A study unusually published as correspondence rather than as an article examined maize modified to express four traits (resistance to European corn borer, resistance to corn root worm, glyphosate tolerance and glyfosinate tolerance) singly and in combination in Wisconsin fields from 1990–2010. The variance in yield from year to year was reduced, equivalent to a yield increase of 0.8–4.2 bushels per acre. Bushel per acre yield changes were +6.4 for European corn borer resistance, +5.76 for glufosinate tolerance, −5.98 for glyphosate tolerance and −12.22 for corn rootworm resistance. The study found interactions among the genes in multi-trait hybrid strains, such that the net effect varied from the sum of the individual effects. For example, the combination of European corn borer resistance and glufosinate tolerance increased yields by 3.13, smaller than either of the individual traits