The injury pattern in small grains and forage grasses generally occurs as a scattering of small, yellowish or white to tan flecks on one or both leaf surfaces. The flecks may later merge to form larger, bleached white to yellowish dead areas. Ozone usually attacks nearly mature leaves first, progressing to younger and older leaves. Ozone-killed tissues are readily infected by certain fungi. Persistence And Transmission.
Ozone is brought down from the stratosphere by vertical winds produced during electrical storms.
More importantly, it is produced when sunlight reacts with nitrogen oxides and hydrocarbons formed by refuse burning and the combustion of coal or petroleum fuels, especially the exhaust gases from internal-combustion engines. When oxidant levels in the air are high, more than 90 percent of the air is ozone. These levels are usually at their highest point in the afternoon and are relatively low at night. Varieties of the same plant can differ greatly in their susceptibility to ozone damage. Some examples include bean, grape, oat, onion, petunia, pines, potato, spinach, squash, sweet corn, and tobacco.