The top 15 garden diseases The RHS has analysed the enquiries it receives from gardeners last year to create a list of the most troublesome garden diseases in 2012. Here they are. Honey fungus Honey fungus, the most destructive fungal disease in British gardens, topped the list just as it did in 2011. The fungus spreads underground, attacking the roots of perennial plants, and cannot be controlled by chemicals. Picture: H