America’s best selling annual for shade, impatiens (impatiens walleriana),
the colorful, reliable annual you know and love in both single and
double flowered forms, is being threatened by a disease called Impatiens Downy Mildew. IDM has been a problem in Europe for many years, and is slowly
crossing the U.S. from east to west, appearing last August as close as
Evanston and Downer’s Grove. Plants look fine at the beginning of the
season, then a light green yellowing or stippling of the leaves appears,
followed by a white, downy growth on the underside of leaves under
cool temperatures and moist or humid conditions. Eventually the leaves
and flowers drop, leaving bare stems, and also leaving spores behind
in the soil. The spores are wind-borne as well. There are as yet no
chemical controls. Plants that look healthy at the beginning of the
season can show disease later. To top it off, spores in the soil may
mean it is unsafe to plant impatiens in the same spot for 8 to 10
years.Growers are in a quandary in the face of this major threat to their business. However, they are producing flats of impatiens for 2013, though in curtailed numbers. They can guarantee that their stocks are disease free in the greenhouse, but cannot guarantee that they will not get IDM later in the season. The Garden Fair’s annuals department will also cut back on numbers of flats, depending partly on feedback from the public.
We’d really like to know if this disease has reached Hyde Park. If you think you had the problem described above, please report it to Bam Postell.
Precautions
- If you think you had this problem last year, do not plant impatiens in the same location.
- One of our growers thinks impatiens in hanging baskets may fare much better than in-ground planting, because they are planted in fresh soil, and their location up off the ground will provide better air circulation.
- In beds or in baskets, water in the morning so that the plants will be dried off by nightfall.
Substitutes for your shady areas
- New Guinea Impatiens--a different species and NOTsusceptible to IDM, has colorful foliage as well as brilliant flowers; it is nearest in habit to bedding impatiens.
- Begonias--wax, tuberous Non-Stops, angel-wing, rex--all types.
- Coleus--foliage in more dramatic color combinations than ever.
- Hypoestes, “Freckle Face,”--a good foliage plant for shade; pink, rose, red, or white splashes on green; insignificant flowers.
- Iresine and Perilla--red-toned foliage plants for shade.
- Torenia, “Wishbone Plant”--a dainty annual in purple tones, intriguing flowers.
- Salvia splendens--the old-fashioned scarlet poker types and the Salsa series (same species, same flower type), in ivory, purples, salmon, burgundy and red.
