Newspaper article The Florida Times Union

New Disease May Make Impatiens Tough to Find

Newspaper article The Florida Times Union

New Disease May Make Impatiens Tough to Find

Article excerpt

Byline: Terry Brite DelValle

Shady areas begging for color are often planted with impatiens every spring. They are often planted in drifts under the shade of pines. This year it may not be so easy to find this garden favorite due to a disease problem.

Downy mildew (Plasmopara obducens) of impatiens (Impatiens walleriana) is a new disease to Florida and was found in Palm Beach County at the end of 2011. This disease has been found in other parts of the U.S. and in Europe and is known to cause widespread destruction to impatiens. Luckily, New Guinea impatiens (Impatiens X hawkeri) and SunPatiens are tolerant of the disease.

This disease is classified as a "water-mold" and is favored by cool, moist conditions. The disease is spread by two different types of spores. One (zoospores) moves through water and can also be carried by wind in a sporangium. The second type is of most concern, the oospores. This forms inside the leaf tissue and can be persistent in the soil. Fruiting spores most commonly infect young growth, so once leaves age and temperatures heat up plants are less susceptible.

Symptoms are similar to other types of downy mildew. Initially infected leaves are slightly chlorotic or off-color and may be speckled. There may be subdued gray lines on the tops of leaves and leaf edges curl downward. As the disease progresses, the chlorosis (yellowing) becomes more severe and infected leaves fall off along with flowers, leaving naked stems. The underside of affected leaves often has a white to gray downy growth that contains the reproductive spores. Eventually, the entire plant will collapse. By this time, the disease has spread to the entire planting and it is unknown at this time how long the disease may persist in the soil under Florida conditions.

LANDSCAPE MANAGEMENT

This disease has not been identified in our area, but it is only a matter of time before it rears its ugly head. Avoid introducing this disease into your landscape by inspecting and selecting healthy plants for your landscape. If you are lucky enough to find impatiens this year, wait to install plants once the weather is consistently warm at night. …

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