Impatiens Downy Mildew: Is It Time Yet?

Impatiens Downy Mildew: Is It Time Yet?

How To Overcome Downy Mildew Spread On Impatiens

Exhibiting the stems-only stage Daughtrey describes in the story above. Photo courtesy of Margery Daughtrey, Cornell University.

A number of retailers recently asked me if they could start selling bedding impatiens again. The number of complaints were way down. People were not seeing nearly as many problems with impatiens downy mildew, and the demand (and pressure) on wholesalers and retailers was still very strong. The question in a nutshell was, β€œIs it time yet?”

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Retailers and landscapers, more in the South than North, remember a plant called Red Tips (photinia). It was a ubiquitous shrub that was used in almost every landscape and residential site wherever it was hardy. You could not drive a block without seeing beautiful, red-tipped hedges or groups of plantings on restaurant, golf course and residential properties.

Then one year, a leaf blight (Entosporium) started, and with such a dense population, it spread rapidly. Airborne and soilborne spores made the disease particularly successful.
Within five years, nearly all the Red Tips had been removed. It was sad to see such beautiful plantings so decimated, but equally sad that retailers and growers lost such an important and profitable plant. There were no substitutes that provided the rapid growth and colorful foliage. Red Tips never recovered.

Fast forward 10 years. Today I do see some Red Tips here and there, and they are healthy and make a glorious display, as they always did. A few retailers are selling them again, essentially saying there are no problems with Red Tips in the neighborhood β€” maybe it has passed. Pathologists and plants people will say there are few problems because there are few Red Tips. The sheer size of the population made infection easy, rapid and extreme. Those left standing may have some degree of resistance, but are healthy mainly because the germplasm population is under control.

Has Enough Time Passed For Bedding Impatiens?

The situation is similar with Impatiens walleriana. Fortunately, not every region has been infected with downy mildew, but for those that have, it has been too short of a time period between the pandemic and reintroduction. There are fewer problems in infected areas because most retailers and growers stopped selling/producing impatiens, and the host population dramatically fell.

So here are my thoughts for 2015 on bedding impatiens in a non-perfect world.
1. Breeders are trying to breed for resistance. This does not happen overnight and is likely a few years away.
2. Growers, breeders and retailers should continue to look for substitutes in begonias, New Guinea impatiens and other genera. Breeders who can come up with a seed-propagated New Guinea impatien that remains short, tolerates shade and flowers well will be golden.
3. If retailers must sell bedding impatiens, recommend planting them in containers and baskets only. This will not prevent infection if there are lots of spores floating around, but it will slow it down. People may not pay attention to your recommendations, but you are educating them as best as you can.

Bedding impatiens are too important to disappear like Red Tips. They are far easier to hybridize, trial and work with than a woody shrub. I am confident breeding, selection and proper management will reduce the severity of the impatiens gap in good time, but no, it is not yet time to put them in the starting lineup.

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Phyllis says:

Thank-you co much for your answer..I have been planting impatiens in flower pots and in ground soil for over 18 years…Until of course for about 4-5 years I have stopped because of the downy mildew. My Mom also planted them forever. In fact when my husband was in the Navy and we lived in Va. Beach I planted them in the ground in front of my house they bloomed and were breathtaking beautiful…in fact a few people actually stopped their cars and pulled over to ask me what kind of hedges they were…they were astonished when I told them they were not hedges they were impatiens…I do miss planting them….Phyllis

Vince Carnett says:

Thank you! I just today sat down to research what was going on with my impatiens the past few years, I figured it was some bug eating them. Such a shame, has always been a wonderful shade plant.

Tom and Julie King says:

We live in the Chicago area and have been growing impatiens for decades. We first encountered downy mildew in 2012. That year, our impatiens were pretty much destroyed by mid summer. However, before they all died, we harvested seeds from the strongest plants and planted them the following year. The 2013 crop lasted till early August. We did the same thing the next year and they lasted a little longer. It’s now August 29, 2015 and our impatiens still look beautiful. Maybe the downy mildew scourge is over? Hopefully!

HarryS says:

In Chicago area back in 2014, I lost my impatients, even those in hanging planters. I thought it was over fertilization. Halfway thru the replanting in 2015, I learned about downy mildew, so I interspersed with begonias. I had one plant droop in July. I removed it and sprayed the rest with fungicide. No further losses, and the bed bloomed til September, This year in 2016, I decided to be bold and plant half the beds with impatients.