Downy Mildew of Impatiens – Buyer be aware

A “new” disease is on the horizon – and attacks one of the most popular annual plants sold for shade areas – the Impatiens. Downey Mildew, as the name implies, is a fungal type disease, and easily travels from plant to plant by spores. The spores are transferred by wind, from the soil by watering or rain, use of contaminated containers or equipment, or even by touching infected plants.

This disease, which has been on the east coast now for a few years, hits greenhouses hard, as an entire crop can be wiped out in the matter of weeks. The disease was spotted in the Des Moines area in 2013 and will most likely make an appearance in our area soon.

Healthy Impatiens plants can be affected in a short period of time. Symptoms include yellowing and slight curling of leaves, with white mildew on underside of leaves; then flowers and foliage drop off, leaving bare stems. Remove and bag any infected plants immediately.

Fungicide use is not recommended as is not completely affective, and will not eliminate mildew spores from the soil, which can remain and overwinter for several seasons. Remove and bag any infected plants, including roots, immediately.

What to do? Select other shade-loving type plants to fill your containers and flowerbeds; be creative and try something new this year. Perhaps ageratum, coleus or begonias or ask a local Master Gardener for ideas on those less common bedding plants, such as Heliotrope, Torenia or Alternanthera.

Did you know? This disease only affects the common-type Impatiens (Impatiens walleriana). The New Guinea type impatiens (Impatiens hawkeri),are not affected, and may be a good replacement choice.

For further information on selecting plants or other gardening questions, contact Yvonne McCormick at yvonne@iastate.edu