Dahlia - Knowledgebase Question

pittsburgh, pa
Question by lmccaul4
September 21, 2009
I have Dahlia's in pots and some in the ground. All were doing beautiful and bloomed profusely but now it seems some kind of plight has hit a couple of them. They got like a powdery coating on them and turned like a rusty color and have died. I have 2 tubors planted in ea pot and in both cases it happened to one of the plants in pot. I took off all damaged stalks which came off quite easy actually an just the tubor is left in the pots with one part of the stalk sticking up. How do I proceed with this? Do I let tubors in pot and keep watering as usual? Will the diseased tubors be ok to store as I had planned? How can I help to prevent what ever happened with them?
Oh!!! one thing I almost forgot to tell you was that when I noticed the white powder substance I sprayed plant with a spray I use on my Roses. This seems looking back now this could've been the wrong thing to do. These are the tall Dahlia's in peach, magenta and cream color and they put on quite a display this summer. I really hope to be able to salvage them for their beauty next year as well. Please any help you can give would be greatly appreciated. Do I let the Dahlia's that are still blooming that are in with what I call a diseased one just continued to grow and bloom? Ones planted in ground seem to be doing fine. Thank you for any help.

Answer from NGA
September 21, 2009


The first suggestion I have is to plant a single tuber in each container. This way each of the plants will have plenty of room to grow without begin overcrowded. And, if one develops a fungal disease, it won't spread to the rest of your plants. The white coating is a fungal disease called powdery mildew. It usually shows up in late summer when days are warm and nights are cool. Once you notice the disease, it has already infected your plant and it is difficult to control. The best thing to do is to cut away the affected foliage, which is what you did. To avoid next year, give your dahlias plenty of sunshine and ample room to grow. With the rest of your plants, wait until frost kills the tops down. When the tops freeze it signals the tubers to go into dormancy. After the tops die down, cut them off at soil level. Your tubers will need to be stored for the winter months. The best approach is to dig them out of the pots, brush off the excess potting soil and then store the tubers in dry peat moss. Check them periodically to make sure they are not shrivelling up. If they begin to get wrinkled you can mist them with plain water and return them to the peat moss. I layer mine in cardboard boxes with a few inches of peat moss between each layer. Keep them cool, but above freezing. You'll need to dig the tubers planted in the ground, as well. The tubers can take the cold temperatures but if the soil does not drain quickly they will turn to mush. It's safest to dig, store, and replant the tubers each year. Hope this answers all your questions!

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