The pathogen of this disease resides in the soil, plant residues, and greenhouse construction materials. It spreads through the wind and enters the plant tissue through stomata. It is more commonly observed in greenhouse conditions and can thrive in high humidity and a wide temperature range. It prefers temperatures between 20-25°C and humidity levels above 80%. Symptoms typically begin on the lower, older leaves. As a result of the infection starting on the underside of the leaf, pale yellow spots that gradually expand and spread across the entire leaf are observed. Additionally, velvet-like brown spots may appear on the lower surface of the leaf. The initially white spots turn into olive green and brown later on. The formation of a dense mass of spores in a fungal cover on the spots is a typical sign of this disease. Infected leaves turn yellow and dry prematurely but do not fall off. Controlling the disease is possible through greenhouse ventilation. Fungicides may not be effective when applied at temperatures below 14°C. It is important to ensure that the applied fungicide reaches the underside of the leaves.