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Impatiens Downey Mildew



DUE TO THE SEVERITY OF THIS DISEASE WE WILL NO LONGER BE CARRYING IMPATIENS WALLERIANA.  WE DO NOT FEEL IT IS RIGHT TO OFFER THIS PLANT TO OUR CUSTOMERS KNOWING THAT THERE IS A VERY STONG POSSIBILITY THAT IT WILL DIE IN THE LANDSCAPE AFTER ANY FUNGICIDE PROTECTION WE APPLIED IN THE GREENHOUSE WEARS OFF.  PLEASE SEE OUR PLANT AVAILABILITY LIST FOR OTHER APPROPRIATE SUBSTITUTES  FOR IMPATIENS IN YOUR GARDENS.

What is impatiens downy mildew?

Impatiens downy mildew, caused by Plasmopara obducens, is a new disease to our area. It infects impatiens walleriana, which includes common seed varieties of impatiens as well as vegetative varieties like double impatiens. It also infects balsam impatiens and native impatiens known as jewelweed. This has not affected New Guinea impatiens or Sun impatiens.

What are the symptoms?

The symptoms start with a slight yellowing of the plant. As the disease continues the plant will become completely yellow and leaves may curl downward. If conditions are favorable for the disease a white downy growth will develop on the underside of the leaves. Favorable conditions include wet foliage, cool temperatures (especially at night) and moist air.

What should you do if you have it in your flowerbeds?

Infected plants can not be saved. Fungicide treatments on healthy looking plants may be affective if the plants have not already been infected. These treatments will need to be continued throughout the growing season and are not a guarantee that the plant will not become infected.

Infected plants, along with roots and all plant debris should be bagged and thrown away. Do not compost infected plants, the disease may over winter in your compost pile.

Beds that have had impatiens downy mildew or that have been exposed to it should not be planted with impatiens for several years. The disease produces two types of spores, one that is easily dispersed by wind and one that may over winter in the soil for several years.

 

Where do we go from here?

The impatiens varieties that are affected by this have been a major part of our landscape for many years. They have offered us an economical display of color that few other plants can offer with the same minimal care.

Despite the place impatiens have had in the past it is our opinion that this is now “part of the past” and other plants will have to replace impatiens until varieties with resistance to this disease are developed.

What are the planting options for beds that have been infected with impatiens downy mildew?

For people that want a similar looking plant for a shady garden New Guinea impatiens are resistant to impatiens downy mildew. Sun impatiens tolerate more sun and are also resistant to impatiens downy mildew.

Other plants that can be used for shady areas:

Begonias – both tuberous and fibrous rooted.

Browallia

Lobelia

Torenia

Coleus – Coleus is not affected by impatiens downy mildew but is susceptible to a different type of downy mildew that affects only coleus.

For a sunny location flowering vinca offers a similar look with better sun and heat tolerance.

All other plants, other than Impatiens wallerina, can be planted in beds that have had infected impatiens in them.

Excerpts from UMASS Extension Center for Agriculture bulletin “Impatiens Downy Mildew In Home Gardens”

For additional information about impatiens downy mildew go to:

 

extension.umass.edu/landscape/sites/.../impatiens_downy_mildew.pdf

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