I have been searching around the internet to diagnose this leaf problem on my Ellen Houston (pictures below). It doesn't have the pattern of a mosaic virus, at least not from what I can tell. Some flowers are also turning brown quickly or opening partially brown and "crispy." I see it on a few lower leaves most intensely, but as you can see, there are some leaves at the top of the plant developing it. Any help you could offer would be greatly appreciated. Thank you!

Cheers,
Russ

The chloritic leaves and curling would appear indicative of a dahlia virus to me. Apparently, sometimes the new growth out reaches the virus leaving the oldest, lowest laterals the first victims. This could be one explanation why I am reading more and more about taking root cuttings and planting those instead. Anyway, you have some very attractive blooms and may have for a period of time. BTW, you are supposed to destroy infected leaf material and tubers. (AKA don't compost).

I am having a similar problem here in New York which I find very troubling as I ordered all new tubers this year and can find no evidence of leaf-hoppers (a common carrier of the virus) or of aphids (ditto)and two of my affected plants are in a huge wash tub which I sterilized prior to planting.

I am hoping if I bounce your thread higher on the list Plantlady and/or Poochella might respond to you also(as they are voices of great experience). If not, try the U of Washington and Oregon horticulture websites for pictures. I know a Virus hit the Canna world over the past five years or so and I unknowingly purchased infected Canna tubers. Stuff happens. Yuck.

Best of luck (to you me and the rest of us who love the tricky blooms),

Lucinda

...Off to slaughter the dreaded Japanese Beetle.....

First photo, far left large leaf in the middle: the dark spot surrounded by a lighter ring looks like smut to me. They start out light green and brown from the inside out. See the link. The advice is to remove the bottom leaves (it's a soilborne fungus,) destroy all infected material and use a copperbased fungicide if you desire. Crop rotation is also advised and that's what I've read and done because I think I have it. Bummer.
One page on dahlia smut
http://www.members.shaw.ca/hydahlia/smut.html

I had some yellowing on a plant one year looking much like your last photo with blooms, though my plant was just a foot tall or so. I took Plantlady's advice watering in some chelated iron. It greened up and went on to prosper in no time with no return of the yellow.

Good luck with whatever it is that ails your otherwise beautiful dahlia.

Thanks again! I was about to rip out my plant, but the images look much closer to chlorosis than DMV. I will try the iron and let you know what happens.

' Manganese or zinc deficiencies in the plant will also cause chlorosis. Iron chlorosis starts on the younger or terminal leaves and later works inward to the older leaves. However, manganese and zinc deficiencies develop on the inner or the older leaves first and then progress outward.'

Further, Cornell recommends you do a soil test prior to treatment: http://plantclinic.cornell.edu/FactSheets/microchlorosis/microchlorosis.htm

And Wikipedia states that waterlogged roots can also be the cause and we in the northeast at least have certainly had an extremely wet and cool summer thus far. Wish I could hyperlink this as well:

http://en.wikipedia.org/wiki/Chlorosis

From what I've gleaned thus far DMV can be identified by a yellowing of the veins of the leaves whereas chlorosis by an interveinal yellowing. (See the Wiki article for a decent photograph.

Let us know your progress. Good Luck,

Lucinda

Pics for the tomato spotted virus seem like almost any yellowing leaf could be it, but I'm wondering about iron or nitrogen deficiency as I have mostly been fertilizing with a bloom fertilizer.

I'm hesitant to just assume tomato virus and toss the plant since it's otherwise extremely healthy with lots of growth--should I try iron and see or nitrogen or ? Also it's been pretty dry the last week though I have been watering, so no leaf droop.

Any suggestions appreciated.