Marigold death

Some of my potted marigolds have recently suffered a major ugly wilting of their foliage, although the blooms were pretty much unaffected. This kind of goes along with all the mildew I've had this past summer. I just read that you need to give your potted plants lots of space to breathe. This wouldn't work very well for me, as I've simply collected far too many plants and run out of space! Marigolds have never been entirely fool-proof for me, but overall they are quite gratifying. I am now wondering If I need to toss all the soil in the pots with the affected plants. I usually re-use at least some of the soil when repotting. I go through it and remove clumps of roots and other undesirable stuff, but do you think whatever is killing my plants will remain in the soil? Could I just give it a good dose of an antifungal? Ideas?

Marigolds seem to like warmth. In Sept, we had multiple nights where it got down below 40, and the tomatoes and other tropical plants are suffering, getting fungal blights as is usual in the fall. I would chalk it up to the early chilly weather and drought, stressing the marigolds and making them susceptible to infection.
You could try an antifungal, there are both sprays and systemic drenches that you pour on the soil. I don't usually do this out of doors for fear of killing desirable organisms, and inadvertently poisoning little creatures. However when I have used them it has helped. I have used both kinds.
I think fungal spores are everywhere, and generally land on a plant by wafting through the air, splashed up from soil onto leaves, or on tiny feet of bugs, rather than growing up into roots. Since you like to reuse some of the potting soil for more than one year, if you reuse the bottom half, and pour new stuff on top, fungal spores would not be splashed up onto the leaves next year, and overwhelm the new plants.

Thanks, Pistil. Today I discovered that even the buttercups that think they are my lawn (and they may be right) are turning white. I don't think they crossbred with the Dusty Miller. I used to think Dusty Miller was the person who discovered them, but now I'm thinking it was more probably an allusion to a flour-covered miller. Now there you'd never know if you had a fungus.....BTW, have you ever tried the baking soda/detergent spray combo for fungus? For me it's been problematic. First there was the problem of getting the soda to get thru the sprayer (blender took care of that). Then I may have kind of drowned them, which probably sealed their fate. I don't like to, but this year I did buy a spray bottle of antifungal. It didn't go far, and I couldn't tell how much was enough. Couldn't get to the bottom of the bottle with the sprayer, so bought more. Do you need to remove all affected foliage? Part of my problem may be not having my reading glasses with me!

Hi velveteena-
On my drive home this morning I was listening to 'Gardening with Cisco', our local gardening guru. A caller asked about bad powdery mildew on her plants this year. Cisco confirmed what I thought
1- It is due to the heat and drought this year.
2- powdery mildew is fundamentally different from most fungal infections, the fungal hyphae can only penetrate the leaves of a dehydrated plant, so underwatering is the basic problem, the opposite of many other fungi.
3- Once the leaves are significantly infected, it is pretty hopeless, but he did say if you notice it really early the baking soda thing helps, but then you have to do it every 2 weeks. I have never tried it.
4- He said you do NOT have to get rid of the soil, but do a meticulous fall cleanup and remove all of the dead/dying plant parts, to reduce the spores for next year.
5- Next year do a better job watering to prevent it from happening again. He likes soaker hoses for the garden. For pots I guess an automatic watering system might help.

Fortunately the growing season is about done for, and I only lost the one pot, and a tiny bit of another. Other than that. the flowers were pure gold!