In the 1940s, research agronomists here began to notice some mysterious damage to southern California trees. Puzzled, they called it X disease. How smog affects agriculture is still not completely understood. But as development, industrial growth, and traffic have spread from cities into rural areas nationwide, the question has become a concern well beyond the borders of Los Angeles County.
A scientist at the University of California, Riverside, reports that in the state's breadbasket, the San Joaquin Valley, smog damage cuts the cotton crop by as much as 20 percent a year.
The findings don't come as a surprise to cotton growers. Smog damage has been measured before, but it is an elusive factor to test for, and results have been erratic. These field tests are considered more accurate and definitive than any in the past.
O.Clifton Taylor, whose work is part of a nationwide assessment of crop losses to air pollution, notes that California produces more than a quarter of the nation's cotton. The losses here to smog cost growers about $200 million a year, he says.
Nationally, the dirty air may cost soybean farmers more. ''California certainly has the largest concentration of oxidants in the air, especially in the south coast basin, but the total economic damage may be higher to Midwestern soybeans,'' says Eric Preston, project manager of the study sponsored by the Environmental Protection Agency (EPA).
The soybean plant is sensitive to smog, and in Illinois, Indiana, and Iowa where much soybean is grown, the smog is year-round.
The air is not getting any cleaner in rural areas like California's central valleys. More traffic and more industry have raised the smog levels slightly in recent years. Since there are no chemicals or farming techniques that can combat smog, the option is to develop tougher strains of plants, says Dr. Taylor.
So far, most headway toward developing smog-resistant crops has been through the back door. Breeders have worked harder to make plants more resistant to worms and wilting, but tests of new strains in smoggy California fields automatically become a smog test as well.
So, not surprisingly, cotton varieties developed in the San Joaquin Valley are more robust in dirty air than are varieties that hail from the US rain belt.
Progress is slow, and the work is still in its early stages. ''There is only one public breeder of cotton in California, and that's me,'' says Gus Hyer, research agronomist with the US Department of Agriculture. And he has had to drop his work on smog-resistance for now to work on other projects.
''In a breeding program, it takes a couple years to develop good measurement techniques,'' he says, ''and a good three years after that to know if we're making any progress.''
Taylor is now testing alfalfa, as part of the EPA tests covering the nation's top 10 crops.