SOIL-MANAGEMENT HISTORY AND THE ROLE OF PLANT MINERAL BALANCE AS A DETERMINANT OF MAIZE SUSCEPTIBILITY TO THE EUROPEAN CORN-BORER

Proponents of organic farming have long suggested that their methods p roduce ''healthy'' crops that are less susceptible to insects and dise ases. Experimental comparisons of European corn borer (ECB) egg-laying response to maize plants grown in a greenhouse in soil collected from either organically or conventionally managed farms provided evidence consistent with these assertions. in each of three paired comparisons, higher egg-laying occurred on plants in conventional soil. Subsequent studies suggested that differences in ECB ovipositional preference we re related to plant-mineral balance; a three-mineral quadratic model s howed strong predictive power for ECB oviposition. A role for plant mi nerals was also suggested in a study of paired maize fields with high and low ECB populations compared at three different geographic locatio ns. Significant differences in leaf-mineral profiles between fields we re measured that were consistent across locations. Based on these cumu lative findings, it is hypothesized that: (1) maize plants with an opt imal mineral balance show lower susceptibility to insect pests, (2) de termining the effects of minerals on susceptibility must include consi deration of both ratios and absolute levels, and (3) a more resistant physiological state is more likely in organically managed soils becaus e of the inherent greater capacity of these soils to buffer availabili ty of minerals to plants.