Rosa is a genus of woody perennials which includes dozens of species and thousands of cultivars of roses. Roses are grown all over the world and offer a extensive range of flower type, color, growth habit, and fragrance. The rose is the most popular flower in today’s gardens and one of the most economically important ornamental plants in North America. Despite their popularity, roses are hosts to many diseases and insects. Proper site selection and cultural practices, together with use of resistant cultivars will help reduce problems. Rose breeding work in North America has lead to releases of better adapted roses for landscape use. However, most cultivars are susceptible to foliage diseases, especially black spot, but also powdery mildew, Cercospora leaf spot, and rust. More recently, rose rosette disease has become a serious threat as it continues to spread among cultivated roses in the US.