yellow/brown dying plants
Some of the plants in my flower garden turn yellow/brown. It starts at the lower stems and moves up to the entire plant. I do not think it is under or over watering because
other nearby plants are not affected. It happens mostly for "daisy-type" plants.
I hope you have some ideas about it-
From the limited description of the problem you have presented, it sounds like your plants could be experiencing a fungal or bacterial disease. You said your plant leaves turned yellow and then brown and this symptom begins at the bottom and progressed up the plant. Since you made no mention of leaf spots, leaf deformity, or powder-like growth covering the leaves or other leaf related issues, it sounds like the problem is spreading from the roots upward which is common with fungal and bacterial diseases such as wilts like fusarium and verticillium. Also, it is common with most plant diseases for some plants to be impacted more than others.
Having said the above, there really isn't enough information for me to tell you that your plants definitely have this disease or that disease. In fact, the problem may have nothing to do with a plant disease at all, but may be caused by some other non-disease related issue entirely such as soil fertility.
To help determine what problem your plants are experiencing I am providing you a really good link to a fact sheet from Virginia Tech University Extension on plant problem identification and diagnosis that I find very useful: http://www.pubs.ext.vt.edu/426/426-714/426-714.html
If your problem does turn out to be a wilt-type of fungal or bacterial disease, then a change in what plants you are planting or the use of a fungicide will be required. Remember, most fungicides work as preventative or control agents and not as disease cures, so they need to be applied before you see the problem and continued throughout the growing season.
Good luck in your flower garden the rest of this summer and fall and hopefully we'llhave a great fall weather-wise.