Symptoms resemble those of senescence and poor nutrition. Vegetation injury resulting from a build-up of oxidants in the air can occur over a large geographical region. Symptoms vary depending on the concentration of ozone in the air and the length of exposure, as stated before. Ozone injury occurs on the most recently emerged leaves. Typical ozone injury may not be evident on leaves exposed to a mixture of pollutants.
Symptoms differ in different areas of the province.
However, exposure to high levels of sulphur dioxides will result in light tan to white necrotic areas and yields may be reduced. Symptoms on nearby sensitive plants such as alfalfa, soybean, ragweed, and smartweed helps in confirming a diagnosis. Sources of sulphur dioxides are emissions from coal burning power plants, smelters and from the burning of petroleum. Losses in sensitive cultivars may be severe following exposure early in the season. Figure 10 Sulphur dioxide injury is reddish-brown between veins of smartweed of Ladies Thumb.