Dahlias are dying

Mentor, OH

What started off as a pretty good year for dahlias has gone south the last couple weeks. The problem is only in one bed where the leaves are turning brown and the stems feel like wet noodles. I dug up a few tubers and some look perfectly fine while others were in various stages of rot. I'm sure it's not from over-watering since plants in two nearby beds are thriving and blooming their heads off. They also get the same amount of sun. The dying has gone from right to left taking each plant as it goes. Therefore, I think it has to be caused by some virus. Luckily, every plant in this bed was a mis-labeled that I was discarding this Fall anyway. Friends and neighbors have asked for the tubers but since I'm afraid they're diseased, the only person getting them will be the garbage collector. This is the same bed that I posted about in July that was getting eaten by Asiatic beetles. Is it possible that the beetles combined with the super hot, dry weather caused a stressful condition that the plants could not overcome? This is only my second year with dahlias,so any comments would be greatly appreciated. This plant pictured had big, beautiful purple flowers two weeks ago.

Thumbnail by psudan
Mentor, OH

This one died a few days ago. Last week it was covered with red flowers.

Thumbnail by psudan
(Pony) Lakewood, WA(Zone 8a)

Yikes. I have no idea. I hope some of the experienced folks here can tell you what caused that!

If I see any signs of a problem on my plants, I spray the heck out of them with neem. It fixes things most of the time, since it works on pests and fungus, etc. it's kind of a cure-all.

(Arlene) Southold, NY(Zone 7a)

Dan - sorry to see those photos and hear of what happened with your dahlias. I also have no idea what could have caused it but stress sounds like a probable cause. Is the soil similar in all areas or could the dying ones have been in more clay?

I'd be cautious about planting again in the soil but winter may kill any virus now present.

Would you consider calling your local Cooperative Extension Service and asking them?

Mentor, OH

Pirl, all three areas have very similar soil. This particular area may have slightly more sand but not much difference. I went to our local Extension Service recently when my tomatoes had blossom end rot. They were extremely helpful and knowledgeable and from what I understand very under-utilized by local gardeners. I will go there as soon as I have a chance. Thanks for your response.

(Arlene) Southold, NY(Zone 7a)

Good luck, Dan. Some Extension Services are better than others so I'm glad you have a good one.

In the meantime would you consider just cutting back each dahlia, removing all brown leaves/stems/flowers, and seeing if they perk up again?

Ft Lauderdale, FL(Zone 10a)

I'm thinking its something bacterial like grey mold/powdery mildew or downey mildew. That would also explain why it's hopping from plant to plant in the infected area. These bacterial infections are also most common in late summer....I believe. If it is one of these three bacterial issues, the plants look too infected to begin treatment with a fungicide or pesticide. Perhaps pirl's suggestion to just cut the plant back down to ground level would be the best option. That would also reduce the risk that the bacterial issue could spread to one of the other flower beds.


(Arlene) Southold, NY(Zone 7a)

Good thought about the fungus and spreading it.

Don't put the pieces you cut off into your own compost. It's not worth the risk of spreading a problem.

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