Low-maintence impatiens may still need saving from downy mildew

My impatiens just crashed — they rather quickly turned yellow and lost all their leaves. I thought impatiens were supposed to be easy to grow. What can I do to avoid this from happening again?

— Alfredo Nunez, Highwood

Your description indicates that you have had downy mildew on your impatiens. Downy mildew of impatiens has been observed in the United States since about 1994 but became more widespread and destructive around 2011. Most gardeners stopped planting common impatiens around that time due to the high probability of the plants being attacked by downy mildew. The disease affects common impatiens (Impatiens walleriana), while New Guinea impatiens,(Impatiens hawkers) are highly resistant to the disease. Some symptoms of downy mildew of impatiens include new leaves that are small or discolored (yellow or pale green), stunted growth overall with yellowish foliage, flower buds that fail to form, leaves curled downward and a fluffy, white fungal covering on the lower surface of the leaf. As the disease progresses, the plants will become barren stalks with one or two yellow leaves left. Keep in mind that letting young impatiens consistently dry out can result in stunted plants with yellow leaves, so be sure to consider how the plants have been maintained before diagnosing downy mildew. If caught soon enough and adequate watering resumed, the “dry” plants will quickly recover while downy mildew-infected plants will continue declining.

I have had success planting Beacon ® impatiens, which were developed by PanAmerican Seed to be highly resistant to downy mildew. Look for Beacon on the plant labels to make sure you are buying this disease-resistant series, developed after years of breeding and plant pathology work in the Netherlands. There are currently eight colors of Beacon: bright red, violet shades, lipstick, salmon, coral, orange, rose and white. Beacon impatiens reach a mature height of 14 to 18 inches and spread 12 to 14 inches. Plant them 8 to 10 inches apart after the chance of frost has passed in the spring. Spacing the plants out properly will help allow air movement between the plants, which will help reduce humidity and leaf moisture that foster downy mildew. The initial planting may seem too thin, but the plants will quickly fill in. Go ahead and replant your impatiens now if you can find Beacon impatiens.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.