Zinnia Sclerotinia

Asked August 20, 2019, 6:48 PM EDT

Over the last two years I planted borders of Zinnia profusion backed by Dahlia Tahoma Hope backed by assorted Bee Balm. It’s been a beautiful long season show but this year Sclerotinia has fairly decimated the zinnia beds. I determined Sclerotinia with the help of plant expert from Shorty’s Nursery. The fungus was in one border until August but now showing up in additional borders that form a half circle at the gardens entrance. Info on treatment is sporadic at best. I’m only finding Wikipedia’s take on the topic with a nod towards fungicide without directions on application. I’d appreciate any ideas. The garden has a historically limited pallete of plants. The color parade has been outstanding so of course we’d like to continue with Zinnias. No other plants in these borders seem to be affected. Thank you, Robb Rosser write2robb@gmail.com 503-381-3576

Clark County Washington

1 Response

FIrst of all, I would suggest that the diagnosis may be incorrect. My suggestion to you would be to take a sample of the plant--pull up an entire plant, preferably, and take it into the Clark County Master Gardener Plant Clinic. They can take a look at it, and if necessary, can send it to our WSU plant pathologist in Puyallup for a definitive diagnosis.

Call (564) 397-5711
Heritage Farm/WSU Extension Plant Clinic Office
1919 NE 78th Street, Vancouver, Washington.
Hours for walk-in clients:
Tuesday and Wednesday • 10 A.M. to 2 P.M.
Thursday and Friday • 11:30 A.M. to 3 P.M.
However, I've researched sclerotinia or white rot of zinnia. PNW handbooks states that there is no fungicide registered in Washington for home use. I rechecked again on WSU's PICOL (Pesticide Information Center Online), and got the same result. However, there is some cultural information on controlling the disease.
  • Make sure the plants have good air circulation because crowding creates a good environment for fungal disease.
  • Remove and destroy all the affected zinnias.
  • Rotate your flower crop for 3 full years with plants that are less susceptable to the disease, such as alyssum, daffodil, salvia, pansies, or ornamental grasses.
Here is the article from NW Plant Disease Handbooks. Keep in mind that the fungicides listed in the article are NOT available for home users and are intended for commercial operators only. https://pnwhandbooks.org/plantdisease/host-disease/zinnia-stem-rot Good luck!