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, Alternaria, Cercospora, or Colletotrichum.
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, Sphaerotheca 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. 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.

Insect Problems:

Aphids.
Two aphid species, Aphis gossypii and A. nerii, feed on butterfly weed. A. gossypii is usually dark in color, while A. nerii is bright yellow with dark legs. Sprays of horticultural oil, insecticidal soap or malathion, or a soil drench of imidacloprid, are among the compounds registered for use against these pests in Connecticut. Consult the label for dosage rates and safety precautions.

Red milkweed beetle, Tetraopes tetrophthalmus.
Both the 1/2" long adult and larva feed on butterfly weed, or milkweed. The elytra, or wing covers and pronotum are red with smaller black spots on them. The compound eye is divided in half by the antennae. Adults stridulate, or produce squeaking sounds, when captured.

Monarch butterfly, Danaus plexippus.
The larvae of this well known orange and black butterfly eat butterfly weed foliage. Control is unnecessary.