Alternaria Leaf Spot -- Alternaria panax
Host: Dizygotheca, Fatshedera spp., Fatsia, Polyscias spp. (Aralia), schefflera
Symptoms: This disease causes large, irregularly-shaped dark-brown spots to form on the leaves of plants and sometimes on their petioles and stems. Leaf drop commonly occurs with severe infections, giving the foliage a sparse appearance that is easily misdiagnosed as a symptom of root rot.
Conditions Favoring Disease: This disease is favored by wet conditions and temperatures between 65° and 86°F. Severe infections occur at temperatures between 75° to 80°F.
How Pathogen Survives/Disperses: The conidia of A. panax are carried by splashing water from fallen leaves on the ground to leaves several feet above the ground.
Photo and write up provided by Syngenta Professional Products