DEAR READERS: I'm hearing from so many of you who are concerned in the wake of my report on the fate of impatiens on Long Island. As difficult as it may be to accept, it is expected that the widely planted and well-loved annual will be affected by downy mildew if planted again next year, as the disease not only will survive winter in the soil, but also travels from plant to plant via airborne spores. To answer your most common questions, I reached out to Margery Daughtrey, senior extension associate at Cornell University's LI Horticultural Research & Extension Center.
Q: What can I treat my soil with to eliminate a disease recurrence?
There is nothing that can be used to treat soil as an antidote to this disease. If you want to try to grow impatiens next year, plant them in different beds because the downy mildew makes spores that survive in the soil. Only steam-sterilization could eliminate them from the soil -- or time, but we don't know how many years the spores will last. For next year, we know it is unwise to put them back in the same place.
Q: I already composted my infected impatiens. Can I use the compost?
Compost to which infected impatiens have already been added could be used in vegetable or flower beds where you aren't trying to grow impatiens next year. Composting with careful, thorough technique is always best: Make sure all parts in the pile get exposed to the heat by turning the pile over, not just throwing the dead plants into a pile in the corner of the yard.
Q: Other plants (dusty miller, grass, etc.) situated near my impatiens died at the same time. Did downy mildew kill them, too?
Different organisms attack the different species of plants; they don't just spread indiscriminately from one kind of plant to another. This particular disease is caused by a downy mildew called Plasmopara obducens, and it cannot attack dusty miller, grass, roses or anything else, except some of the impatiens species, including Impatiens walleriana (the bedding plant impatiens) and Impatiens balsamina (the balsam impatiens). Even the close relative Impatiens hawkeri (New Guinea impatiens) does not get the disease.
The reader with the dusty miller death probably had a situation of overwatering, drought or Rhizoctonia stem rot. The lawn problem is also not connected, except that the grass experienced the same stormy muggy weather as the impatiens did, and those kinds of environmental conditions are very conducive to the development of many different fungal diseases, including downy mildew. There is probably a different fungal disease on the lawn.
DEAR JESSICA: Help! We are inundated with horrible voles. They are destroying my gardens. Everywhere we walk, there are tunnels. We've watched our hosta disappear inch by inch into the underworld. We have tried so many things. What works, besides moving? --Carole Rosenthal, Smithtown
DEAR CAROLE: Voles, as you've noticed, spend a lot of time carving curvy tunnels in lawns and gardens. They don't live long, but they make the most of their short lives by reproducing and eating grass, seeds, bark, sedges, potatoes, beets and other roots, tubers and plants. They can girdle the trunks and roots of some trees and can kill plants altogether by disturbing their roots. The most effective means of eliminating voles is with ordinary mousetraps baited with apple chunks, placed where you spot activity.