One of my potted dahlias on my balcony died suddenly and dramatically. It has been blooming very well over the last two months. It was perfectly fine three days ago, then suddenly, all flower buds and leaves died. Not a single leaf left! Here are the photos from three days ago and today. I have another Dahlia adjacent to it. That one had aphids, so I sprayed my entire balcony with regular horticultural oil spray (Safer's End All miticide). The one with aphids has now recovered. But this one that didn't have aphids completely died. Does anyone have an idea about the cause? Is there any chance of revival, or I should just toss this dahlia?
Did you use this sprayer for spraying herbicides (glyphosate, for instance) earlier? If there was a small amount of residues of glyphosate in the sprayer, and this plant was the first you sprayed, then all sounds logical. If your Dahlia has tubers, then you may still succeed to regrow it from tubers.
Could it be that one plant was exposed to the sun during and after application of the miticide while the other remained in shade?
I agree it is very unusual for a plant to wither up and die that suddenly. In my experience, it takes glyphosate more than 3 days to kill a plant so thoroughly. Even so, the fact your dahlia died right after you sprayed the area seems more than a coincidence. Why not take a look at the tuber and roots; if the tuber still feels firm, replant it and hope it continues to grow.
I would suspect fungus. Dahlias are quite susceptible to fungus. Examine the roots and tubers. If they are mushy then definitely get rid of the soil and all plant parts, then disinfect the pot using 10% bleach solution before using the pot again.
Update: the other dahlia has now died too! (The one previously infested with aphids). The spray I used is the End All brand of miticide/insecticide/acaricide, it contains only horticultural oils, no herbicide. These potted dahlias are surrounded by other potted perennials: gerbers, kalanchoes, kinnikinnick, echeveria, and other herbs. The other plants also received the spray and are all fine. The kinnikinnick also got aphids, and is now cured. Thank you everyone for the quick response! I will now dig up the roots and see if the tubers are still okay.
