Groff's Plant Farm Images

Downy Mildew Update

Published: Thu Jul 13th 2017

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The summer of 2012 was a bad one for impatiens lovers.

These shade-loving, colorful plants were the #1 flower for shade, and one of the top five most commonly grown annuals in the United States. Then disaster struck.

Downy Mildew was first discovered that winter in Florida. Impatiens there are planted in the fall as a “winter annual” and they started dying in large swaths. The spores blew up the East Coast on the wind or hitched a ride from propagators in the South.

Downy Mildew is technically a water mold that causes a fluffy white network of mycelium under the leaf surface. Leaves first yellow, then curl slightly, the mold becomes visible and the leaves fall off leaving bare impatiens skeletons. Spores are thought to persist in the soil for 3-5 years.

By August of 2012, there were documented cases from Maine to Florida and as far west as Chicago. Landscapers in New Jersey were especially howling as many commercial properties needed to be replanted. Many homeowners also lost lovely planting under their trees.

The next year growers panicked. Many drastically reduced the number of plants they were growing for the 2013 season or discontinued them completely. This was quite a blow to the #1 shade annual. But gardeners and greenhouse growers are resilient and faced with the choice of nothing, or try something new, many tried something new.

This was a great opportunity for plants like torenia (wishbone flower), coleus, begonias and New Guinea impatiens which are all resistant to the fungus, to shine. Breeders quickly kept new plants coming down the pipeline and choices of beautiful blue or purple browallia (pictured above), new interesting foliage plants, colorful caladiums and upright fuchsias quickly took center stage. A seed strain of New Guineas lowered the price point so there were even New Guineas being sold in market packs like the regular bedding impatiens.

Here it is 5 years later. Many growers have cautiously brought impatiens back. Last summer there were very few reported cases. But landscapers for the most part are still staying away. If you had trouble in 2012, trying them in pots has been successful. But the king of the shade has been dethroned. Many homeowners have discovered there are very good alternatives and growing a diversity of plants lessens your general risk of disease.


**This article was written in July.  By late August reports of the disease started coming in again.  Looks like we are not out of the woods yet.