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:
Basal or root rot, Rhizoctonia solani or Pythium spp.
Roots and basal stems are rotted, black or brown and collapsed. Sunken lesions may occur at the soil line. These fungi must be distinguished microscopically. However, Pythium tends to predominate in wet soils and Rhizoctonia in well-drained soils.
Control with fungicides is not reliably effective and may be prohibitively expensive, so removal of infected plants is important.
Downy mildew, Peronospora, or Phytophthora spp.
These pathogens typically cause leaf spots with downy white or gray patches under the leaves. The downy growth results from the production of spores called sporangia which are wind-dispersed between plants. Disease is usually favored by cool wet weather.
Control may include cultural means of reducing humidity and leaf wetness. 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 is mancozeb. Consult the label for dosage rates, safety precautions, and directions for use.
Gray mold, flower and leaf blight, Botrytis cinerea.
This fungus occurs everywhere and commonly infects senescing or damaged plant parts such as old flowers, causing a fuzzy gray mold. Spores are produced which are easily blown around. From these tissues the fungus moves into healthy stems and leaves, causing a damaging blight. Disease is favored by cool wet conditions and the presence of overripe fruit or old flower petals.
Sanitation is the most important means of control. Remove dead flowers before gray mold develops. If disease has moved into leaf or stem parts, 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 is thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Leaf spots, Alternaria, Colletotrichum, Diplodia, Septoria or Stemphylium 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 or Microsphaera 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, Puccinia or Uromyces spp.
The term rust refers to both the disease and pathogen causing the disease. 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 or root rot, Sclerotium or Fusarium.
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.
Diseases caused by Viruses:
Mosaic, Ringspot, or Tomato spotted wilt, viruses.
A number of different viruses can attack perennials. These viruses are obligate parasites which are not themselves alive, but use plant cell metabolism to replicate and produce more virus. Symptoms of infection are commonly loss or mottling of color, yellowing, yellow rings, stunting, and/or deformed leaves, flowers or buds. Viruses can be transmitted by mechanical means such as touching or rubbing leaves with hands or tools contaminated by contact with diseased plants, by dodder, nematodes, grafting or insects such as aphids, leafhoppers, whiteflies or thrips.
Control is based on starting with virus-free stock or seeds, control of insect vectors, eliminating weed virus hosts, resistant varieties, and eliminating diseased plants.
The leaves of lupines are frequently infested with the aphid, Macrosiphum albifrons. Spraying with ultrafine horticultural oil, insecticidal soap or malathion, which are among the compounds registered for use against this pest in Connecticut, will control them. Consult the label for dosage rates and safety precautions.
Garden millipedes, Julus hortensis.
These arthropods resemble wireworms because the body is cylindrical. However, there are many legs. They are from 1 1/2 to 2" long and brown in color. These animals usually feed on decaying organic matter, but sometimes attack living plants.