"Last year we had 32 cases of logo abuse and 17 this year," said Steve Hodgson, general manager of the group that represents the UK’s building-preservation industry such as wood-preservation and flood-remediation as well as invasive weed control companies.
"As a well-established trade association it is natural many companies want to join us but some unscrupulous people try to do so without undergoing our strict criteria for membership.
"Some unauthorised contractors end up using our logo.
"It is important people are aware of logo abusers. If a member is not listed on our website they are not part of the association. If there is any doubt, they should contact us and we will confirm a company’s membership to them."
Registered weed-control members include Wise Knotweed Solutions in Scotland, Phlorum in East Sussex and Musketeers Group in London.
PCA members are able to carry out specialist surveys as part of house-buying procedures to identify potential problems.
PCA is a member of TrustMark, the Government-backed scheme that aims to help consumers find trustworthy tradesmen.
Hodgson said expert assessors audited every member to check quality of work on site and carried out technical, financial and operational verification visits.
The news follows a recent announcement by TrustMark that online searches by consumers for accredited landscape gardeners shot up nearly 50 per cent compared to last year.
Homeowners looking for landscapers on the TrustMark website notched up 57,000 viewings.
"With the economy in downturn many people do not have the money to move or overhaul their house or garden," said TrustMark spokesman Stuart Carter.
"But they may still need a professional, so consumers need to be extra vigilant and use reputable, legitimate people."