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Violet (Viola)

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:

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. Control can also be achieved with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are mancozeb, chlorothalonil, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Root and crown rots, Rhizoctonia solani, Thielaviopsis basicola.
The above-ground symptoms are 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. Yellowing and death of the outer leaves follows, until finally the entire plant is dead. Blackened stem lesions may be present at or near the soil line.

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 plant. Highly symptomatic plants can be rogued and removed since recovery is unlikely. Attention to spacing is also helpful since it improves air circulation between plants and promotes drying.

Powdery mildew, Sphaerotheca.
White powdery spots or patches develop on leaves and occasionally on petioles. 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.

Anthracnose, Colletotrichum.
Symptoms appear as small, circular spots with purple-black borders. These can develop on leaves, stems, or flowers. When infection is heavy, entire plants may be killed.

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 and mancozeb. Consult the label for dosage rates and safety precautions.

Scab, Sphaceloma violae.
This disease can be quite disfiguring when infection is heavy. Symptoms appear as somewhat irregular, scabby, tan lesions which can develop on leaves, stems, sepals, or any green part of the plant. When the stems are girdled by the lesions, entire plants can topple over 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. 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.

Leaf spots, Alternaria, Cercospora.
Circular to irregular tan to brown spots develop on leaves. These can vary in size, color, and number, depending upon the causal agent.

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 mancozeb, chlorothalonil, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.

Rust, Puccinia violae.
This is the most common disease of Viola in Connecticut. Symptoms first appear as pale green spots on the upper leaf surface. As the fungus grows within the leaf, diagnostic symptoms develop and can be seen on the under leaf surface. These appear as corky spots, blisters, or pustules which break open to reveal the rusty-brown spores for which this disease is named.

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 are maneb and mancozeb. Consult the label for dosage rates and safety precautions.

Downy mildew, Peronospora violae.
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 Nematodes:

Foliar nematodes, Aphelenchoides spp.
These plant-parasitic worms attack virtually all plant parts and may cause leaf lesions, yellowing, necrosis and leaf drop, and bud malformation. Plants often appear dwarfed and leaves at the growing tip are distorted. Stems of infected plants may appear swollen and the internodes are shortened.

Since these nematodes live and move in water films, this disease can be minimized by reducing leaf moisture by avoiding overhead irrigation and by providing adequate spacing of the plants to maximize drying of the foliage. It is also helpful to remove infected tissues, debris, or plants.

Insect Problems:

Aphids.
The violet aphid, Micromyzus violae, and probably also the green peach aphid, Myzus persicae, occasionally infest violet. Among the compounds registered for control of this pest in Connecticut are insecticidal soap, ultrafine horticultural oil or malathion. Imidacloprid applied as a systemic also controls these aphids.

Bagworm, Apterona helix.
The larvae of this moth construct a tiny, helix-shaped, silken bag to which they attach soil particles. From the larger opening they feed on the underside of violet foliage, while pushing frass out the smaller opening at the opposite end. The clear epidermal layer, which may eventually fall out, is left after feeding. They also feed on cucurbits, corn and forage crops. There is one generation each year with the larval, feeding stage, lasting the longest. Only females are known. Eggs are laid within the bag, which is also where pupation occurs. When needed, they can be controlled with the use of Bacillus thuringiensis var. kurstaki, acephate, or spinosad which are among the products labeled for control of this pest in Connecticut. Consult the label for dosage rates and safety precautions.

Garden slugs.
Garden slugs, molluscs without a shell, usually infest moist, shaded gardens. Hosta and violets are particularly attractive to slugs. Slugs feed mostly at night, rasping holes in tender leaves or along leaf margins. Recent slug damage is easily recognized from the slimy, iridescent trail left by their crawling. At maturity they can be up to four inches long. They lay clusters of eggs, encased in slime, in the fall. Slugs can be controlled by lightly cultivating the ground in the spring to destroy dormant slugs and their eggs. A band of diatomaceous earth put around new plantings will control slugs by rupturing their epidermis. During the day, slugs hide in dark and moist places, so they can be trapped by placing a small board in the flower bed for them to hide. Scrape the slugs off the board and into soapy water to kill them. A bowl of beer, sunk into the ground with a roof of some sort, will act as a bait and the slugs will drown. Metaldehyde bait is registered for control of this pest in Connecticut. Consult the label for dosage rates and safety precautions.

Violet gall midge, Phytophaga violicola.
The small fly or midge lays white eggs in the curled margins of the unfolded new leaves. These eggs hatch, and the maggots remain in the curled margins, causing greater curling, distortion, and twisting of leaves. There are probably several generations annually in greenhouses. If this pest becomes a problem for home gardeners, handpicking and disposal of affected leaves should take care of the situation. Imidacloprid applied as a systemic may also control these midges. Consult the label for dosage rates and safety precautions.

Violet sawfly, Ametastegia pallipes.
The leaves of violet plants in the garden are often eaten at night by blue-black larvae with whitish tubercles. These larvae hide under the lower leaves or in the soil during the day. When full grown they are about 1/2" long. The adult is a black sawfly about 5/8" long that lays eggs in blister-like incisions in the leaves. There is only one generation each year. Spraying larvae with spinosad or malathion will be useful in controlling this insect. Several treatments may be necessary. Alternatively, apply imidacloprid as a systemic to be taken up by the roots.

Yellow woollybear, Diacrisia virginica.
The caterpillars sometimes feed upon violet. Whitish, yellowish, or brownish hairy caterpillars feed upon the leaves of verbena and many other kinds of plants in the garden in late summer. This caterpillar is about 2" in length when fully grown and is covered with long hairs that vary in color from pale yellow to reddish brown. It makes its cocoon of its own hairy coat and silk, hiding in sheltered places, sometimes 20 to 30 being clustered together. The insect overwinters in this stage and the moths emerge in June and July. The moth has a wing spread of between 11/2 and 2", and is pure white with a few black dots, blackish antennae, and orange abdomen with a row of black spots on the back and along each side. Handpicking is the usual means of control.