Be vigilant to kill fungal disease that attacks snapdragons
Question: I have snapdragons that were blooming so well this season, but then they all dried up and looked terrible. I tried to cut them back but I think they all died. Usually I have these blooming until it's snowing. What do you think is wrong with my garden? The other flowers are doing OK.
Answer: Snapdragons (Antirrhinum majus) are short-lived, tender perennials that do quite well in our western Pennsylvania climate. Though they don't often overwinter, especially if it's particularly cold, occasionally snapdragon plants will survive the winter and return from their roots the following spring. They are fairly cold-tolerant and can be in bloom from spring until early winter. Protected sites sheltered from cold winds afford the best chance of overwintering this beautiful plant.
But, even if the plants themselves don't overwinter, their seeds often do. Snapdragons can return to a garden area year after year, if the mother plants are allowed to drop seed at the end of the growing season. And they do it with very little help from the resident gardener. I have several snapdragon varieties that return to my own garden every year via dropped seeds, and I don't do a thing to promote their efforts.
All that being said, despite the tough nature of snapdragons, there is an issue that can negatively influence their health and productivity, and I suspect this pathogen has struck your garden.
Snapdragon rust (Puccinia antirrhini) is a common fungal disease that affects only snapdragons and a few close relatives. Though this pathogen is very common on snapdragons, it doesn't necessarily result in death. But when the infection is severe, as I suspect yours was, the leaves and stems may shrivel, brown and die completely.
Like other fungal diseases, snapdragon rust is always more prevalent when the weather is wet, and our cool, wet spring and early summer was the perfect recipe for infection. The spores of snapdragon rust are spread primarily by wind, but also by water and insects, making it very easy for the pathogen to move from one plant to the next in short order.
Early symptoms include pale yellow spots on the upper leaf surface. When the leaves are flipped over, you'll see small, dark brown, orange or dusty gray pustules on the lower leaf surface. Once the infection has really set in, the leaves may turn brown and then fall off.
Spores of snapdragon rust easily overwinter in the garden, so it's imperative that you cut down and remove all snapdragon foliage from your garden at the end of the growing season. There's nothing you can add to the soil to eliminate the pathogen, so removing fallen foliage is essential.
After cutting back and cleaning up your diseased snapdragons or anytime you prune a diseased plant, disinfect your clippers with a disinfectant spray such as Lysol or a dip in a 10 percent bleach solution to keep the spores from spreading via infected equipment.
Often snapdragon rust returns in subsequent seasons only when there are cool, wet weather conditions. Just because it was problematic this year does not mean it will return next year, especially if you do a good job of cleaning up any remaining diseased foliage. Also, when you water snapdragons, do your best to water only the root zone and try to keep the foliage as dry as possible. A good layer of mulch, applied next spring, can also keep spores from splashing up out of the soil and onto the leaves.
Snapdragon rust is not known to be carried in the seeds, so starting new plants from seeds every year is another way to help stave off infections. Also, give each plant plenty of room to grow. This improved air circulation can reduce the rate of infection and keep it from spreading, should it happen to take hold.
And lastly, organic fungicides are another option for controlling snapdragon rust, but they're best used as a preventative or very soon after signs of infection are noted. Biological fungicides based on Bacillus subtilis (brand name Serenade) and those using copper as an active ingredient are effective, though great care should be taken to not use them when pollinators are active.
The “Coronette” and “Tahiti” series of snapdragons are said to be more rust resistant than other varieties, if you can find them on the market next spring.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.
Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.