The Q&A Archives: Fungus On Dahlia Tubers

Question: I just found that all of my approximately 80 clusters of dahlia tubers are covered with a fungal growth and have rotted over the winter. They were properly dug and stored in sawdust last fall after being hit by frost. Most of these were over 50 years old and some were purchased new in 2000. I was able to salvage a few individual tubers which I understand can be propagated. Other than dusting the tubers with a fungicide before storage (which has never been done)can you recommend anything else to prevent this from happening? Should the soil be treated before planting at the same site this year?

Answer: How disappointing! It sounds as if you stored them correctly. Dusting with fungicide before storage isn't usually recommended. Here's the best way to prepare them for storage, according to Judy Glattstein and NGA writing in "Flowering Bulbs for Dummies."

Shake off excess dirt and clip back any mushy leaves.
Allow them to dry off a bit for a few days.
Pack them in a cardboard box lined with a perforated plastic bag. Fill with dry peat moss, wood shavings, buckwheat hulls, vermiculite, etc.
Don't let individual roots touch each other. It one starts to rot, it's less likely to spread to all others.
Punch a few holes in the plastic so moisture can escape, but not so many holes that the roots dry up.
Keep the box in a cool, dry place, such as the wall of an attached, unheated garage that adjoins the house.
Check periodically to make sure the material is not wet or the roots are not shriveling from dryness.

Typically it's not a good idea to plant in the same area year after year, as plant-specific diseases can build up. I suggest that you take a sample of the diseased tubers and your soil to the County Cooperative Extension office for diagnosis. Then they can tell you specifically what treatment might be available. They are at 8012 Vinecrest Ave., Ste. 1, Louisville, 502-425-4482. Good luck!

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