Dahlia problem

Hi folks, I have a few Dahlias in my greenhouse which I started off a couple of weeks ago..a few have sprouted and were looking good until this week. They now have distorted growth and a whitish deposit on them. Any ideas?? They are 2 different varieties and one seems more prone than the other. Please help!! The greenhouse is unheated so gets v. hot during the day yet quite cold at night.
P.S. I planted some Bishop of Llandaff tubers at the same time and nothing.....any clues?

Thanks

Fletch

 

Hi Fletch

Oh dear, I've got loads of dahlias but haven't come across that problem before. Some of mine are in the (unheated) greenhouse and some were left in the ground over winter. None of them are sprouting yet. However, I'm sure someone will be along to help soon.

 

Hi fletch, can you describe these "whitish deposits" a bit more?where are they? are they raised or sunken? that sort of thing. David.

 

Hi David, they are all over the new leaves. They look like the kind of deposit you get from hard water, but the water here is very soft. They are on all the emerging new leaves. All the growth on all the dahlias has a very "yellowy" look to it, regardless of variety, not nice and green and healthy.
I don't know what I'm doing wrong, I've grown dahlias before, but always in a warm place in the house, never in a greenhouse, maybe it's the heat?????

Fletch

 

hi fletch this is my first year with dahlias i started mine of in the greenhouse but some one told me to put them outside i did and thy are doing all right Bean out now for about 3 weeks thy are in the sun in the morning and shad later on don't no if doing right or wrong but thy are up about 4in hope this helps

 

It sounds like powdery mildew - but I don't know if dahlias are prone to it. I'll have a google to see.

edit -
Apparently they do get it.... have a look here for info about it

 

I've been out in the greenhouse today and they are growing well but the growth is SO yellow. Maybe I've got some duff tubers?
That's interesting high kype, maybe I should leave them outside? Maybe it is powdery mildew? All I know is that I've always wanted a greenhouse and now I've got one it has caused me nothing but problems!! And not just the dahlias.
I think I'll stick to windowsills and airing cupboards in future

Fletch

 

fletch lift tubers rinse off and repot chaek for weavelf if so discard compost cover with fleece place in sun