Limelight hydrangea problem... viral disease? - Ask Extension
In the 2021 season, nearly all of our years-old limelight hydrangea plants failed to blossom and instead showed an abnormal bloom as shown in the atta...
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Limelight hydrangea problem... viral disease? #802767
Asked July 24, 2022, 4:00 PM EDT
In the 2021 season, nearly all of our years-old limelight hydrangea plants failed to blossom and instead showed an abnormal bloom as shown in the attached pictures. We uprooted and disposed of the affected plants. This year, the remaining hydrangeas are similarly affected. The pictures are from one plant taken today. New hydrangeas planted last fall are blooming nicely now, right next to the affected ones. Foliage on the affected plants looks rigorous and healthy, other than the blooms. No evidence of insect damage or fungal/bacterial infection. Could this be viral? Thanks, any help is appreciated. Our local garden centers are stumped.
Montgomery County Maryland
Expert Response
Adding a couple more pictures...
Although plant viruses are numerous and regularly being discovered, not all cause significant plant damage or mortality. Still, one Tennessee State publication on hydrangea diseases mentions that fifteen different viruses have been reported in hydrangea. However, similar symptoms of distortion and stunting in shrubs are usually caused by exposure to an herbicide. Several types of herbicides mimic plant growth hormone activity in order to kill weeds by interfering with normal growth and blooming, and they will cause the same damage on desirable plants receiving a lower dose via airborne drift onto foliage or runoff into the root zone.
Some plant species or cultivars are more sensitive to herbicide exposure than others, and while we do not have data specific to hydrangeas, anecdotally we have seen several examples of mature hydrangeas manifesting damage. Some herbicide formulations are more likely to volatilize (evaporate into a vapor) or move in surface water than others, which is one reason they should not be applied on warm or breezy days or just prior to rain. (Details about weather restrictions will be mentioned in the product label.)
If you did not use any type of herbicide, perhaps an upwind neighbor or farm did within a few days or weeks prior to the onset of symptoms. How long these chemicals persist in the environment also depends on their formulation; some biodegrade relatively rapidly upon exposure to soil microbes, sunlight, and other elements.
Lastly, if herbicide use by anyone nearby seems unlikely, this could indeed be viral or a case of Aster Yellows. (That disease is not caused by a virus, but since the pathogen behaves similarly, they tend to be lumped together.) The most common landscape plant which contracts overt Aster Yellows symptoms are coneflowers (Echinacea), though the pathogen's potential host range is fairly broad overall. Testing for viruses is generally not practical in terms of cost-effectiveness since lab tests can be hard to source and are expensive; viral diseases are incurable and the affected plants must be removed. Insects feeding on plant juices/sap tend to be the vectors that move viruses from plant to plant, though gardening tools might play a role, via contaminated sap on the metal that is hard to clean off and sanitize. Shrubs suffering from herbicide exposure may or may not be able to outgrow the damage; time will tell if they can produce normal-looking regrowth, especially if the deformed areas are trimmed out.
Miri
Some plant species or cultivars are more sensitive to herbicide exposure than others, and while we do not have data specific to hydrangeas, anecdotally we have seen several examples of mature hydrangeas manifesting damage. Some herbicide formulations are more likely to volatilize (evaporate into a vapor) or move in surface water than others, which is one reason they should not be applied on warm or breezy days or just prior to rain. (Details about weather restrictions will be mentioned in the product label.)
If you did not use any type of herbicide, perhaps an upwind neighbor or farm did within a few days or weeks prior to the onset of symptoms. How long these chemicals persist in the environment also depends on their formulation; some biodegrade relatively rapidly upon exposure to soil microbes, sunlight, and other elements.
Lastly, if herbicide use by anyone nearby seems unlikely, this could indeed be viral or a case of Aster Yellows. (That disease is not caused by a virus, but since the pathogen behaves similarly, they tend to be lumped together.) The most common landscape plant which contracts overt Aster Yellows symptoms are coneflowers (Echinacea), though the pathogen's potential host range is fairly broad overall. Testing for viruses is generally not practical in terms of cost-effectiveness since lab tests can be hard to source and are expensive; viral diseases are incurable and the affected plants must be removed. Insects feeding on plant juices/sap tend to be the vectors that move viruses from plant to plant, though gardening tools might play a role, via contaminated sap on the metal that is hard to clean off and sanitize. Shrubs suffering from herbicide exposure may or may not be able to outgrow the damage; time will tell if they can produce normal-looking regrowth, especially if the deformed areas are trimmed out.
Miri
