Cause Phytophthora sp., a fungus-like microorganism. This organism can survive as a resting structure (chlamydospores and oospores), as hyphae in the roots of diseased plants and in crop debris. It is easily spread in contaminated potting media, disease cuttings or liners and splashing or flowing water. Recycled irrigation water can also be a source. Cool, wet, or waterlogged soil favors disease development. The disease also can occur on sloping ground if soil stays excessively wet.
