Bacterial soft rot of Calla lily is caused by Erwinia carotovora . The soft rot infection begins in the upper portion of the corm and progresses upward into leaf and flower stalks or down into roots. Affected plants appear stunted and leaves turn yellow. The soft rot progresses throughout the tuber and plant eventually collapses and dies. The infected corm becomes soft, brown and watery. Sometimes infection starts at the edge of the petiole, which turns slimy. Leaves rot off at the base, flowers turn brown, stalks fall over. The disease spreads rapidly under warm, moist conditions.
This bacterium can survive in nonsusceptible host plants and for several years in the soil. As environmental conditions become favorable for bacterial growth, the bacteria multiply and cause disease.The addition of calcium in the media and avoiding excessive use of nitrogen fertilizer may help reduce the severity of soft rot caused by E. carotovora. Other management practices include: Discarding rotted corms, planting in well-drained soils, avoiding harvesting flowers when foliage is wet, avoiding injuring corms and keeping all production areas clean. It is also beneficial to dip corms in a copper fungicide before planting.