Leaves of sensitive species develop a slightly oily or waxy appearance two to three hours after exposure. Glazed symptoms develop gradually with the advanced bronzing stage following after two or three days. Very young and the most mature leaves are resistant. Many other substances may be released to the atmosphere and produce damage to plants. These all produce characteristic symptoms.
Plants vary in their susceptibility to different pollutants.
Those observing and diagnosing air pollution injury should be aware that many things may resemble symptoms produced by air pollutants. Care should be taken in diagnosis. They are found everywhere and are numerous in any place where sufficient moisture is present to support their growth. Their habit of growing profusely in evaporative coolers and on rock houses and sidewalks often makes them very bothersome. Although copper fungicides will do an excellent job for controlling algae, in most instances it is not always desirable.