Ozone Ozone is the most widespread air pollutant that damages plants, including soybeans. Ozone is generated from the reaction of sunlight with nitrous oxides and oxygen in the presence of hydrocarbons. Such a mixture is commonly referred to as smog and arises primarily from automobile exhausts in urban areas. Most damage occurs when contaminated air stagnates over soybean fields. Prolonged exposure may result in reduced growth and yields depending on the cultivar and the stage of plant growth.
Damage is most severe when plants are growing under optimal conditions.
Drought-stressed plants are resistant. Soybeans are generally sensitive to ozone levels of 0.06 ppm or greater, although damage and symptom development vary depending on the cultivar. Leaves are most sensitive during the later stages of leaf expansion and symptoms appear 48 hours or more after exposure. For this reason, symptoms are first observed on older leaves. Injured leaves may ultimately exhibit chlorosis and die prematurely.