Pollen incidence in central Arizona

Abstract

As to pollen distribution, central Arizona may be divided into two districts: the irrigated valleys with their adjacent fringe of desert, and the mountain country. The Salt River Valley, of which Phoenix is the central point, is taken as a type of the irrigated valleys. Its climatic conditions favor wind-pollinated plants. Species which for the most part are peculiar to the Southwest cause the hay fever and pollen asthma which are prevalent throughout most of the year. In this valley the cottonwood, ash, and olive trees cause mild symptoms in February, March, and April, respectively. Bermuda grass blooms from April 1 to late November, causing intense symptoms. There is no true ragweed in the valley, but members of an allied genus, Franseria, cause two ragweed seasons: the first, in March and April, from the desert franserias; the second, in September and October, from the false ragweed. Various species of Chenopodiales, including careless weed and Russian thistle, cause weed hay fever in summer; careless weed blooms in protected places most of the year. Visitors who are sensitized to the eastern ragweeds are not affected by the franserias unless they are group sensitized. Newcomers who had grass hay fever in the East do not react to the pollen of Bermuda grass until after several years of exposure. Visitors sensitive to pigweed or Russian thistle are not annoyed by pollen of the local species in winter, but they are liable to have symptoms in their first summer. All such group reactors are promptly relieved by intradermal treatment with extracts of the appropriate local pollens. In the mountain towns the hay fever season is relatively brief. Amaranth and Russian thistle in early summer, six-weeks grasses and false ragweed in late summer, account for nearly all cases. Only such visitors as have group sensitization or previous adequate exposure to local pollens are affected. In the resorts located in the pine forest and remote from cultivation, no pollen disease occurs.