It is caused by Botrytis cinerea. It is found almost everywhere and can cause disease on almost every herbaceous ornamental plant species. It is a weak pathogen and usually will not infect healthy, undamaged plants. It will easily infect any part of a plant that is either wounded or beginning to die.
Cuttings are also susceptible.
The symptoms can vary widely depending on the host. In general, symptoms on leaves appear as watersoaked spots which become gray to brown as they enlarge to cover most of the leaf and cause it to wither. Spots often start at a point of injury. These spots may develop concentric rings of light and dark tissue, giving them a somewhat target-like appearance. On flowers, watersoaked to brown flecks which may enlarge rapidly to become large tan to brown areas, appear on the petals.