Gerbera daisies (Gerbera jamesonii) are easy-care annuals that grow up to 18 inches tall. They require little more than full sun (at least six hours each day) and well-draining soil to produce abundant, large blooms in red, pink, orange, yellow or white. Gerbera daisies also attract birds, butterflies and bees to the garden while remaining resistant to deer. However, there are a few diseases and pests gardeners may run into when growing gerberas.
Also called “plant lice,” aphids measure only about 1.5 to 4 mm long, may be either winged or wingless, and are black, green, brown, red or yellow. Aphids suck gerbera daisies’ sap, weakening the plant. They also leave behind excrement called honeydew, which may lead to disease.
Aphids are notoriously difficult to get rid of once they are well-established, so it’s smart to inspect plants regularly for them. Spraying aphids with a blast of cold water from a garden hose is the best treatment; repeated sprays may be necessary. Pesticides for controlling aphids may also be applied, but according to the University of California Agriculture and Natural Resources Program, they will kill beneficial insects, too.
Gerbera daisies are susceptible to gray mildew (also called "gray mold"), especially when the weather is humid or damp. This fungus attacks dead parts of the plant, but can spread throughout the living plant and eventually kill it. Gray mildew can be prevented by removing spent blooms and brown leaves promptly, according to the University of Florida Extension.
Adult leaf miner flies measure about 2 to 2.5 mm long and have a yellow head, and black and yellow body with brown wings. The larvae are orange-yellow. The insect feeds on gerbera daisy leaves by “mining” into them, leaving behind a black line. If the larva has left the leaf, a half moon will appear on one end of the tunnel. Leaf miner infestations weaken gerberas and reduce their flower production. The University of Florida Extension recommends removing and destroying infested leaves. Chemicals like acephate or paraffinic oil may also be used, but they will only be effective early in the infestation.
When the weather is humid or gerberas are overcrowded, they are prone to powdery mildew. This fungus gives leaves and other plant parts a dusty white or gray look, and it can lead to decreased flower production, distorted plants, and in severe cases, plant death. Cornell University suggests using fungicides labeled for powdery mildew.
Like aphids, whiteflies weaken gerberas by feeding on their sap, leaving behind honeydew that may lead to disease. Adult whiteflies measure about 0.8 mm long, have four wings, and are white.
Begin by isolating infected plants. According to the University of Missouri Extension, whitefly traps or the use of a small handheld vacuum can help control small infestations. Chemicals are largely ineffective against whiteflies.