Plants dying midsummer and some white stuff
I've planted flowers in this bed, usually marigolds,for 20 years without problems. In midsummer 2010 the marigolds started to die. I didn't see any signs of disease, just dead plants. In 2011 I planted sunflowers and the same thing happened. Jst now, April 2012, I found a lot of the leftover mulch coated with something white. Some straggling root systems were also entirely white. I am (obviously) clueless here. Any help appreciated.