Gerbera plants are members of the sunflower family that are grown as annuals in the northern part of the United States (US) and perennials in the southern part. Gerberas bear daisy-type flowers in shades of pink, red, orange, cream and yellow. The leaves are long, lobed and clumped together. Gerbera daisies are commonly used in mixed flower beds and butterfly gardens. The gerbera is susceptible to several diseases.
Powdery mildew (Erysiphe cichoraceaum) is the most common gerbera disease. This fungal disease is prevalent during long periods of high humidity, moderate temperatures and cloudy weather. This disease first causes small blotches of a powdery, white substance to appear on the flowers and lower leaves. Some gerbera plants develop a brown, scab-like lesion. Powdery mildew progresses quickly, and the affected gerbera plants dry up and die. Powdery mildew pathogens spread to other gerberas through air currents.
Botrytis blight, also known as gray mildew, is caused by a mold fungus (Botrytis cinerea). Botryitis infections typically attack gerbera plants during extended periods of rainy, cool weather. Affected plants develop a gray, fuzzy growth that contains masses of fungal spores. This blight can develop on any part of the gerbera plant except for the root system. The fungus overwinters in dead plant tissue and then spreads to live plants by air currents.
Black Root Rot
Black root rot (Thielaviopsis basicola) is a fungal disease that damages the gerbera plant's root system. Above-ground signs of black root rot include yellowing of the newer growth and wilting leaves. Some affected plants develop black stem lesions at the soil line. The diseased roots appear black, gray or off-white, according to the severity and age of the disease. The black root rot pathogens are soil-born and can survive for years in tiny spores called chlamydospores.
Most gerbera diseases can be avoided by proper plant care. These plants need well-drained soil and should be watered only when the top soil is dry to the touch. Overhead watering methods shouldn't be used because they can cause excess moisture. Gerberas should be planted 12 to 18 inches apart to allow for correct air ventilation. The crowns should be just above the soil line. Potting media should be disinfected to eliminate any infectious organisms.
Infected gerbera daisies should be removed from the vicinity of other plants. Blighted or faded blossoms, blighted leaves and other infected plant parts should be burned or placed in a plastic bag. Infected plants should never be used on a compost pile. Fungicidal sprays might help control gerbera diseases caused by fungal spores when applied in the early stages. When fungicides are applied as foiliar spray, the foliage absorbs the chemicals and moves it down into the roots.