Odds may be in our favor for impatiens this year; you can help researchers

healthy impatiens by Stofko
Healthy impatiens walleriana. Photo by Connie Oswald Stofko
Impatiens showing early signs of downy mildew. Photo courtesy Margery Daughtrey

 

by Connie Oswald Stofko

What are the odds your impatiens will do well this year?

Well, we had a drought last summer, so that’s good. The dry weather inhibited the spread of downy mildew, which is the blight that has been plaguing  Impatiens walleriana, the plant that shade gardens had come to know and love for decades.

Then again, our spring has been wet and cool, which are conditions that help the disease thrive, said Margery Daughtrey, senior extension associate with the Section of Plant Pathology and Plant-Microbe Biology at Cornell University.

On the other hand, our local growers have been treating impatiens before they sell the plants, and that treatment should protect the plant for a month from the time the treatment was applied.

Then again, we don’t know what the weather will be like the rest of the summer. Cool, wet weather encourages the growth of the disease, but hot, dry weather could keep your impatiens healthy longer.

We’ll go through some reasons why you might or might not want to plant impatiens in your shade garden this year. If you do plant impatiens, there are some things you can do to increase your chances of keeping your plants healthy.

But if your impatiens do develop downy mildew, there’s a way you can help researchers.

Be a citizen scientist & help research into downy mildew

Impatiens with downy mildew. Photo courtsy Margery Daughtrey

Mark Bridgen is doing research, hoping to find plants with the ability to resist downy mildew. Bridgen is director of the lab that Daughtrey works in, the Long Island Horticultural Research & Extension Center. These researchers need help from gardeners.

While the researchers have dried samples, they need live samples of impatiens with downy mildew. So if your impatiens plants get the disease, the silver lining is that you could help with the research.

Watch your plants for symptoms of the disease. You might see early signs, such as yellowing leaves, like the single plant in the second photo. If you see the white coating on the backs of the leaves, like in the third photo, that’s downy mildew.

If you really want to help, you could purposely plant impatiens in a spot where you have had downy mildew in the past, increasing the chances that the plant will get the disease.

If you think your impatiens has downy mildew, put a bucket over the plant (so the disease doesn’t spread), but don’t pull the plant out. Email Daughtrey at mld9@cornell.edu and she will tell you what she needs.

The Long Island research center has hundreds of seedlings that the researchers are working with, and efforts are going on at seed companies as well to breed disease-resistant impatiens, Daughtrey said.

“People are working toward a better impatiens,” she said, but cautioned, “It won’t happen overnight.”

There’s also a related plant, Impatiens balsamina, also sometimes referred to simply as balsam, that can also get the disease, and Daughtrey would like samples from that as well.

Balsam is sort of an old fashioned plant that might not be as popular as it once was. Instead of mounding like Impatiens walleriana, it grows upright in a spike and has pointed leaves. Impatiens balsamina is susceptible to the disease, but it isn’t killed outright like regular impatiens is.

On balsam, instead of a coating on the back of the leaves, you’ll see small spots on the leaves. Again, if you find the disease, contact Daughtrey at mld9@cornell.edu.

How to increase the odds of keeping impatiens healthy

Note that there is nothing that the home gardener can spray to prevent or to treat downy mildew on impatiens. Seriously, nothing.

However, there are a few things that you can try to increase the chances of keeping your impatiens healthier longer. Here are some tips from Daughtrey:

  • Because cool, wet weather helps the disease along, you could delay planting. Wait until the weather is warmer and drier rather than dash out earlier in spring.
  • If you had the disease affect your plants before, don’t plant impatiens in the same spot.
  • Heavy rain can splash the disease spores about 30 feet, so if you have had the disease in your garden and want to try impatiens again, plant at least 30 feet away from where the diseased plants were located.
  • Plant your impatiens in hanging baskets. Keeping the leaves dry and allowing air circulation may keep the disease at bay longer. Planting impatiens in containers and setting them on a porch or other area with a roof where they are shielded from rain may help. When you water plants in containers, you tend to water the soil rather than spray the leaves, which can be beneficial. In addition, impatiens in a hanging basket may benefit from better air circulation.

You can plant some impatiens, but Daughtrey encourages you to avoid a monoculture. Plant other things as well. Learn about some alternative plants for the shade. A newer alternative is ‘Bounce’.

To plant or not to plant

First of all, if you want to plant impatiens, go ahead. It’s not sinful, Daughtrey said. You’re not hurting the environment.

The disease has affected a wild plant called jewelweed since at least the 1800s, she noted. The spores that cause the disease exist in the soil for years. Even if no one planted impatiens in their landscape, the disease would still exist in wild areas. It will never completely leave.

Every plant has its Achilles heel, she said. Roses get black spot, but we still plant roses. If you want to plant impatiens, go ahead.

The downy mildew problem isn’t as severe now as it was in 2012, 2013 and 2014. Back then people were buying plants that already showed the symptoms of disease, Daughtrey said, because there wasn’t awareness of the disease.

For several years, now, local growers have been treating impatiens, so at least when gardeners bought the plants, they were healthy. (Last year there were some diseased plants in the greenhouse trade in southern states, Daughtrey said, but she didn’t see problems in New York State.)

So we have all that going for us.

Here are some things to keep in mind when deciding whether to plant impatiens:

  • If you have planted impatiens in the past and have had problems, your chances of again having problems are higher. On the other hand, if you haven’t had problems, your chances of having problems are lower, though it could still happen.
  • How unhappy will you be if your impatiens die? Some gardeners don’t want to take the chance that the flowers they lovingly planted will die from disease. They would rather choose other plants. Other people are willing to take the chance.
  • Even if your impatiens plants eventually die from the disease, they might look healthy through August. Would that be long enough for you? Some gardeners can accept that because by August they are ready to replace summer annuals with mums anyway.

Background on impatiens and downy mildew

If you have a shady garden, you know that there aren’t many pretty flowers that grow in shade. That’s why gardeners used to love impatiens (specifically, Impatiens walleriana.) They grow in an attractive mounding shape, come in a variety of colors and are relatively inexpensive.

They would bloom all summer.

But in 2012, a blight called downy mildew hit Western New York, quickly killing affected plants. There aren’t any treatments that a home gardener can apply. If the plant gets the disease, the plant will die. Check out the fact sheet on impatiens and downy mildew that Daughtrey co-wrote.

The disease doesn’t affect surrounding plants.

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9 Comments on “Odds may be in our favor for impatiens this year; you can help researchers

  1. I’ve noticed a powdery covering on several patches of lamium. I usually pull it out when the flowers are done to keep it from spreading too much but don’t recall it getting powdery. I gave up on impatiens a long time ago because they seemed “over-done”!

  2. Yes, everyone with a shade garden used to use impatiens! I’m not sure what is affecting your lamium, but it’s probably not the same thing that affects impatiens.

  3. Thank you so much on this article. It was very helpful. And I give a huge thumbs up to Mischler’s and Goodman’s on their stance to only sell quality product. I’m excited to go out and explore finding the new “Bounce” plant.

  4. Thank you for this update. I had been wondering if it was safe to buy them again, but it looks like I won’t be able to plant them in the garden again.
    Using containers is a great idea to still enjoy them for awhile. I now use New Guinea impatiens exclusively. More expensive but long lasting,lush & reliable.

  5. Thanks for getting the word out, Connie! I really am interested in hearing about any findings of downy mildew on Impatiens walleriana…I’ve noticed that many people have planted it this year here where I live in Riverhead — I think they simply got tired of waiting for the disease to go away! Just email to me at mld9@cornell.edu if you find plants with that disease! One comment to Meredith above: there IS a downy mildew that affects lamium, so if you see fuzzy coatings on the undersurface of the leaves, that might be why. It might be one called Peronospora lamii… you can see where that downy mildew got its species name. Fortunately it doesn’t seem to faze lamium much at all…the plants keep coming back. It is obviously quite a different disease from the impatiens downy mildew.

  6. For all of you watching and waiting: downy mildew has been fostered by our wet rainy spring, and has shown up on the east end of Long Island, in Saratoga Springs and in Lockport this year. Symptoms of very stunted growth followed by white sporulation on the undersurfaces of leaves have shown up on plants grown in flowerbeds where the disease was known to occur in earlier years—additional evidence that oospores in the soil will keep this disease around! I’ve heard of no cases in Buffalo yet: keep your eyes peeled and let me know if you see it, please!

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