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:

Crown rot, Sclerotium delphinii.
Plants wilt and die and are covered at ground level with white mold containing seed-like sclerotia which range from buff to reddish-brown.

Removal of dead plants and the surrounding soil that contains sclerotia is otherwise indicated. If sclerotia are not found, the causal organism may be Rhizoctonia solani. Planting in uninfested soil will avoid both troubles.

Downy mildew, Plasmopora pygmaea.
This pathogen typically causes 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.

Leaf spot, Septoria spp.
Leaf spots are 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 polygoni.
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. (monoecious and heteroecious).
The term rust refers to both the disease and pathogen causing the disease. Rust fungi 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.

Wilt, Verticillium albo-atrum.
Plants are slow growing and small. Lower leaves yellow, and plants wilt and die. Black streaking in vascular bundles of stem indicate infection by one of these fungi.

Planting in uninfested soil will prevent this disease. Once present in a garden other susceptible species may contract the disease if put in the same location. Use of clean soil is indicated.

Diseases caused by Bacteria:

Bacterial leaf spots, Pseudomonas delphinii.
Irregular water-soaked spots become brown or black. Leaves may turn yellow and drop.

Remove diseased plants and debris as noticed. Avoid overhead irrigation, especially in the evening and increase air flow through the plants to speed drying of the foliage.

Diseases caused by Nematodes:

Root-knot nematodes, Meloidogyne hapla.
The northern root-knot nematode, M. hapla, is a sedentary endoparasite, meaning that it infects host roots after hatching from eggs, stimulating the formation of a small gall containing specialized feeding cells, and feeds in the same location through several molts to produce several hundred offspring. Because most of its life cycle is inside roots, it may be spread to new locations with vegetative propagation material. This nematode is parthenogenetic, a single female can reproduce without males, resulting in a new generation every 28 days under ideal conditions. The galls produced on roots interrupt translocation and act as a nutrient sink. As a result, plants may be stunted, wilt easily, and show signs of nutrient deficiency. The nematode has a wide host range, but a number of ornamentals, including Rudbeckia, Aster, and others, have been shown to be resistant.

Growing resistant plants or rotating to small grains can greatly reduce or eliminate nematode populations in infested soil.

Insect Problems:
See Perennials.