Final answer:
Herbaceous ornamentals can be affected by diseases caused by bacteria, fungi, and viruses, with symptoms varying from discoloration to the formation of galls. Economic losses can occur as a result of these diseases, particularly when they impact crop quality and quantity.
Step-by-step explanation:
Diseases of herbaceous ornamentals can include a range of disorders caused by interactions with various organisms such as bacteria, fungi, water molds, nematodes, and viruses. The Phytophthora species, which cause diseases like sudden oak death and affect plants such as rhododendrons, azaleas, and potatoes, are one example. The development of a disease often follows the disease triangle concept, which depends on the environmental conditions, host susceptibility, and pathogen virulence.
Plant viruses such as tomato spotted wilt virus, bean common mosaic virus, and cucumber mosaic virus can cause symptoms including cell necrosis and hyperplasia, leading to issues like malformed leaves and galls. On ornamental plants like roses and peonies, viruses like rose mosaic virus and peony ring spot can produce discolored splotches and ring spots on the leaves. The severity of these diseases can lead to significant economic losses in both agriculture and landscaping.