Diseases caused by Fungi:
Botrytis blight, 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.
Fusarium wilt, Fusarium oxysporum f. sp. cyclaminis.
Symptoms of this disease can develop at any stage of plant growth. Leaves may appear yellow, wilt, and collapse. Some plants may show no signs of infection until they come into flower, when they suddenly collapse. Diagnostic symptoms can occasionally be seen when the stem is cut to reveal a purple, reddish-brown to black discoloration of the vascular system in the crown.
Control of this disease is difficult once plants are infected. Therefore, the key strategy for control of vascular wilts is prevention. It is important to avoid planting cyclamen in infested soil. It is also helpful to maximize plant vigor by good cultural care and watering. Careful handling of plants will avoid root injury which enables the fungus to enter the plant. Since repeated use of the same area greatly increases the amount of disease, rotation is essential. Resistant varieties are not available at the present time. Chemical controls are not effective for this fungus.
Diseases caused by Viruses:
Impatiens necrotic spot, virus (INSV).
Symptoms appear as round, brown, necrotic spots on the leaves. Brown or yellow ringspots can also develop and a browning of the petiole end of the leaf has occasionally been reported. This pathogen 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 in close proximity since this virus has a very broad host range. It is also critical to manage the thrips population.
Diseases caused by Nematodes:
Foliar nematodes, Aphelenchoides.
These plant-parasitic worms attack virtually all plant parts and may cause leaf lesions, yellowing, necrosis, and leaf drop. Leaves and stems can collapse or the plant may not produce normal buds. Lower leaves first show brown wedge-shaped areas between the veins which eventually involve the entire leaf. Discoloration then progresses from the bottom to the top of the plant. The nematodes live and move in water films.
Reducing leaf moisture by avoiding overhead irrigation and removal of infected tissues, debris, or plants are important for control.
Black vine weevil, Otiorhynchus sulcatus.
The grubs devour the small roots, or burrow within the cyclamen corm. The tops of injured plants wilt and often die. Leaf notching by adults can also be unsightly. The 1/2" long adult weevil is black, with a beaded appearance to the thorax and scattered spots of yellow hairs on the wing covers. Only females are known, and the adults are flightless. They feed nocturnally, notching the margins of the foliage. The legless grub is white with a brown head and is curved like grubs of other weevils. Adults and large larvae overwinter, emerging from May - July. The adults have to feed for 3-4 weeks before being able to lay eggs. Treating the soil with insect pathogenic nematodes may control the larvae and is a sensible approach for house plants and landscapes.
Cyclamen mite, Phytonemus pallidus.
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 products include abamectin, dicofol, and endosulfan. Consult the label and follow all safety precautions. Hot water treatment at 120F for 15 minutes controls cyclamen mite on corms.