Impatiens have long been the most popular shade-loving annual for the Kansas City market. But the arrival of downy mildew to the area is causing us to rethink the use of this old-time favorite. It’s been spreading across the country the last few years and finally was confirmed on impatiens in this area last summer. Now that it is here, what should we do?
Downy mildew of impatiens survives in the soil for an indefinite period of time. Most recommendations are to not replant impatiens in areas where downy mildew has been detected.
Downy mildew first appeared in local gardens following the cool, rainy and humid period last August. Symptoms include leaf yellowing followed by what appears to be a wilting effect. Plants infected while young will be stunted. Humid conditions will allow a white coating to appear on the underside of the leaves, which is caused by the spores of the fungus.
Infection can be passed by water splashing from nearby infected plants or spores that have overwintered in the soil. Infected plants will not recover and fungicide sprays are not reliable to protect healthy plants. Once it appears in an area it does not go way. The spores remain in the soil.
Prevention is the key. Impatiens downy mildew is encouraged by wet leaf surfaces, shade and crowded plantings. To help reduce the spread into your garden: purchase only healthy plants; reduce crowding by increasing spacing between plants; and avoid overhead watering, especially in the evenings and at night. Also, don’t be in such a hurry to plant in early May. This plant will do best, and establish better, once the soils have warmed. A mid-May planting time is best to help reduce the disease. Once you have a problem with downy mildew of impatiens the planting area is probably doomed for more impatiens.
To read more on this topic or to get your gardening questions answered on The Star’s KC Gardens blog by Dennis Patton and other Extension experts, go to KansasCity.com/gardens.