Impatiens downy mildew has shown up already in NYS greenhouses. It is appearing in double impatiens and also appearing in the standard bedding plant cultivars, even in relatively resistant varieties.

Consider keeping vegetatively-propagated impatiens cultivars separate from seed-grown types until you can be sure they are not infected. Remember how easily this disease spreads?

 

Check your impatiens for off color leaves and turn the leaves over to see the white fuzzy mycelium on the back (picture at end of message)

 

Also see https://s3.amazonaws.com/assets.cce.cornell.edu/attachments/2564/DM-homelandscape2-2.pdf?1409319821 for pictures of symptoms. Dispose of (carefully – the spores are airborne so don’t spread the disease on the plant’s way out) infected plants.

 

There are fungicides that can be used as protectants – even for the resistant cultivars if you have found impatiens downy mildew in your greenhouse. Remember – protectants work BEFORE the plants are infected.  Margery Daughtrey suggests Segovis and Stature and Segway as among the most reliable.  Other fungicides have had some resistance issues with impatiens downy mildew.

 

More information at:

http://www.egroblog.com/showblog.php?ID=132

https://s3.amazonaws.com/assets.cce.cornell.edu/attachments/2561/E-GRO_2_06.pdf?1409319731 (this resource is from 2013 so use more recent pesticide information)

 

A more general statement on downy mildews:

The downy mildews are a group of oomycetes (AKA water molds) that are for the most part limited to a few host genera or to a family of plants.  So don’t expect downy mildew on rose to spread to your snapdragons. One of the most important of these diseases, Impatiens downy mildew, is limited to just the genus Impatiens, with hosts including the regular bedding plant as well as the double-flowered forms used in hanging baskets. Fortunately, though, the downy mildew of Impatiens walleriana does not bother the New Guinea Impatiens, Impatiens hawkeri.

 

Greenhouse Crops That Commonly Get a Downy Mildew Disease

Impatiens

Coleus

Rose

Snapdragon

Viola

Basil

Rosemary

Sage

Strawflower

Alyssum

Agastache

Stock

Salvia

Sunflower

Cleome

Ornamental Kale

Ornamental Cabbage

 

Herbaceous Perennials That Commonly Get a Downy Mildew Disease

Rudbeckia

Digitalis

Hellebore

Agastache

Coreopsis

Scabiosa

Iberis

Geum

Veronica

Nicotiana

Geranium (hardy)

Aster

Viola

Lamium

Lamiastrum

Salvia

 

Woody Plants That Commonly Get a Downy Mildew Disease

Buddleia

Viburnum

Rose

 

Betsy