Costa Farms Fights Downy Mildew

Check out the impact downy mildew had on these impatiens.

Costa Farms, a bedding and indoor houseplant grower in North America, is working to get ahead of the downy mildew disease that is infecting Impatiens walleriana or standard garden impatiens.

“Downy mildew is only infecting Impatiens walleriana,” explains Dr. Kate Santos, director of research and development for Costa Farms. “Gardeners can be assured it is not infecting other plant species like New Guinea impatiens and SunPatiens.”

Plasmopara obducens, the type of downy mildew that’s attacking impatiens, has been reported in several states and made its first appearance in the Palm Beach County area of Florida in late 2011. At this time, downy mildew cannot be cured after it is detected; prevention is the only way to protect impatiens from the disease.  

“The best defense is a strong offense, so we at Costa Farms have initiated a three-prong approach to alert people about the disease, prevent infestation and provide alternatives to have healthy, beautiful plants in their landscape,” explains Santos. “We’re determined to help contain and minimize the spread of this disease.”

Know The Symptoms
The time from infection to the appearance of symptoms varies from about 5 to 14 days. To protect your crop, know how the disease is spread and be on the lookout for early leaf symptoms of the disease, especially in young plants and new growth.

According to Laura Sanagorski and Bill Schall, environmental and commercial horticulture extension agents at the University of Florida’s IFAS Palm Beach County Extension, young plants and new growth are most susceptible to the disease.

“The signs are yellow or light green foliage with speckling on the infected leaves, and then a white, downy-like growth composed of spores visible on the underside of the infected leaves,” Santos says.

Santos also warns that the first sign might be a downward leaf curling. If unchecked, eventually the leaves and flowers will drop, resulting in bare stems with only a few tiny, yellow leaves remaining, she says.

Weather also plays a role in the spread of downy mildew. “Cool temperatures, moist air and wet foliage are ideal conditions for the disease that is spread by air or water movement,” says Santos.  

Protect Through Prevention
Sanagorski and Schall also suggest that prevention is the most effective management strategy. They recommend eliminating nighttime watering and excessive fertilization to help avoid or reduce the occurrence of the disease.

“If infected impatiens are discovered, immediately remove the entire plant-roots, leaves and top part of plants, put into a plastic bag, tie it off and dispose,” Santos says.

Costa Farms is currently utilizing preventative measures that will protect its crops from downy mildew for several weeks after leaving the farm.

“Consumers can feel confident that Costa Farms is employing every measure to protect the plants prior to leaving the farm,” Santos says. “We’d like to remind consumers to only plant impatiens in beds that have not previously shown symptoms of downy mildew.”

Find Flower Alternatives
The good news is there are plenty of bedding plants that are ideal replacement for standard impatiens.

“If your impatiens are in the shade, you may lean to begonias or New Guinea impatiens, and if your garden is in the sun, plant SunPatiens, phlox and petunia or lobelia,” Santos says. “Remember to check your bedding impatiens, and use alternative flowers to create that wow color you love for your garden this year.”

For more information or to see a gallery of alternative flowers, visit

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