Benn's visit took him to Newlyn Fish Market, National Trust Trengwainton Gardens, Winchester Growers, the Eden Project and the Tregothnan Estate, to visit its tea plantation and see manuka honey production - the first outside New Zealand.
He said: "It's partly a fact-finding visit. The horticulture industry is important and it is a much bigger market than it was 10, 20 or 30 years ago."
About Phytophthora, he commented: "It's a concern and we have put in a very considerable amount of money through Defra, via the research programme.
"The National Trust has been doing terrific work. And as we walked round the garden I heard they are trying to understand the nature and extent of the disease.
"So it's about getting the science as good as possible, providing information and advice - including testing kits to enable people to find out which type it is.
"And then it's about making the choice about whether or not you take the plant out.
"But in the end you may have to make some difficult choices to protect the things that are most valuable."