I have a slope where I have planted seed for sun flowers. The soil is poor and it is right next to where we park two of our vehicles. A week back I noticed the largest yellow sun flower was losing its yellow petals. The seed pod remains. Now I see where there are more flowers losing there petals. No worms, no crawley's, a few leaves turning brown or black. Some of the leaves have been chewed up by something but not all the plants. It has now gone to flowers of other color. ANY IDEAS???