Mr Cull made the comment after the Ministry of Business, Innovation and Employment (MBIE) said it was disappointed with what it found after inspecting six Castle St student flats as part of a crackdown on rental homes across the country.
Mr Cull, who owns student flats, said he fully supported the MBIE crackdown and called on the landlords caught out to lift their game.
``The landlords they have picked up in North Dunedin, frankly, are letting the city down.
``It's very easy for us to get a reputation for being a slum city if we have landlords that won't live up to their obligations,'' he said.
He supported the new rules, which required landlords to provide information to tenants about how insulated their properties were, and the introduction, from July 2019, of a requirement for all rental properties to be insulated.
He had long supported minimum standards for rental housing.
``As I've said in the past, it's against the law to sell food that makes people sick. I don't see why it should be legal to rent accommodation that makes people sick.''
He also stressed the importance of enforcement actions such as MBIE's visit to Castle St.
``I hope that MBIE extend its attention to other areas of town, like South Dunedin, where we know that some of the rental housing is not up to scratch.''
MBIE said the Castle St properties were inspected to determine whether landlords had been complying with the new law requiring them to state how much insulation a rental house had on tenancy agreements, introduced from July 1.
But MBIE said, surprisingly, there were still landlords who had not complied more than three months later.
MBIE investigations manager Paul Coggan said his team was ``disappointed'' with what it saw in Dunedin.
Otago Property Investors Association immediate past-president Wendy Bowman said good landlords had nothing to fear from the new legislation.
Most landlords would not have a problem with the new laws and had already insulated their properties, Ms Bowman said.
``Most landlords are socially conscious and want the best for their tenants,'' she said.
The requirement to provide information about insulation would probably reward good landlords, as tenants could be less likely to rent houses which had not been insulated.
