White Spots on a Clover Houseplant

Symptoms

• As its name suggests, powdery mildew leaves a white, powdery dusting of mold on stems, leaves and flowers of infected plants. Early stages appear as white spots. These spots may eventually coalesce and cover entire leaves and plants. Severely infected leaves can become distorted or curled.

Disease Cycle

• Powdery mildew is an infection caused by a fungus. These fungi are host specific and can only feed on living plant matter. Outdoors the fungus appears in spring when cool, moist conditions favor its spread. Indoors these conditions can be met at any time. The white growth is comprised of a network of threads and reproductive spores that are spread via wind. In the case of houseplants, air ducts or fans can help spread the fungus.

Cultural Control

• Following some good cultural practices can help keep your plant from succumbing to the infection. Keep your plant in a place with good ventilation to ensure leaves dry easily. Water in the morning so foliage has a chance to dry before temperatures drop at night. Drought-stressed plants are susceptible to powdery mildew, so keep your shamrock in moist, well-drained soil. Pruning out severely infected leaves may help prevent the disease from spreading.

Chemical Control

• There aren't many fungicides suitable for a houseplant, according to Iowa State University, and disposing of infected plants may be the best option. However, shamrocks can be planted outdoors, so fungicides rated for outdoor plants may work if the plant is transplanted outside. Fungicides are most effective when used at the earliest sign of a problem. Always read the label instructions before applying fungicides.