Dahlia Garden a Complete Failure!

raymondo17(z9 Sacramento)September 20, 2007

I planted an extensive dahlia garden this year that, unfortunately, met with complete disaster. I planted 22 tubers, all of which came up and did very well -- for a while. Then the plants started turning brown and crispy from the bottoms up. Some folks suggested that the hot Sacramento sun might be too much (they're in a full-sun location). But if it was too much hot sun, wouldn't they have crispified from the top downward, not the other way around?

Someone else suggested the redwood bark chips I laid down as a mulch was depleting the nitrogen. Could this be the culprit?

The dahlias are in their own section of a border garden. Most of the other plants had no problems at all. It was just the dahlias that turned into dried up twigs.

Any input gratefully appreciated.

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Sounds like spider mites to me.

    Bookmark   September 20, 2007 at 11:56PM
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caavonldy(8/9 N CA)

I live about 100 mi north of Sacramento and the hot sun hasn't bothered my dahlias at all. They seem to love the heat as long as they get enough water.

    Bookmark   September 21, 2007 at 12:09AM
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raymondo17(z9 Sacramento)

They're on a drip system getting ample water, so I don't think that's it. They've been flowering nicely, but then the brown crispiness works its way up to the top of the plant, killing the whole thing.

How can I tell if it's spider mites? Look for fine webs?

Could it be some kind of disease?

Thanks for the input.

    Bookmark   September 21, 2007 at 10:05AM
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I believe spider mite damage will look something like this..

It's hard to get a clear close-up on these pics. However, if you look on the underside of the leaves, you should see the very fine webbing. Hope this helps.

    Bookmark   September 21, 2007 at 10:41AM
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raymondo17(z9 Sacramento)

Hmmmm, they didn't quite look like that. Here are some lousy photos that might help.

Here is a link that might be useful: Sick Dahlia 1

    Bookmark   September 21, 2007 at 11:17AM
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Did you check the underside of the leaves for webbing? If there's no webbing, I doubt it's spider mites. Cannot call myself a dahlia expert, just telling you from my horrific experience with dahlia pests and diseases this year. In your 2nd picture, there's a leaf at the very bottom to the right of the cream colored bloom....if you look closely it kind of looks like damage from leaf miners. I would google some pics for leaf miner damage on dahlias. Maybe, also check with the folks at the Garden Clinic forum.

    Bookmark   September 21, 2007 at 1:53PM
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I'm about an hour north of sacramento in Chico and several of my dahlias look just like your first picture. This is my first year with dahlias so I know very little about them, but it seemed like the leaves had very fine webbing on them which led me to believe they had spider mites. It usually started on just a small area & even after cutting off the affected leaves, it would still spread over the entire plant. One plant i ended up completely cutting to the ground and the growth that came back up seems to be healthier. May not be worth it to do that now though with fall upon us.

    Bookmark   September 21, 2007 at 3:31PM
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Call your county extension office and see if they can identify the problem from the picture are if they require that you send them the plant.

    Bookmark   September 28, 2007 at 9:45AM
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I believe you might have powdery mildew on your plants. If you had looked at your plants early in the season, you would have probably seen leaves with what appears to be a powdery dusting over the leaves. As the disease develops and gets worse, the leaves wilt and brown, starting from the bottom.

Hot, humid weather means the leaves never get cleaned, and neither are they dried thoroughly.

Increasing air flow by pruning and planting plants farther apart, occasionally rinsing leaves with strong sprays of water to remove inoculum (do this on a morning of a dry day to give the leaves a chance to dry throughly before evening), immediate removal of dying leaves, thorough cleanup this fall to reduce as much inoculum as possible, and optimism that the weather will be less conducive to development of this disease next year may help. Their are fungicides that can be used, but they must be used early BEFORE symptoms: they prevent, they do not cure. Better cultural conditions are usually sufficient.

    Bookmark   October 6, 2007 at 9:53AM
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I think you might have a fungal infection in your soil.
Better check your County Extension

    Bookmark   October 6, 2007 at 7:50PM
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raymondo17(z9 Sacramento)

Thank you all for taking the time to post some suggestions. :)

I examined the leaves and didn't see any signs of webbing or spider mites. The leaf miner photos I found showed little trails showing a kind of surface path the leaf miner "mined" on the leaf, and I saw none of that on my leaves. Powdery mildew might be the culprit. I did see a *few* leaves with a white powdery surface, but that was only late in the season. Plus, we don't have much humidity in my region, though some parts of the dahlia garden do catch some lawn sprinkler overspray. Bad, I know, but unavoidable. The fungal infection in the soil is also a contender, but this is a brand new garden in heavily amended soil that used to be a lawn. Plus, none of the other surrounding non-dahlia plants showed any signs of sickness. Wouldn't a fungal infection have affected them as well?


    Bookmark   October 9, 2007 at 2:28PM
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Looks like you need to spray for spider mites, and then fertilize heavily. Mine did the same while I was on a three week vacation. Dahlia society told me what to do, an it worked.

    Bookmark   October 10, 2007 at 11:33AM
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