Preventing Black-Eyed Susan Rust & Fungus Naturally
With their brown button centers and bright yellow petals, Rudbeckia hirta flowers (commonly called black-eyed Susan) are cheery additions to informal gardens, landscaping islands, mailbox gardens and borders. To me, they're a cottage garden staple and an absolute must-have for gardeners in Maryland, where Rudbeckia hirta is the state flower.
Formerly, I grew them with blithe ease—planting them in various spots in our landscape, watering them occasionally during the hottest days of summer and dividing the thick green bunches every few years in either the spring or fall.
Until two years ago, when our lovely clumps of Rudbeckia hirta were plagued by rust, gray mold and mildew. And it wasn't just our black-eyed Susan either.The clumps of Rudbeckia hirta in our neighbors' yards and in the parks and public gardens where I volunteer were also suffering from rusty leaf spots and shriveled stalks that looked almost burnt at the bottoms.
Fortunately, our plants didn't die from their infections, but they looked like they wanted to! What to do—without resorting to chemicals (which I adamantly refuse to use)?
What I SHOULD Have Been Doing
After researching the problem, I discovered that I should start doing what I should have been doing all along: caring for my Rudbeckia hirta in a less cavalier fashion by
- keeping them well-spaced & weed free,
- planting them in an appropriate location,
- dividing them as often as necessary (not as often as was convenient),
- cutting back the flower stalks,
- watering the plants from the bottom &
- removing any & all infected plant parts—
in other words, basic garden maintenance.
Have you or are you having mold & mildew issues in your garden?
Of course, if I had done these things previously, our black-eyed Susan might still have become infected. In fact, it probably would have. After all, Rudbeckia hirta is naturally prone to rust, gray mold and mildew infections.
But I don't think it would have succumbed so completely, especially since our plants are doing fairly well now that I'm treating them with the care that they deserve.
7 Ways to Prevent Rust, Mildew & Fungus on Black-eyed Susan (that don't involve chemicals)
These methods for preventing mildew, gray mold and rust on Rudbeckia hirta plants are aimed at keeping moisture around the plant down (mold, fungi and rust love moisture) and lessening the spread of the spores that cause infections.
Spacing & Cutting
Spacing Black-eyed Susan
Mature Rudbeckia hirta plants usually have a spread of one to two feet, so remember that when you're planting, especially if you're doing a mass planting.
You want there to be enough room around each plant so that air can circulate. Good air flow will reduce the likelihood of the sort of moisture build-up that encourages mold and mildew.
Cutting Back Black-eyed Susan
Cutting back the plants after their first blooming will also increase air flow—and your flowers will bloom again!
Formerly, I allowed our Rudbeckia hirta to go to seed in the fall, thinking its dried stalks and flowerheads would lend structure to our garden and that the seeds would feed the birds.
Now, although I liked the look and the birds liked the seed, I realize that not cutting the plants back at the end of the growing season was a mistake. During the freezes and thaws of winter, moisture collected in the plants, providing the perfect environment for mold and mildew. And almost as soon as the plants emerged in spring, we began having rust, mold and mildew problems.
So these days, I cut our Rudbeckia hirta back at least twice: once after the first flowering and once at the end of fall.
Dividing & Weeding
Regularly dividing Rudbeckia hirta means you're going to have lots of little black-eyed Susan plants!
You could always plant them elsewhere in your garden. You could also give the extras to friends, donate them to parks, or compost them (if they're disease free.)
Divide & Conquer (Fungus, That Is)
Rudbeckia hirta has a tendency to spread, particularly when it's in the sort of location it likes: full-sun and rich, well-drained soil. When it spreads, however, it creates masses of close clumps, and you know what that means! Moisture and, ultimately, rust and mold.
To prevent this, you can do one of two things. Either divide your plants in the spring or fall (spring's best) when they've formed a mass of too-tight clumps. (In our case, that means yearly.) Or, periodically remove the small plants that form from rhizomes next to the main clump.
Weeds = Moisture & Bugs
And keep the weeds down, too. Not only do they hold moisture, they attract pests. And you don't need those, too!
Watering & Placement
Watering Black-eyed Susan
I know it's much easier to spray your entire flowerbed with a hose than it is to water each individual plant at its base, but overhead watering almost guarantees rust and mildew on black-eyed Susan.
Of course, you could use an old galvanized can and water from the rain barrel if you want to make the whole process as back-breaking as possible. (That's what I do. You should see my muscles!) But a soaker hose attached to a spigot or rain barrel, or an in-ground watering system can make the task of watering your Rudbeckia hirta from the bottom as simple as turning a spigot.
Picking a Good Location
Overwatering will cause rust and mildew, too, as will positioning your black-eyed Susan in a shady rather than a full-sun spot or planting it in soil that doesn't drain well.
I now water our black-eyed Susan sparingly, only on the hottest days and always in the morning.
In order to lessen the spread of infection, be sure to clean the blades of any garden tools that you use to remove infected plant parts before you use them elsewhere in the garden. Rubbing alcohol works well for this.
Removing Infected Foliage
If, despite your best efforts, the Rudbeckia hirta in your garden becomes infected with rust, mold or mildew, remove infected stems and leaves, both from the plant and the ground. Then bag them up and stick them in the trash posthaste.
Because of our past problems with disease, I inspect our clumps of black-eyed Susan regularly, immediately removing any withered leaves on the ground and snipping off any leaves that look infected.
Because fungal spores can live on infected leaves, in mulch and in the ground for a long time, it's a good idea to scrape up debris from around infected plants, bag it and dispose of it, too—you know, just in case.
Basic Rudbeckia hirta Care Tips
About the Author
The Dirt Farmer has been an active gardener for over 30 years.
She first began gardening as a child alongside her grandfather on her parents' farm.
Today, The Dirt Farmer gardens at home, volunteers at community gardens and continues to learn about gardening through the MD Master Gardener program.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
I have often heard that a horticulturist favorite is using a mix of milk and water, ratio 3/1, can combat fungal disease. Will this helps me with rudbekia?
A milk/water fungicide has shown some effect on powdery mildew. That may be helpful, depending upon what fungus your rudbeckia has. There are several that infect rudbeckia.
This concoction is usually only used on vegetable gardens because it has an unpleasant odor.Helpful 7
© 2013 Jill Spencer