Spider Mites?

Cheers,
Russ

Thank you for your reply, Russ. I shook for mites and inspected some leaves but I don't see evidence of them. What is striking to me is the regularity of the yellowing - from the outside edges to the center. Is this possibly a nutrient deficiency or heat/lack of water stress?

Hi Kimic-

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.....

I don't know much about viruses and find there is a lack of photos of known diseases affecting dahlias online, IMHO. Expense of confirming a diagnosis might enter into that. It would be a great project for the ADS or some other large dahlia group.

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.

Here is a link that might be useful: {{gwi:644228}}

I agree with Poochella. There are not enough pictures but I just lucked out and find what appears to be an article by a Washington State U. plant pathologist newly published (on-line, anyway) by the American Dahlia Society:

Here is a link that might be useful: Dahlia Mosaic Virus Pictures

Great find, Misslucinda. Those are a big improvement to have available for reference.

Thanks so much for the info. I have raised beds and one bed looks suspicious. Tubers are from all over so I can't pin it on one tuber. The leaves on all of the dahlias in that bed look like some of those pictures. I am going to try some iron on one to see what happens.

Thank you very much for your responses. I really appreciate it. I looked up images of chlorosis from an iron deficiency and that matches very well what my leaves look like. Tomorrow I will buy some chelated iron and see what happens. I looked closely at the leaves for smut and it looks a little different, but I will remove those just in case.

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.

Are you sure about that, kimnc? Your older leaves appear to be affected versus the younger ones and according to the U. of Ill. Extension:

' 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

Here is a link that might be useful: Illinois edu chlorosis article

People might want to see this again.

Bumping this thread-I noticed this evening that a few of my dahlias are suddenly starting to get yellowing leaves (over the last day literally it seems as I look at them daily). This is one pic of a plant that is otherwise thriving, has a few buds, about to bloom.

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.