Possible crown gall or other disease on scabiosa? - Ask Extension
Hello, I'm wondering what you think is on the bottom of this scabiosa/pincushion flower plant. It's about 2 years old now. Since it's cold hardy, it j...
Knowledgebase
Possible crown gall or other disease on scabiosa? #879202
Asked July 29, 2024, 10:19 AM EDT
Hello, I'm wondering what you think is on the bottom of this scabiosa/pincushion flower plant. It's about 2 years old now. Since it's cold hardy, it just happened to grow back this year and produced many beautiful blooms, most of which were all gone to seed by the time I saw this mass at the root system. Plants around it seem mostly ok, except the calendula (pictured), which always seem to get some sort of disease for me in this area anyway, so maybe they're the original culprit. I did plant a new dahlia tuber near this scabiosa but the dahlia plant seems ok, though not producing blooms yet. The soil is well-draining and pulse-watered. Thank you for any help!
Allegany County Maryland
Expert Response
We agree that the Scabiosa looks afflicted with Crown Gall, and as such, would need to be removed and disposed of since that infection is unfortunately not curable. These bacteria can be fairly ubiquitous in the soil, and tend to take advantage of plants that become injured, either through natural means (insect chewing, for example) or through human activities (transplanting, perhaps).
The symptoms pictured on the Calendula are unrelated, and could have been caused by spider mites, thrips, or another sap-sucking insect. Blasting the foliage a few times (perhaps 1-2 times per week) with a strong jet of plain water from a garden hose (let any hot water out first) might help to reduce a pest population, if it is still present at this point, without having to resort to insecticides. Spray the upper and lower leaf surfaces, since mites and thrips prefer to remain on the underside of the foliage. If needed, either insecticidal soap or horticultural oil might help to smother any remaining pests, though direct contact with the spray will be necessary for it to be effective, so sprays when the pest is not visible will not provide any benefit. If used, follow all product label directions, and do not apply while temperatures are above 85 degrees, or foliage tissue injury may result. Injured leaves cannot heal, so even if no treatment is needed because the pests have already finished feeding, or even if a treatment is working, the only indicator may be that new leaf growth remains damage-free.
Miri
The symptoms pictured on the Calendula are unrelated, and could have been caused by spider mites, thrips, or another sap-sucking insect. Blasting the foliage a few times (perhaps 1-2 times per week) with a strong jet of plain water from a garden hose (let any hot water out first) might help to reduce a pest population, if it is still present at this point, without having to resort to insecticides. Spray the upper and lower leaf surfaces, since mites and thrips prefer to remain on the underside of the foliage. If needed, either insecticidal soap or horticultural oil might help to smother any remaining pests, though direct contact with the spray will be necessary for it to be effective, so sprays when the pest is not visible will not provide any benefit. If used, follow all product label directions, and do not apply while temperatures are above 85 degrees, or foliage tissue injury may result. Injured leaves cannot heal, so even if no treatment is needed because the pests have already finished feeding, or even if a treatment is working, the only indicator may be that new leaf growth remains damage-free.
Miri
Thank you for this information, Miri; it's very helpful. As far as crown gall goes, once I remove the infected plant, is there anything I can do to ensure that future plants planted in that area don't also become infected since the bacteria live in the soil?
Lauren
You're welcome!
No, nothing you can do, really, aside from trying to avoid injuring a plant when planting or transplanting it. (Granted, minor injuries to roots and stems happen all the time in this process, and infections don't necessarily result the majority of the time.)
Miri
No, nothing you can do, really, aside from trying to avoid injuring a plant when planting or transplanting it. (Granted, minor injuries to roots and stems happen all the time in this process, and infections don't necessarily result the majority of the time.)
Miri
