The best way to keep disease out of your winter annual flower beds is to start with disease resistant plants.
Take another blooming plant, crape myrtle for instance. Selecting powdery mildew resistant cultivars is easy. You just buy the ones with the Indian names. Some of them include the white flowering Natchez’ and the lavender flowering Muskogee. But selecting disease resistant flowering annuals takes a little more research.
When you add pansies to your winter landscape, select from this list of leaf spot resistant varieties: Bingo Red & Yellow, Crown Golden, Crystal Bowl Supreme Yellow, Crystal Bowl True Blue, Dynamite Red & Yellow, Majestic Giants Yellow and Viola Sorbet Blackberry Cream.
Leaf spot resistance doesn’t mean they are totally immune to disease, it just means they get less disease than susceptible varieties.
If Patiola pansies are your flowers of choice, buy Purple Passion Mix, Pure Yellow, Pure Lemon, and Pure Orange. These varieties are less susceptible to Cercospora leaf spot than the Colossus series cultivars.
This winter we might see snapdragons and pansies with powdery mildew. This disease likes wet, humid and cooler weather. We’ve certainly had a lot of that since the first of December.
The best control method is to remove the downy mildew infected plants because it spreads very fast. And once it gets in the bed, you won’t be able to control it. For some reason, people have a hard time pulling up diseased plants in their beds. I guess they just don’t want to throw something away, but you are much better off doing that than have the disease spread and wipe out all your plants.
Impatiens, another one of our favorite summer annual flowers, first got infected with downy mildew during the summer of 2012. If a bed of these flowers had downy mildew, more than likely they will get it again if you plant them in the same spot.
It can be hard to spot the symptoms initially, but what follows is, subtle leaf discoloration, downward cupping of leaves, white sporulation on the leaf underside, then rapid defoliation. Eventually your impatiens with look like bare stems or twigs.
Surprisingly downy mildew was not that big of a problem last year, unlike the year before, but we never know what to expect from year to year.
Root rot disease is also a major problem in winter landscape beds. Overall, we have had a pretty wet winter, which makes conditions ideal for root rot diseases. This problem is compounded by people who don’t cut their sprinkler systems off during the winter.
You also make problems worse by bringing home cheap or almost dead plants that are on sale.
To help prevent root rot diseases, install plants in a raised bed, don’t plant too deeply, improving soil drainage, and redirect water so plants are not overwatered. Also, don’t till in old plants and plant material. If you had disease there before, you are just incorporating that material back in the area.
Because root rot diseases thrive in moisture, inspect plant beds and make sure there are no sources of extra water, such as a downspout aimed into a bed or an irrigation pattern that directly hits the area.
Another root rot, called black root rot, produces black spores in chains that survive in the soil. In large numbers, they cause the roots to look black, thus the name. The disease favors cooler temperatures and alkaline soils so soil test your beds every few years to make sure the pH stays below 5.8.
Avoiding susceptible plants will also help fight black root rot. Susceptible plants include vincas, pansies/violas snapdragons, impatiens, petunias, calibrachoas, verbenas and begonias. Less susceptible plants are salvias, geraniums, marigolds, zinnias, dusty millers, coleuses, and celosias.
One final thing – wash your tools to keep them clean and to reduce the chance of infection.
REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.