Possible Aster Yellows infection - Ask Extension
How does one confirm an aster yellows infection? What if the plants lack nutrients or have an insect or fungal infection? I hesitate to destroy so man...
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Possible Aster Yellows infection #874676
Asked June 25, 2024, 4:48 PM EDT
How does one confirm an aster yellows infection? What if the plants lack nutrients or have an insect or fungal infection? I hesitate to destroy so many plants that could be saved with the right diagnosis and treatment. The following are pictures taken today, June 25. The conditions in Maryland have been hot, with highs between 86 and 101 over the last 10 days. I don't think my soil is in great condition. I moved hardwood mulch away for the pictures so that the stems could be visible. I sprayed them with neem oil about 14 days ago because I thought maybe they had a little something going on, but it didn't seem like something to be overly concerned about at that time. Up until about a week ago all of my plants seemed pretty happy and healthy. I am flummoxed and, honestly, kinda sad that I may have to destroy so many of my plants. I Please, help me identify the problem and advise me what I should do. Thank you so much.
Howard County Maryland
Expert Response
Fortunately, none of the plants pictured have symptoms of Aster Yellows disease, which look very different and distinctive. (Examples focusing on Coneflower symptoms are in the linked page.) The Zinnia foliage pictured is showing typical, though minor, infection from either fungal or bacterial infection. (Its appearance suggests it is fungal in this case.)
No treatment is needed, but only certain fungicides might suppress its spread. Since fungicides can potentially harm other organisms, however (including bees or other pollinators drawn to these flowers), and because they cannot cure existing disease, we do not recommend their use in this situation. Cut flower growers who encounter this type of leaf damage on their Zinnias usually do not treat the plants, since the flower quality isn't seriously impacted. Since the lowermost leaves on the stem tend to be infected first, snip them off and dispose of them if they become symptomatic. Monitor the plants for watering needs as well, since leaf scorch from getting too dry or staying too wet (if watered too often) can also cause leaf edges to brown or leaves to become yellower. Try to only wet the soil when watering, rather than sprinkling the whole plant, since wet foliage can easier for disease spores to infect. If wetting the foliage is unavoidable, then water early in the day so the leaves can dry off by nightfall.
In recent weeks, Maryland weather has turned abnormally dry, and we are approaching drought if the rain shortage continues. (Drought took place last summer as well.) If you think they aren't getting enough water, or if you're uncertain when to water, feel the soil by the plant's roots around four inches deep. If somewhat dry to the touch at that depth, water thoroughly. If damp when checked, watering can probably wait. If you think the soil is poor in terms of compaction and moisture retention, adding compost and mixing it in next season can help. For the time being, top-dressing with up to an inch of compost might help a little, though it would be more beneficial used from the start of the season to avoid disturbing the plant roots.
The Dahlia foliage looks minimally affected by fungal infection as well, plus what looks like minor slug/snail feeding, so just trim any unsightly leaves off. There is a small amount of stippling, which is the result of sap-sucking insect feeding, potentially from leafhoppers in this case. No treatment is needed for them either.
The Marigold foliage looks afflicted with moderate levels of spider mite feeding, which is very common for that plant since that's a pest they are particularly vulnerable to. Hose the leaf undersides off to remove most of the mites, and if needed, trim the worst of the leaves being yellowed off.
Miri
No treatment is needed, but only certain fungicides might suppress its spread. Since fungicides can potentially harm other organisms, however (including bees or other pollinators drawn to these flowers), and because they cannot cure existing disease, we do not recommend their use in this situation. Cut flower growers who encounter this type of leaf damage on their Zinnias usually do not treat the plants, since the flower quality isn't seriously impacted. Since the lowermost leaves on the stem tend to be infected first, snip them off and dispose of them if they become symptomatic. Monitor the plants for watering needs as well, since leaf scorch from getting too dry or staying too wet (if watered too often) can also cause leaf edges to brown or leaves to become yellower. Try to only wet the soil when watering, rather than sprinkling the whole plant, since wet foliage can easier for disease spores to infect. If wetting the foliage is unavoidable, then water early in the day so the leaves can dry off by nightfall.
In recent weeks, Maryland weather has turned abnormally dry, and we are approaching drought if the rain shortage continues. (Drought took place last summer as well.) If you think they aren't getting enough water, or if you're uncertain when to water, feel the soil by the plant's roots around four inches deep. If somewhat dry to the touch at that depth, water thoroughly. If damp when checked, watering can probably wait. If you think the soil is poor in terms of compaction and moisture retention, adding compost and mixing it in next season can help. For the time being, top-dressing with up to an inch of compost might help a little, though it would be more beneficial used from the start of the season to avoid disturbing the plant roots.
The Dahlia foliage looks minimally affected by fungal infection as well, plus what looks like minor slug/snail feeding, so just trim any unsightly leaves off. There is a small amount of stippling, which is the result of sap-sucking insect feeding, potentially from leafhoppers in this case. No treatment is needed for them either.
The Marigold foliage looks afflicted with moderate levels of spider mite feeding, which is very common for that plant since that's a pest they are particularly vulnerable to. Hose the leaf undersides off to remove most of the mites, and if needed, trim the worst of the leaves being yellowed off.
Miri
