Dahlia - bugs or disease?

Hi all! One of my new dahlia - started from tuber in greenhouse - has serious issues. See pic. I cannot find anything that looks like it online. If it's bugs, I'll try to save it. If it's virus or fungus, I'll send it to the tip... No other plants in greenhouse have this problem. It has been isolated and outside greenhouse for a couple of weeks now. Not dead but certainly unhappy. I sprayed with dilute fairy liquid about a week ago which was when all the little brown circles showed up. Prior to that just leaves at bottom looked damaged. Anybody know what's wrong with it please?

 

Hi,

If it was in the greenhouse a very common pest is Red Spider Mite, which a suitable spray should eliminate, plus putting it outside would also help.
You need a strong magnifier to see them, unless they are a big infectation then you can see a web like a small normal spider.

Sounds more like your soapy water has been applied during strong sun and its cause the leaves to burn like that ?

Any damaged leaves are unliked to recover but if it puts out new green shoots then it may be worth saving and planting out, or take those new shoots as cuttings and start some new plants.

 

Thank you and other commenters! My soapy mix may well have been too strong, as I was fighting a horrible infestation of black fly on my broad beans and made a vat in a hurry without measuring it. Many broad bean leaves also went brown, but plants are not infested any more and have new top growth. I wonder if the soap penetrates damaged areas of plant actually. Or soap on damaged areas kills that bit of leaf. Certainly the brown is where the aphids were and not other places on the BB. Not sure if it was sunny or not - dahlia has been at side of shed, but it does catch sun in morning I think. Was def sunny when sprayed BB.... I was in a hurry :(
I have hope again now anyway. I recently bought some NEEM oil and an emulsifier to make a spray. Never used before, but might try it. Anybody use it?

 

Thank you, this was useful. Seems like it might work on mites or most other things for that matter!

 

We usually have a small bed of Dahlias which at some point get BlackFly which we used to use a spray, but last year we just left them and let nature do its work.
We lost a few shoots to them but the ladybirds and other creature actually clean them off, and within a coupe of weeks it all looked good again.

As a non toxic treatment you could try a weekly spray of SB Invigorator,