Preventing Black-Eyed Susan Rust and 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 black-eyed Susan 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 black-eyed Susans were plagued by rust, gray mold, and mildew. And it wasn't just our black-eyed Susan either. The clumps 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.
Basic Garden Maintenance
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. Some basic garden maintenance for your black-eyed Susan includes:
- keeping them well-spaced and weed free.
- planting them in an appropriate location.
- dividing them as often as necessary.
- cutting back the flower stalks.
- watering the plants from the bottom.
- removing any and all infected plant parts.
Have you, or are you, having mold and 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.
How To Prevent Rust, Mildew, and Fungus on Black-Eyed Susan
Avoid using harsh chemicals in your garden with these 7 tips.
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 and Cutting
Spacing Your Plants
Mature 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 the plants after their first blooming will also increase airflow—and your flowers will bloom again!
Formerly, I allowed our flowers to go to seed in the fall, thinking its dried stalks and flower heads 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 flowers back at least twice: once after the first flowering and once at the end of fall.
Dividing and 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 and Conquer (Fungus, That Is)
Black-eyed Susan 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 and Bugs
And keep the weeds down, too. Not only do they hold moisture, but they also attract pests. You don't need those, too!
Watering and 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.
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.
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.
Black-Eyed Susan Care Tips
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
Questions & Answers
All my black eyed Susan’s have this and all over. It’s now affecting other plants like my shasta daisies. My roses look awful too. What do I do? Remove them all but cutting everything off or digging them up?
You probably have more than one issue if all of these plants are having problems, especially the shasta daisies, which usually don't have severe fungal problems. I'm wondering if it isn't pest damage. Check out this extension webpage regarding the fourlined bug https://extension.umn.edu/yard-and-garden-insects/... They produce black spots on shastas. If you have fungal issues, too, you could try removing the black-eyed Susans and thinning the other plants so that there is lots of space around them. This would reduce the moisture that encourages fungal disease. Also, if you have a heavy application of mulch, scrape it back so there's only two inches at most. Pruning your roses, especially their centers, will help reduce trapped moisture also.Helpful 16
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 9
My black-eyed Susans are very small but popping out and already have black spots. Is something wrong?
If some of the plants already are showing signs of rust, I would dig the rusty plants up and discard them (don't compost them) then scrape away and discard as much of the mulch or soil around them as well to mitigate (not necessarily eliminate) the problem. Your remaining plants may develop some rust anyway, but if you're like me, you may not mind a little damage, right? After all, your plants are real ones, not plastic.Helpful 6
My plants are turning crispy brown in the middle of the clump. What could cause this?
It sounds as if some sort of pathogen is at play, perhaps Sclerotinia Sclerotiorum and Sclerotium Rolfsii. I would dig out the affected part and throw it away then diligently deadhead and water in a manner that does not wet the leaves.Helpful 4
© 2013 Jill Spencer