Plant Health Problems
See Perennials for a detailed discussion of problems that may occur and are common to most herbaceous ornamentals.
Diseases caused by Fungi:
Fusarium wilt, Fusarium oxysporum var. barbatus.
Leaves of infected plants appear flaccid, have curled edges, and hang down. This is frequently followed by a general yellowing, wilting, and death of the entire plant. When the stem is cut, a brown discoloration or streaking may be visible in the vascular tissues.
Control of this disease is difficult since the pathogen is commonly found in soil. One of the key strategies for control of vascular wilts is prevention. Therefore, it is important to avoid planting sweet-william in infested soil. It is also helpful to maximize plant vigor by good cultural care and watering. Careful handling of plants will avoid root injury which enables the fungus to enter the plant. Since repeated use of the same area greatly increases the amount of disease, rotation is essential. When available, it is also helpful to use resistant varieties. Chemical controls are not effective for these fungi.
Stem rot, Rhizoctonia solani.
The above-ground symptoms of this are nonspecific and include a general yellowing, wilting, and collapse of the foliage and the entire plant. Dark lesions are sometimes visible on the stem at or near ground level.
Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the crown area of the plant. Highly symptomatic plants can be rogued and removed since recovery is unlikely.