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:
Leaf spots, Phomopsis or Septoria spp.
Leaf spots are very common, typically sharply delimited necrotic areas on plant leaves caused by a wide variety of pathogenic species. Leaf spots usually are favored by wet conditions and may become important if a large number of lesions are present or if they start to coalesce.
Under those conditions, control may also be achieved with the use of fungicides applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are thiophanate-methyl and sulfur. Consult the label for dosage rates and safety precautions.
Powdery mildew, Erysiphe spp.
These fungi are obligate plant parasites which grow vegetatively on the plant leaf surface, sending haustoria, structures which absorb food from the host, into epidermal cells. The white mildew seen on the leaf is a combination of vegetative mycelium and spores borne in chains on upright conidiophores. Wind-dispersed mildew spores can germinate without free water under high humidity conditions, and disease is often severe when conditions are humid but dry. Small black over-wintering structures called perithecia are often found in powdery mildew affected areas.
Control may also be achieved with the use of fungicides applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are potassium bicarbonate, ultra fine oil, sulfur, triadimefon, or thiophanate-methyl fungicides. Consult the label for dosage rates, safety precautions, and directions for use.
Rust, Coleosporium or Puccinia spp.
The term rust refers to both the disease and pathogen causing the disease. Rusts are specialized obligate parasites which can cause disease on one (monoecious) or two (heteroecious) host species. Symptoms of rust infection include rust-colored spores or gelatinous horns in powdery pustules on leaves or stems. Surrounding tissue is discolored and yellowed, and plants are often stunted.
Control of heteroecious rusts may be aided by removal of the alternate host, but for most perennials, control may also be achieved with the use of fungicides applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are sulfur and mancozeb. Consult the label for dosage rates, safety precautions, and directions for use.
Stem rot, Sclerotinia sclerotiorum.
Symptoms include yellowing of lower leaves followed by wilting and death of the rest of the plant. A white cottony mass of mycelium growing around the crown or on the soil near the crown distinguishes this crown rot from others. In this fungus web may be found the whitish to cream color or buff or reddish-brown seed-like sclerotia the size of a pinhead.
Control may include removing and destroying all infected plant parts and removal of topsoil around the plant. New soil may replace sclerotia-filled soil.
Wilt, Verticillium dahliae.
This pathogen infects the vascular or water-conducting tissues of plants, and causes wilt symptoms by impairing water flow. As a result, symptomatic plants may flag or wilt on one side of the plant, leaves may be twisted and yellow on one side, turn brown and hang down prior to drying up. Overall, the plant exhibits drought symptoms despite adequate soil moisture. If the stem is cut open near the base, the vascular tissues are typically brown or discolored.
Wilt control involves removal of infected plants and associated roots and soil. The pathogens survive in soil and plant debris for long times, so disposal of plants and soil without spread is important.
Liatris is not affected by insect pests. See Perennials.