Now we have gorgeous 50 degree sunny days – this is my kind of winter weather. I even went out to my veggie garden and pulled out some chickweed/dead nettle out of the strawberry patch. Barely made a dent but it was satisfying anyway.
I have been hearing frequently this fall and winter about these two disease issues, so here’s what I understand about 2 prevalent problems in landscape flowers that might affect us gardeners this year.
Impatiens disease
A downy mildew is infecting Impatiens walleriana (common shade Impatiens) and possibly some wild Impatiens in 32 states or more as of the fall of 2012, mostly east of the Mississippi River. There is debate about whether there are effective chemical controls right now.
Certainly for homeowners, an IPM (Integrated Pest Management) approach will be most useful.
[Integrated Pest Management is an attitude towards plant health whereby we look at the whole picture before reaching for a sprayer. Consider these components in any a problem situation: Horticultural requirements like shade/sun tolerance and pH and nutrition needs; abiotic causes meaning what might have caused the problem that wasn’t a disease or insect; weather, storms, etc that might be contributing; human and pet impact; identify symptoms before making conclusions – sometimes an insect pest or a browning of a plant came after some other injury or malady.] [Just one example: There’s a lovely shade bed full of Hosta and in April the gardener notices dozens of holes in the foliage. Gardener does a careful inspection and can find no insects in sight. But there was a hail storm the week before. One very likely explanation!]
IPM for Impatiens downy mildew calls for rotating crops in planting beds, possibly preventative fungicides, and removal of affected plants. Some nurseries are effectively using fungicides on their market plants. This will not provide protection from spores remaining in soil from past infected plantings.
Note that you cannot identify the infected plants by sight, so buying a healthy looking plant at the garden center doesn’t mean the mildew won’t appear later.
For most homeowners, unless you want to spray a fungicide weekly, it’s easier to try planting a new variety of bedding plants this year. For shade beds, try New Guinea Impatiens, which are suggested as disease resistant, or try annual Begonias, or Hypoestes. Vinca (annual) may do well in mixed sun/shade beds…hey, you could even migrate to perennials: some smaller Hosta and Hardy Begonias will provide a full ground cover, though with not quite the color coverage of Impatiens.
Rose Rosette Disease
Rose Rosette disease has been showing up in roses for several years but is now being talked about frequently in the nursery and landscape industries.
• All types of roses are susceptible but shrub roses (including Knockout roses) are particularly prone.
• Rose rosette is a viral disease, spread by mites, which are most active spring to September.
• Symptoms are: deformed leaves and flower buds, excessive reddish foliage, thick clusters of small stems (“witches broom” effect) , and unusually thorny stems.
• RRV is systemic to the plant, but does not live in the soil.
• If the plant becomes systemically affected, it may die within a few years.
• Vines, ramblers, and well-pruned hybrid teas are less likely to be hosts.
• There is no cure at this time. Prevention efforts with an IPM (Integrated Pest Management) approach may reduce chances of getting the viral disease. IPM goal is to create an environment less prone to infection, and to target the vector, a wooly mite.
• The mite that transmits the disease can travel on the wind, for many miles. The mite is tiny and invisible to the human eye without magnification.
• Heavily pruned roses are less susceptible to the disease. A spray of horticultural oil in winter just before dormancy break may help slow the problem by knocking back some of the mite population.
• It is unclear if a repeat pesticide treatment during the growing season is effective. If you treat your roses in spring for Sawfly with a neem oil, it won’t hurt any other IPM efforts for RRV.
• Plant climbing roses or ramblers which seem to be less susceptible than shrub roses.
• Plant and prune so that plants do not touch each other, to avoid cross-contact
• Remove and destroy any infected rose. Don’t put this in the compost.
• http://www.ars.org/pdfs/rose_rosette.pdf
• http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-16.pdf
The good news is there are a lot of other beautiful plants we are growing that will give us flowers throughout the year. Plenty of hardy plants around that don’t play victim very often to pest problems: daisies, sunflowers, zinnias, the almost fool-proof butterfly bush, hostas, beautyberry, hardy azaleas, the ever-tough coreopsis, annual vinca, and so on.
Winter Garden To Do List:
Prune and thin boxwoods in February. There is more than one school of thought about boxwoods, so do some research. I go with thinning in the dormant season, to open up the interior for air flow, sunlight, and deadwood removal. This can be done with or without the ‘clouding’ effect.
Prune roses on a dry cool day in February .
Trim ornamental grasses including monkey grass. Do not trim sedges. For smaller grasses like Little Bluestem, Miscanthus, etc, I use hand pruners or ‘secateurs’ as they are known across the pond. For large grasses that are hard to handle like Switch grass I usually have a helper and gas powered hedge trimmers. Tie up the base of the plant, maybe 12-15 inches above the ground, with some compostable twine. Then have the very trusting helper hold the top so it doesn’t flop around. Carefully watching all things non-plant, announce that you are starting to cut, and then run the hedge trimmers smoothly through the grass stems. Rake up and compost the trimmings.
With all things involving cutting, use sharp tools, and clean the blades with alcohol between species or between any individuals suspected of disease.
Plant winter vegetables including greens, onions, beets. I wait until February to start my beets and onions. But greens –collards, kale, spinach – are pretty cheap as seed and you can start planting a series of rows, every couple of weeks until really warm weather.
