A dopey dealer thought he was peddling Spice to customers - but it was actually marshmallow leaves with WD-40 sprayed on them, a court heard.
Zachary Gaffey thought he was selling the drug , which was branded a "plague" by a judge.
But the court was told the leaves has been coated in the oil to give it 'the appearance and smell of Spice'.
The 27-year-old was jailed alongside Aidan Kay, 25, who helped him deal in return for drugs, at Manchester Crown Court.
They have also been in now indefinitely banned from visiting a number of areas in the city, the Manchester Evening News reports.
The court heard that Gaffey and Kay were seen by police at the Pagoda in the city's Chinatown in September last year.
"It's a matter of public knowledge that this area is frequented by a number of Spice users," Saul Brody, prosecuting, said.
Gaffey was seen with a JD Sports bag containing a 'large quantity of vegetable material'.
The court was told that Gaffey had bought it, believing it to be Spice, with the intention of selling it on to users.
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But it was later revealed that the material was not actually Spice, but marshmallow leaf sprayed with WD-40, 'which gives it the appearance and smell of Spice'.
"It would potentially deceive an impaired purchaser as to its quality," Mr Brody said.
Kay was said to be 'giving willing assistance', as they put some of the material into a smaller plastic bag to be sold on.
The pair were arrested, and Kay told officers: "I can take you to a tonne of Spice.
"The day before Gaffey was seen acting suspiciously, and when stopped on Market Street he was found to have a small amount of Spice in a bag he was carrying.
After being arrested, Gaffey said: "You are arresting me for having enough for a spliff in my bag."
Gaffey, who was previously jailed for more than five years for robbing a shop with an air pistol, later told the police he was a Spice user, and had been addicted since 2012.
Kay is from St Helens, and said he had been travelling to Manchester to buy Spice.
Defending, Michael James said that Gaffey, who also has previous convictions for possession with intent to supply heroin and crack cocaine, is 'easily led' and was dealing with others more sophisticated than himself.
Mr James said Gaffey became homeless, and was selling Spice to fund his own habit as well as to pay for his sustenance.
Ben Kaufman, defending Kay, said that his client had also been addicted to Spice for a number of years, after using it to try and stop using crack cocaine and heroin.
"The sad reality is it (Spice) is perhaps more readily available in custody than it is while one is at liberty," Mr Kaufman added.
Gaffey was jailed for 30 months, including 15 months for the drugs offences and a further 15 months after breaching two previous suspended sentences.
Kay was jailed for seven months, and is expected to be released soon because he has been on remand in custody since September last year.
Sentencing, Judge Timothy Smith said: "This case involves the supply of a drug known as Spice. That drug has caused mayhem in the city centre.
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"It has in particular affected the areas of Piccadilly Gardens and Chinatown.
"It has been described during the course of this hearing as a scourge on this city, an epidemic.
"Its impact on the local community cannot be overemphasised.
"It is quite simply a plague on this city."
Gaffey, of no fixed address, pleaded guilty to one count of attempting to supply Spice, and one count of possessing Spice.
Kay, of St Helens, pleaded guilty to one count of attempting to supply Spice.
Meanwhile, police in Manchester have recovered a massive haul of Spice worth £20,000 when they carried out a raid in the city.
One man has been arrested.
