Most popular indices in use today that address agricultural drought [e.g., the Palmer Drought Severity Index (PDSI) and the Crop Moisture Index (CMI)) do not consider specific crop responses to the drought event. Thus, values produced by indices such as the PDSI and CMI cannot be directly linked to drought impacts on crop production and yield since each crop responds differently to moisture and heat stress. This paper presents a new drought index that, unlike other drought indices, is specific to a single crop (com-Zea mays L.) and takes into consideration water use during specific periods of growth. The Crop-Specific Drought Index (CSDI) model was developed with 8

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Genetically engineered maize (Zea mays) containing insecticidal endotoxin proteins from Bacillus thuringiensis (Bt) delta-endotoxin proteins has been adopted widely in the Midwestern United States. The proteins are toxic to several lepidopteran species and because a variety of maize tissues, including pollen, may express the endotoxins, the probability of exposure to nontarget species, including endangered species, needs to be understood. The objective of this study was to assess the potential temporal and spatial exposure of endangered Karner blue butterfly larvae (Lycaeides melissa samuelis) to Bt maize pollen in Wisconsin using probabilistic exposure techniques and geographic information systems analysis. Based on degree-day modeling of butterfly phenology and maize pollen shed, there is some potential for temporal exposure of larvae to maize pollen. However, in the majority of years and locations, maize pollen shed most likely will occur after the majority of larval feeding on wild lupine (Lupinus perennis). The spatial analysis indicates that some Karner blue butterfly populations occur in close proximity to maize fields, but in the vast majority of cases the butterfly's host plant and maize fields are separated by more than 500 m. A small number of potential or existing Karner blue butterfly sites are located near maize fields, including sites in two of the four counties where temporal overlap is most likely. The exposure assessment indicates that these two counties should receive the highest priority to determine if Karner blue butterfly larvae are actually at risk and then, if needed, to reduce or prevent exposure.

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How drought is perceived, and defined, detennines the likely re· sponse of decision makers to a drought event. Since drought response is usually based on some type of assessment of the severity and du· ration of tbe event, a critical element of a drought response strategy lies in the incorporation of objective and reliable impact assessment techniques. However, a long-standing problem in responding to past droughts has been tbe lack of reliable techniques for monitoring tbe drought event and assessing probable impacts. This paper describes a new method to reliably monitor and assess weather's probable im· pact on com (Zea rrwys L.) yields, on a crop reporting district (CRD) level, any time during tbe growing season. The 1990 growing season was used to demonstrate the ability of the crop-specific drought index (CSDI) to monitor and assess the condition of East Central Nebraska's corn crop every 10 days, starting 17 June, until a definitive projected CSDI value became established. A 3·wk bot and dry spell (24 mm of rainfall during the 3-wk period 28 June-17 July) that immediately preceded silking resulted in a 17 July CSDI assessment, based on the climatological record of the CRD, that projected yields to be only 63% of the maximum yield previously attained in this CRD. However, a substantial rainfall event during the week of silking alleviated the stressful conditions, and by the beginning of the early grain fill period (blister stage), a 6 August CSDI assessment projected the final CSDI value to within 3% of the actual CSDI (projected and actual yields were 86 and 83%, respectively, of the maximum yield previously at· tained in Nebraska's East Central CRD). The results of this study demonstrate that the CSDI can monitor and assess weather's impact on com yields on a CRD level.