Plant Health Problems
Diseases caused by Fungi:

Anthracnose, Colletotrichum antirrhini.
Symptoms appear as tan, oval lesions on the stems. When numerous, they coalesce and girdle the stems resulting in the death of the stem above the lesions. Lesions may also develop on the leaves.

Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are maneb and mancozeb. Consult the label for dosage rates and safety precautions.

Gray mold, Botrytis cinerea.
Flowers turn a papery brown and become covered with gray, fuzzy masses. Senescing flowers are particularly susceptible. Tan to brown spots with a target-like appearance can also develop on the leaves. These patches are often associated with flowers which have dropped onto the leaf surface. This disease is particularly troublesome during periods of extended cloudy, humid, wet weather.

Good sanitation practices including grooming the plants and removing spent or senescing flowers can minimize the potential for infection. These affected tissues should be carefully removed and discarded when they are dry. It is also important to avoid wetting the flowers when watering and crowding plants. Adequate spacing between the plants can promote good air circulation. Use of fungicides is usually not necessary. However, control can be enhanced with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are iprodione, chlorothalonil, mancozeb, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Rust, Puccinia antirrhini.
Early symptoms of infection appear as chlorotic spots on both upper and lower leaf surfaces, stems, and other plant parts. Diagnostic symptoms then develop and can readily be seen as pustules that break open to reveal the rusty-brown spores for which this disease is named. Heavily infected plants shrivel and die.

This disease can be minimized by cleaning up plant refuse in the fall and by adequate spacing of the plants to promote good air circulation. Use of rust-resistant varieties wherever possible is also very helpful. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are mancozeb and maneb. Consult the label for dosage rates and safety precautions.

Root and stem rot, Rhizoctonia solani.
The above-ground symptoms of this disease are usually nonspecific and include a general wilting, decline, and collapse of the foliage and the entire plant. This general droopiness or flaccid appearance is often accompanied by browning and rotting of the roots and the crown. Darkened or discolored lesions can develop on the main stem near the soil line. Yellowing and death of the outer leaves follows, until finally the entire plant is dead.

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.

Leaf spots, Colletotrichum, Cercospora.
Symptoms vary with the causal agent. With Colletotrichum, symptoms look like frog-eyes and appear as tan spots with distinct light eyes. These can be quite large and up to ½ inch in diameter. With Cercospora, symptoms appear as small, tan spots with purple margins.

Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are chlorothalonil, mancozeb, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Powdery mildew, Erysiphe.
White, powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot, humid weather. Heavily infected leaves turn brown and shrivel.

Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, sulfur, potassium bicarbonate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Downy mildew, Peronospora antirrhini.
Early symptoms of infection often go unnoticed and appear as slightly chlorotic areas on the upper leaf surface. Diagnostic symptoms develop as the fungus grows and breaks through the lower leaf surface and appears as a purplish-gray fuzzy growth. When infection is heavy, leaves shrivel and die.

Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. This disease can be minimized by cleaning up plant refuse in the fall and by adequate spacing of the plants to promote good air circulation. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut is mancozeb. Consult the label for dosage rates and safety precautions.

Diseases caused by Viruses:

Impatiens necrotic spot, virus (INSV).
Symptoms can appear as round, necrotic spots on leaves. This virus is transmitted by the western flower thrips.

Control of this disease is focused on prevention since once plants are infected, they cannot be cured. It is important to eliminate and remove infected plants as soon as they are recognized and to eliminate other symptomatic plants since this virus has a very broad host range. It is also critical to manage the thrips population.

Insect Problems:

Cyclamen mite, Phytonemus pallidus.
The cyclamen mite often injures snapdragon. This translucent, microscopic mite often infests the new leaf and blossom buds, and can proliferate on spent blossoms. Characteristic injury includes dwarfed, thickened and wrinkled leaves. On azalea, dahlia, and other plants with stems, the distance between internodes becomes drastically shortened. Infested plants do not bloom, or blossoms may be misshapen. Cyclamen mite is not easily controlled when mature plants are badly infested: effective miticides are not available to homeowners, so a commercial applicator may be required for effective miticide applications. Effective restricted use materials are abamectin (requiring three sprays), dicofol, and endosulfan. Consult the label for dosage rates and safety precautions.

Green peach aphid. Myzus persicae.
When needed spray with ultrafine horticultural oil, malathion or insecticidal soap. See aphid fact sheet.

Twospotted spider mite, Tetranychus urticae.
This pest infests the undersides of the leaves, which become light yellow in color, and the plants have a generally unhealthy appearance. Sometimes the mites form webs, which more or less enclose the upper as well the lower leaf surface. Among the compounds registered for control of this pest in Connecticut are insecticidal soap and ultrafine horticultural oil. Spraying with insecticidal soap will give sufficient control if applied at least twice at 7-10 day intervals. The predatory mite, Neoseiulus fallacis, is most commonly found feeding where there are mite infestations. A single application of ultrafine horticultural oil (1/2 - 1% dilution) can be effective if predatory mites are present. Special care should be taken with soap or oil to obtain thorough spray coverage, because they only work on contact. Commercial growers may consider using hexythiazox or abamectin (a restricted use product). Consult the label for dosage rates and safety precautions. Avoid applying carbaryl or pyrethroids, which tend to be much more toxic to the predators than to the pest spider mites.