Black Eyed Susans dying - Ask Extension
My neighbor gave me black eyed Susans a couple years ago and I planted them around my redbud street trees. I noticed this summer that some of them se...
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Black Eyed Susans dying #888179
Asked October 17, 2024, 3:24 PM EDT
My neighbor gave me black eyed Susans a couple years ago and I planted them around my redbud street trees. I noticed this summer that some of them seemed to suddenly die. When I pull them up some of them have mycelia on the roots so I thought Southern blight might be the problem. But only once have I noticed something that looks like sclerotia. Many of them break off above the roots. I decided to dig up the top few inches of soil, but realized this is impractical. The trash bag was too heavy to pick up after a small corner of the bed! Plus I don't want to hurt the redbuds. I think it's too shady to solarize. Is it southern blight? Or just the regular short life cycle of Black Eyed Susans? What should I do? I included a picture of the only sclerotia I could find today. I transplanted some this spring. They don't seem affected.
Baltimore County Maryland
Expert Response
It's hard to tell what caused the dieback, and while Southern Blight is a possibility back during the summer months (as it's not a disease of cooler weather), we can't say if that was the only cause (or present at all, since other fungal blights can also kill stems). That pathogen is very common in the environment, and can't be practically eradicated, though it isn't always a recurring problem. Some species of Black-eyed Susan, of which there are several that look very similar to each other, have shorter natural life spans than others. Depending on what variety/species/subspecies you were given, that might be a factor as well. In that case, allowing them to reseed will help to perpetuate the planting for the long term.
Were the plantings watered periodically during the summer drought? If not, drought stress might be a contributing factor.
There isn't much that can be done about pathogens like Southern Blight and similar diseases. Reducing plant crowding and reducing mulch depth can help by improving airflow within/around plants, but it's not a foolproof solution. While drenching the soil during the growing season with a fungicide (labeled for this or other soil-borne pathogens) might help to reduce the risk of infection, its use also comes with a risk to other organisms, as some fungicide ingredients have been known to affect the health of bees, and may also harm beneficial microbes. For native plant gardens and plants with pollinator appeal like Black-eyed Susans, this would understandably not be a risk worth taking. Plus, it's not guaranteed to work. If the issue persists, adding other species to the planting instead of replanting any lost Black-eyed Susans can help to diversify the area so that any future blight or pest/disease outbreak is less likely to cause as much damage to all plants equally as it might in a single-species planting. (You might already have done this, but we mention it in case it's useful.) To be fair, Southern Blight can affect hundreds of species, so we don't have a resistant plant list to reference, but at least it does not kill roots directly, and affected plants may have the potential to regrow if their roots are otherwise healthy and have enough stored energy to do so.
Miri
Were the plantings watered periodically during the summer drought? If not, drought stress might be a contributing factor.
There isn't much that can be done about pathogens like Southern Blight and similar diseases. Reducing plant crowding and reducing mulch depth can help by improving airflow within/around plants, but it's not a foolproof solution. While drenching the soil during the growing season with a fungicide (labeled for this or other soil-borne pathogens) might help to reduce the risk of infection, its use also comes with a risk to other organisms, as some fungicide ingredients have been known to affect the health of bees, and may also harm beneficial microbes. For native plant gardens and plants with pollinator appeal like Black-eyed Susans, this would understandably not be a risk worth taking. Plus, it's not guaranteed to work. If the issue persists, adding other species to the planting instead of replanting any lost Black-eyed Susans can help to diversify the area so that any future blight or pest/disease outbreak is less likely to cause as much damage to all plants equally as it might in a single-species planting. (You might already have done this, but we mention it in case it's useful.) To be fair, Southern Blight can affect hundreds of species, so we don't have a resistant plant list to reference, but at least it does not kill roots directly, and affected plants may have the potential to regrow if their roots are otherwise healthy and have enough stored energy to do so.
Miri
