It seems that this column has become the bearer of bad news. Two weeks ago it was about blotchy bottomed tomatoes and last week it was the Tomato Hornworm. This week it's all about downy mildew on impatiens.
Don't confuse downy mildew with powdery mildew. Powdery mildew occurs as a white powdery coating on leaves of dogwoods, lilacs, roses, phlox, beebalm, squash and many other plants in landscapes and gardens. The appearance of powdery mildew in gardens in mid- to late summer is an annual event, though not one to be celebrated.
On the other hand, downy mildew of impatiens is a new disease to Massachusetts, having first appeared just last year. The disease is very specific, infecting only impatiens, not including New Guinea impatiens. Local landscape gardeners have reported finding the disease on bedding impatiens in many gardens here in Berkshire County.
Downy mildew begins as a slight yellowing of leaves followed by development of a white mildew on the underside of leaves. As the disease progresses, the leaves fall off, leaving only naked stems -- not a pretty sight.
Sadly, there is nothing home gardeners can do to prevent or cure the disease. However, where the disease has occurred, impatiens should be pulled up, bagged and disposed of. Since the soil is most likely contaminated, bedding and double impatiens should not be replanted in the same site for at least a couple of years.
On that glum note, let's turn our attention to happier events:
- Go out and enjoy the lavender blue spikes of Russian sage (Perovskia atriplicifolia). This silvery leafed perennial has become very popular in landscapes since it tolerates poor soils and sunny, dry sites. The flowers which appeared in mid-July are long-lived, often lasting until first frost of fall. The flowers can be cut for indoor arrangements.
- Pull up onions when at least half of their leafy tops have turned brown and flopped over. Air-dry the onions for 2 or 3 weeks, and then cut off the tops an inch above the bulb. Store the onions in mesh bags, milk crates, or peach baskets in a cool, dry place.
- Harvest leeks as needed but leave the rest in the garden to continue growing. Leeks will remain green through fall and even later if mulched heavily once freezing weather sets in. Mulched leeks may be harvested throughout the winter if the ground is not frozen.
- Keep weeding! Even with the harvest season in full swing, weeding remains a primary gardening activity because seed heads of most weeds have matured. If these weeds are not removed, those seeds will be deposited in your garden soil, creating what's called a seed bank. Unfortunately, this seed bank has more deposits than withdrawals. A single weed plant is capable of producing thousands of seeds.
- Consider sodding rather than seeding a new lawn area that is on a slope. If installed properly, sod will quickly stabilize soil on the slope and prevent erosion. Keep in mind that soil preparation for sodding is the same as for seeding.
- Give some thought to becoming a Master Gardener. The Western Massachusetts Master Gardener Association, a non-profit educational organization dedicated to promoting good and sustainable gardening practices, is now recruiting potential Master Gardeners for their upcoming training session beginning in Janu ary 2013. For an application and more information, call Laura Du mouchel at 413-743-7976 or email her: firstname.lastname@example.org.