From scenarios of warming, scientists can foresee that pests favored by cool weather will retreat from while those favored by warm weather will advance toward the poles. The record shows, however, that pests are shifty. Unforeseen, not foreseen, pests cause the disastrous outbreaks and epidemics in both agriculture and medicine. New, surprising fungi caused both the Irish potato famine of the 1840s and the Southern corn leaf blight of 1970.
In 1976, an agricultural committee wrote, ``History warns that new pests will appear but provides no data for a model that tells where and when newcomers will appear or what they will be like. The required warning system of sharp, exploring eyes in the field is old-fashioned but remains our most effective approach" (National Research Council, 1976[Cou76], 128). Thirteen years later, a medical committee (Lederberg et al., 1992[Led92]) reinforced the finding of the agricultural by concluding that tracking outbreaks is the key to preparation for new microbial threats. Pests of plants must be placed among surprises.
Surprises by pests certainly will lower useful yield and press on the supply of cropland. Instantaneous warnings of new diseases of plants, as of humans, prompt research for ways to slow new pests. Development of remedies can reasonably be hoped to make pest epidemics less likely to decimate food supply now than at the dawn of plant pathology in the nineteenth century. New remedies can reasonably be hoped to duplicate the control of Southern corn leaf blight in a single year, 1970-1971. Nevertheless, surprising pests could lessen our ability to spare cropland for Nature.