The Germplasm Enhancement of Maize Project (GEM) is a cooperative effort of USDA-ARS, public and private sector scientists to broaden the genetic diversity of maize germplasm. Tropical maize germplasm is an important source of alleles for biotic and abiotic stress resistance and numerous value-added traits (VATS). Breeding with tropical maize is limited in the US due to photoperiod sensitivity, resulting in very late- or non-flowering, tall plants. An experiment was conducted in 2006 in Ames, IA, to determine if artificial control of daylength in field conditions could effectively reduce/eliminate photoperiod response of seven tropical genotypes, representing six maize races which originated from five countries. Treatment one consisted of seven A-frame “shade houses,” one meter in height, constructed from 22 mm galvanized pipe and black woven landscape fabric. Treatment two used 30 gallon galvanized cans, placed over 3-4 plants per genotype. Treatment three consisted of un-shaded plants. Shaded plants experienced eight hours of natural daylight daily (0700 - 1500 hours), from emergence to six weeks post-emergence. Shade treatments were equally effective in reducing photoperiod response of the genotypes, resulting in an average reduction of 17 days or 254 GDU to pollen shed, from 85 days (1099 GDU) to 68 days (845 GDU) for shaded entries. Shading treatments effectively reduced average plant and ear height by 103 and 98 cm, respectively. Average days to pollen shed of shaded tropical germplasm were four days (54 GDU) later than B73, and 21 days (323 GDU) later for un-shaded plants. Consistent use of shade structures to control daylength for a six week period after germination can facilitate use of exotic germplasm for Midwestern maize introgression programs. A larger version of the shade house will be used in 2007 to facilitate development of a ‘GEM tropical accession CUBA164 (PI 489361) x temperate inbreds' mapping population.