Impatiens Downy Mildew Incidence Down Significantly In 2013

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Impatiens downy mildew leaf yellowing and downward curling

With more than half of the country impacted by impatiens downy mildew in 2012, it’s a bit of a relief to hear that – so far – confirmed reports of the disease appear to be much lower in 2013. According to a presentation by Ball Horticultural Company’s Colleen Warfield and Cornell’s Margery Daughtrey at OFA Short Course, only Florida, Louisiana, Texas, California and most recently Missouri and Kentucky have confirmed reports in both greenhouses and in the landscape. A number of other states have reported the disease in greenhouses, but in most cases, it doesn’t seem to have made its way out into the landscape there.

It’s unclear why the disease hasn’t developed as widely this year, but increased awareness among growers, retailers and consumers may have helped blunt the spread of the disease.

One new wrinkle has been the discovery of infection in a species other than Impatiens walleriana: Impatiens balsamina. Balsamina is a plant that’s widely distributed in eastern U.S. and comes back in the spring. Infection causes a yellowing of the leaves, rather than complete plant collapse. There’s both good and not so good news in this discovery. Since plants come back, they can bring back the disease as well. This is a potential reservoir host outdoors that is keeping the disease out there. On the plus side, balsamina does have at least some level of resistance to the pathogen so it will be of interest to breeders and possibly help breed resistance into commercial walleriana varieties.

USDA is looking for a better understanding of impatiens downy mildew and other diseases and has started a program to collect samples from across the country. If you come across a plant infected with impatiens downy mildew (or boxwood blight, rudbeckia downy mildew, sunflower downy mildew or brown rust of mums), visit OrnamentalPathology.com to find out how to share a sample.

Richard Jones is the group editor for Greenhouse Grower and Today's Garden Center magazines.
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    4 comments on “Impatiens Downy Mildew Incidence Down Significantly In 2013

    1. pat bellrose

      st. louis mo. had no cases until around july 10. Now I have heard of 4 cases. Wipes the plants out in a matter of days can send pictures if you like

    2. M Zach

      Omaha, NE We planted over 1500 Impatiens Wallerina. Have just disposed of over a third of those because of Downy Mildew.

    3. bobbie robison

      impatiens in four beds were fine until week of Aug 12 – just pulled all of them out in hopes of preventing spread. suburban chicago – had lots of rain until beginning of july and then things got very dry.