Preventing Black-Eyed Susan Rust and Fungus Naturally

Updated on May 5, 2019
The Dirt Farmer profile image

Jill likes cooking, writing, painting, & stewardship, and studies gardening through MD Master Gardener & Master Naturalist programs.


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.

Simple, right?

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.

An overcrowded patch of black-eyed Susan in a shady spot equals a hotbed of rust. Ew!
An overcrowded patch of black-eyed Susan in a shady spot equals a hotbed of rust. Ew! | Source

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.

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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.

Who doesn't love the cheery faces of Rudbeckia hirta flowers? They're adorable!
Who doesn't love the cheery faces of Rudbeckia hirta flowers? They're adorable! | Source

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.

Rudbeckia hirta generally grows in clumps anywhere from one to two feet wide.
Rudbeckia hirta generally grows in clumps anywhere from one to two feet wide. | Source

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

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

Although thick masses of black-eyed Susan in the shade are pretty at first, the size and location are an invitation to disease. Pictured: our Rudbeckia hirta before being hit by a nasty bout of rust.
Although thick masses of black-eyed Susan in the shade are pretty at first, the size and location are an invitation to disease. Pictured: our Rudbeckia hirta before being hit by a nasty bout of rust. | Source

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!

Removing new plants that form from rhizomes at the base of clumps will keep moisture down by improving air flow. And if they're rusty, as these are, you'll definitely want to remove them posthaste!
Removing new plants that form from rhizomes at the base of clumps will keep moisture down by improving air flow. And if they're rusty, as these are, you'll definitely want to remove them posthaste! | Source

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 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.

  • 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.

  • 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.

  • 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.

© 2013 Jill Spencer


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    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      2 months ago from United States

      Hi, Pamela. Shriveling doesn't sound like rust. It could be a pest or Verticillium wilt. You might want to dig up the shriveling plants, remove the damaged parts, shake off the old dirt, wash the plants with insecticidal soap, and plant them in a pot or pots with new soil. This would take care of the problem if it's a pest. If it's wilt, getting the plants out of the ground and into a pot with soil that drains well would help. If your plants are in a wet area, that exacerbates wilt. Whether you decide to leave the plants where they are or pot them, be sure to remove the infected parts and destroy (don't compost) them. Good luck to you!

    • profile image


      2 months ago

      My black eyed Susan’s are not in bloom yet but some of the new leaves are shriveled and there is sometime inside that is black kind of grainy about the size of a pea. The leaf has indications of damage with brown areas. What is it and can I get rid of it or do I just have to dig up all my plants that are infected.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      5 years ago from United States

      Hi Sherry! Thanks for stopping by and taking the time to comment. Thanks for the votes, too! All the best, Jill

    • tricomanagement profile image


      5 years ago

      voted up across the board - as always thanks for good information and well written


    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi Glimmer Twin. Yes, it does sound like your daisies have fungus. Glad the hub is helpful to you & thanks for sharing it.

      Awesome, Peggy! Thanks for the vote & the pin.

      Ms. Dora, I hope the info helps you out w/the fungus in your garden. It takes time & patience to get rid of it, that's for sure. Take care, Jill

    • MsDora profile image

      Dora Weithers 

      7 years ago from The Caribbean

      Just the information I need about getting rid of fungus. Thanks so uch for sharing this information.

    • Peggy W profile image

      Peggy Woods 

      7 years ago from Houston, Texas

      These are some great tips. Unfortunately when we run our sprinkler system, everything gets watered from the top but other than that, the other methods you use can be utilized in our garden. Voted up and pinning.

    • Glimmer Twin Fan profile image

      Claudia Mitchell 

      7 years ago

      Well this could not have come at a better time. This look exactly like what is one of my sedums. My black eyed Susans are ok. I will be referencing this later today after these wicked storms have passed. One thing I noticed this spring is my shasta daisies all have white spots on them. I wonder if it's the same thing. The foliage looks paler this year too. I't probably time to divide them since I never have in the 5 years we have lived here. Shared all around.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi azrestoexp! Rudbeckia hirta should grow there. Try planting them in March, April, Oct. or Nov. if you are in Zone 10. (On my map it looks like you are.) Good luck! You shouldn't have fungus problems there. And once they're established, black-eyed Susan is fairly drought tolerant. Take care, Jill

    • azrestoexp profile image

      Arizona's Restoration Experts, LLC 

      7 years ago

      Nice hub. Voted up. I love the black-eyed Susan but don't think they grow in Phoenix. Would you know?

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi Deb. Black-eyed Susan are among my favorites, too. They're easy to grow, but as bitter experience has taught me, they can't be treated just anyhow! Thanks for commenting. Can't wait to see your next batch of pics from Boomer Lake. --Jill

    • aviannovice profile image

      Deb Hirt 

      7 years ago from Stillwater, OK

      I love these flowers. Thanks so much for the great gardening advice. It makes a lot of sense to know what one needs to do with these flowers.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi livingsta! Thanks for the share and the votes. Hope you have a wonderful week too. Jill

    • livingsta profile image


      7 years ago from United Kingdom

      This was a very useful and interesting read. The flowers look lovely. Thank you for sharing this information with us. Voted up, useful and interesting and sharing! Have a great week ahead!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi Barbara, I hope your black-eyed Susan don't get it, too. Once you do, it takes time and patience to get rid of it without using any sort of fungicide, organic or otherwise. I think many people don't realize that organic fungicides, herbicides and pesticides are harsh and, of course (or else they wouldn't work!) toxic even though they are organic. I try my best not to use anything other than best practices. Hope your garden stays healthy this year! --Jill

      Rebecca, you're going to have to get some black-eyed Susan, girl! (And keep up w/the neighbors.) (; Nice to hear from you--Jill

      Thanks for the votes & for sharing, Faith Reaper. Appreciate it!

    • Faith Reaper profile image

      Faith Reaper 

      7 years ago from southern USA

      Thanks for another useful and interesting hub here.

      Voted up ++ and sharing

      Blessings, Faith Reaper

    • rebeccamealey profile image

      Rebecca Mealey 

      7 years ago from Northeastern Georgia, USA

      I just love black-eyed susans. I don't have any of my own, but I enjoy them all around the neighborhood. This is good to know!

    • Barbara Kay profile image

      Barbara Badder 

      7 years ago from USA

      Here in Michigan, we are just starting summer. I hope we don't have the problem this year with ours.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi faythef. So sorry your black-eyed Susan are having problems. It's like an epidemic!

    • faythef profile image

      Faythe Payne 

      7 years ago from USA

      Thank you for the tips..Mine too are suffering from the same up and sharing.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 years ago from United States

      Hi Eddy! It's almost too hot here to go outside, but I'm going to anyway. Whew! Hope you enjoy your weekend, too. (: Jill

    • Eiddwen profile image


      7 years ago from Wales

      So interesting ;very useful and vote up.

      Have a great weekend.



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