Plant Health Problems

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 chlorothalonil, copper sulphate pentahydrate, mancozeb, 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, copper sulphate pentahydrate, 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:

Cutworms.
Certain kinds of cutworms occasionally feed on the leaves and flowers of pansy plants in greenhouses and cold frames. Small cutworms that feed at night and are coiled up in the soil around the plants during the day have caused considerable injury. The plants may be sprayed with acephate, carbaryl or chlorpyrifos, which are among the compounds registered for control of this pest in Connecticut. Consult the label for dosage rates and safety precautions.

Garden slugs. Limax maximus.
Garden slugs often injure pansy plants. Greenhouses, as well as moist, shaded outdoor gardens, are sometimes infested by garden slugs. These slugs are molluscs with no shell. They feed mostly at night, eating notches in the margins and holes in the interior of tender leaves. They leave a slimy, iridescent trail wherever they crawl. During the day, they hide under rubbish.

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 newly set plants will control slugs by rupturing their epidermis. Placing a small board in the flowerbed for the slugs to hide under during the day makes it easy to destroy many at one time. A bowl of beer, sunk into the ground, with a roof to protect from sun and keep large animals out, will act as a bait and the slugs will drown. If necessary, chemicals such as metaldehyde, which is among the compounds registered for use against this pest in Connecticut, will control slugs. Consult the label for dosage rates and safety precautions.

Greenhouse or Celery leaftier, Udea rubigalis.
This insect has been recorded to have caused severe injury to pansy under glass. Although this small greenish-white striped caterpillar may occasionally feed on leaves, it is not a serious pest and control is rarely needed.

Imported longhorned weevil, Calomycterus setarius.
The grayish adults are about 1/8" long. They emerge from late June through July and early August. Eggs are laid in the soil, and larvae are present from mid-summer until June of the following year. They feed on the small roots of host plants but more often on those of legumes or on organic matter. Both wild and cultivated plants are attacked. Usually, the adults feed on the upper surface at the edge of the leaves and on flowers. Host plants include annuals, perennials, shrubs, deciduous trees, and evergreens. Drenching insect pathogenic nematodes around the roots may control larvae.

Violet gall midge, Phytophaga violicola.
Adults are small, mosquito-like flies. Small maggots feed within a pocket formed by the edge of the leaf curling downwards around them. The misshapen leaves are susceptible to rotting, and flowers fail to develop. Pick off and destroy infested leaves. Imidacloprid, which is registered for use against this pest in Connecticut, applied as a soil drench, may be effective. Consult the label for dosage rates and safety precautions.

Violet sawfly, Ametastegia pallipes.
Leaves of pansies and violets are sometimes eaten by bluish-black, smooth larvae 1/2" long with white spots. At first, the lower surface of the leaves are skeletonized. Larger larvae eat holes through leaves. Injury is most noticeable in late spring. There may be several generations during the growing season. Insects may be handpicked when occurring in small numbers. Among the compounds registered for control of this pest in Connecticut are acephate, carbaryl, insecticidal soap, spinosad or malathion sprayed when the larvae are first observed to protect the foliage, or imidacloprid used as a soil-applied systemic. Consult the labels for dosage rates and safety precautions.