UK growers are banned from importing ash, platanus and sweet chestnuts into the UK, but landscaoe contractors, landscape architects, garden designers and the public can still import direct.
Speaking at FERA's 'Plants Need Passports Too' Chelsea Flower Show exhibit, Paterson said: "I've made protecting the country from plant diseases a top priority for the first time ever."
He said Defra has applied Gilligan task force recommendations "very rapidly" including appointing Spence, drawing up a risk register, publishing a plant health strategy and working on a new biosecurity strategy as well as having new monthly biosecurity meetings to assess animal and plant risks.
Paterson said the loophole that allows internet sales of banned trees "is a backlog from the past".
He added: "I'm aware the current regime massively needs improving. I've been to Australia, and New Zealand and seen how much more seriously they take it."
"Within the constraints of European free trade we're quite clear that we want to make our borders as secure as possible. We do have the advantage of being an island.
"Emphatically we will look at all areas where we can to try and protect the country from the import of plant diseases. It is something Nicola will be looking at as part of our whole strategy.
"The point of this stand is to get the message across to the public that they too can help."
Chief plant health officer Nicola Spence said: "The potential is there particulary in internet trade, there's a pathway for material coming in that is not registered because we're not aware of it. It's important we look at this with the trade bodies."