Air Pollution Damage to Annual Flowers

Some landscape sites, especially in highly urbanized area, are subjected to significant levels of air pollution. Researchers at universities in smog-prone areas have studied and documented air pollution damage to plants. These areas include the San Gabriel and the San Bernadino mountains of Southern California.

Most air pollution comes from automobile exhaust. Sunlight in the presence of exhaust promotes the formation of a gas called ozone that injures plants. Other pollutants are sulfur dioxide, and peroxyacetyl nitrate (PAN). Symptoms of sulfur dioxide injury include necrotic (dead) spots between the major veins, where the tissue turns light tan and papery in texture.

The most common symptom of exposure to O³ is the formation of tiny, light-colored flecks or spots on the upper surfaces of affected leaves, similar to spider mite damage. PAN injury is expressed as silvering, glazing, bronzing, and sometimes death of the lower leaf surfaces.

Bedding plants do exhibit relative sensitivity and tolerance to these materials and, if pollutants are a problem, plants should be selected accordingly.

Annuals sensitive to sulfur dioxide include aster, begonia, bachelor's button, china aster, coleus, cosmos, geranium, marigold, poppy, and zinnia. The most common symptom of exposure to ozone is the formation of tiny, light-colored flecks or spots (similar to spider mite damage) on the upper surfaces of affected leaves.

Annuals sensitive to ozone include ageratum, aster, begonia, marigold, pansy, petunia, and salvia. Symptoms of PAN injury are expressed as silvering, glazing, or bronzing of the lower leaf surfaces and sometimes leaf death. Annual flowers sensitive to PAN include aster, impatiens, petunia, salvia, and snapdragon.