Our local daylily club introduced some new daylilies into the club garden earlier in the year. The new daylilies were from Florida and apparently were hosts to a rust disease. The disease is spreading and causing a mess. Once introduced into the garden, rust is expensive / difficult to control. I've been told that this disease could have been prevented if the plants had been properly treated before being added to the garden.
This experience got me to thinking. What other plant diseases are commonly introduced into the garden by bringing in plants from other areas? I recently traded for some wild species roses from someone in VA. Is there a danger of introducing disease into my garden with these plants that I wouldn't likely have to deal with otherwise? What types of plants are likely to present a danger if brought in from other areas and not properly treated/quarantined?