Symptoms include white spots on leaves and stems that progress to sunken red or purple lesions and finally leaf necrosis.

Resistant varieties of tomato and cotton are common, though the pathogen remains an important disease in Chinese garlic cultivation.

Stemphylium solani is of greatest concern in tomatoes, potatoes, peppers, garlic, onions, and cotton, though a wide range of over 20 species have proven susceptible.

[1] In alliums, infection is first visible as oval white spots, 1–3 mm in length, scattered irregularly over the leaf surface.

These spots grow into red or purple colored lesions with a yellow margin and finally progress to leaf wilting and necrosis.

[2] In tomatoes, S. solani symptoms begin as round to oval dark specks on both sides of the leaf with older leaves being affected first.

[4] Stemphylium solani grown in potato sugar agar (PSA) culture are characteristically slow growing and darken with age, first to a yellow-brown color after 4 days and then red.

[9][10] Triazole has been shown in laboratory studies to effectively control mycelial growth and provides local systemic protection.

Diagnosis of specific species is determined based on distinct conidia and conidiophore morphology, though significant overlap in characteristics makes identification difficult.

[12] In addition to other strains of Stemphyllium, symptoms caused by S. solani can also be easily mistaken for Alternaria porri and Septoria Leaf Spot.