories are more dangerous amid the coronavirus pandemic, when people are searching online for information to keep themselves safe.

On YouTube, for example, a viewer watching horoscope videos can quickly be led to see content on supposed homeopathic medical remedies, which can then morph to conspiracy theories calling the response to the coronavirus overblown.

It is something akin to a slip-and-slide of falsehoods.

Misinformation proliferates first online, then is often shared on WhatsApp, which is particularly popular among Latino immigrants. Then, in Florida, it trickles into the Miami media market’s largely unchecked ecosystem of niche Spanish-language newspapers and radio and television stations, whose right-wing hosts and commentators amplify some of the pernicious messages.

Though this is most problematic in Florida, there is evidence of it spreading throughout the country.

Caroline Zepeda, a 30-year-old retail clerk in suburban Phoenix, chiming in on family text chains to offer legitimate facts about the spread of Covid-19 and proper precautions. But sometimes she is dismissed almost immediately.

“It’s painful and scary to see people you love and think should know better fall into these traps,” she said. “I do what I can: I talk to my mother and think I convince her, but it’s like every time I put one rumor out, there’s another one the next week or even the next day.”

WhatsApp, which uses encrypted messages between groups of fewer than 250 people, is notoriously difficult to track. And because messages are typically shared among people who know one another, the information is often presumed to be fair and accurate.

WhatsApp is exceedingly popular among Latinos with families living both in the United States and Latin America, and experts have seen what they call a relentless deluge of false information being passed from those living outside the United States about American politics - and then back again. Many people are reluctant to leave groups they have long been a part of to join in friendly family gossip and nostalgia.

“In the U.S., there’s not a huge WhatsApp penetration, but in certain diaspora communities, there is,” said Jacob Gursky, a research associate at the Center for Media Engagement at the University of Texas at Austin, which has studied disinformation in the United States, Brazil, India and Mexico and has been looking into the messages proliferating in Miami.

South Florida is home to robust diasporas from Venezuela, which has an abundance of sophisticated propaganda on social media, and from Colombia, where deep ties to the U.S. government have prompted Colombian politicians from both the right and the left to be increasingly vocal about supporting Mr. Trump or Mr. Biden. Senator María Fernanda Cabal endorsed Mr. Trump; Senator Gustavo Petro said that if he were an American, he would vote for Mr. Biden. Mr. Trump responded on Twitter by calling Mr. Petro a “major LOSER.”

Evelyn Pérez-Verdía, a Democratic Latino issues strategist in Weston, Fla., first noticed the proliferation of political misinformation in a WhatsApp group for about 200 Colombian-Americans in 2018. When she pushed back, the group’s administrator chided her, Ms. Pérez-Verdía said: “He said, ‘Evelyn, you are going outside of the purpose of this chat, which is about Colombians.’”

Ms. Pérez-Verdía said she had a similar experience this year when she objected to someone in another group purportedly about coronavirus information saying that true Catholics cannot be Democrats. She also said she had received videos claiming that Black Lives Matter planned an assault on the White House and that opposing Mr. Trump amounts to supporting the likes of Cuba, the Islamic State and Hezbollah, the “filth of the planet.”

“They’re using these chats to lie,” Ms. Pérez-Verdía said. “It’s a massive disinformation campaign. They’re definitely using these crazy tactics that they’ve also used in Latin America.”

One example of how conspiracy theories have invaded the mainstream came last month when El Nuevo Herald, The Miami Herald’s sister publication in Spanish, admitted that it published a supplement with racist, anti-Semitic, misogynistic and homophobic commentary for more than eight months.

In August, Radio Caracol, a Colombian network based in Miami, aired a paid program from a businessman who spewed racist and anti-Semitic claims about how a Biden win would lead to a dictatorship led by “Jews and Blacks.” The network quickly apologized, barred the commentator and allotted time on a popular afternoon program to discuss what went wrong.

Last month, Representatives Joaquin Castro of Texas and Debbie Mucarsel-Powell of Florida, both Democrats, asked the F.B.I. to investigate disinformation targeting Latinos in South Florida, citing the Herald and Caracol incidents and a Politico report on some of the most vile videos circulating on WhatsApp. A second letter sent on Oct. 7 noted that they had not received a response and asked for a briefing by Oct. 14.

They said they had received no response.

Randy Pestana, the director of education and training on cybersecurity at Florida International University, said the aim of recent disinformation campaigns had been to create zero-sum relationships to blur reality so that in the voter’s mind, “you’re either for the police, or you’re for Black Lives Matter.”

Much of the misinformation has come from the Trump campaign itself. Social media accounts for Equipo Trump and Latinos for Trump, official campaign operations, have claimed that Latin American socialists are promoting Biden and connected protests to actions in Latin American socialists countries, and that Democrats in the United States are responsible for them. Others have claimed that Democrats are ignoring attacks on Hispanic men.

“I didn’t see this in 2016,” Mr. Pestana said.

On Actualidad Radio in Miami, Ms. Moncada’s Black Lives Matter rant prompted a backlash, including from Christian Ulvert, a prominent local Democratic political consultant who also advises the Biden campaign. He yanked ads for some of his local candidates from the station.

About a week later, Ms. Moncada dedicated part of the program to thanking listeners for keeping it atop the local ratings.