Impatiens Downy Mildew Found in Louisiana

Characteristics of impatiens downy mildew include discoloration of the upper leaf and downy mildew growth on lower leaf surfaces.

Impatiens downy mildew, a scourge of the summer bedding plant across the northern United States, has made its first appearance in Louisiana.

The infected plants, found by plant pathologist Don Ferrin, were purchased at two different national chain store garden centers, supplied by wholesalers from two neighboring states, according to the New Orleans Times-Picayune. Inspection of both garden centers' remaining stock confirmed the presence of downy mildew.

The mildew often initially appears as a gray discoloration on new growth, or a yellowing or downward curl of the leaves. Airborne spores that spread the disease will grow on the underside of infected leaves and appear as a white, powdery growth. Frequent overhead irrigation can spread the pathogen; if overhead irrigation is unavoidable, experts recommend watering in the morning so the leaves can dry quickly.

Impatiens walleriana are most susceptible to the mildew, while New Guinea impatiens are tolerant; however, the latter strain is less tolerant of heat and are more prone to root rot. If discovered, infected plants, fallen leaves and plants in the immediate vicinity should be uprooted and destroyed, as symptoms may not be visible for up to two weeks.

More information on identifying, preventing and managing impatiens downy mildew can be found in an article at endowment.org.