Phenotypically plastic increases in extrafloral nectary (EFN) production after defoliation have been shown in several studies, presumably as a response to attract ants as herbivore predators. As EFNs may be costly to produce and maintain, induction of EFNs as needed may reduce their overall costs. We surveyed trembling aspen (Populus tremuloides Michx.) in a common garden to examine clonal differences in EFN production and preliminary evidence suggests that aspen with the greatest number of nectaries also had the lowest level of defensive chemicals, suggesting a potential tradeoff between EFN and defensive chemical production. In a second study using a cohort of aspen genotypes that received either defoliation or no defoliation, we determined that some clones of defoliated aspen increased nectary production whereas others did not. Genotypes with the lowest “constitutive” numbers of nectaries showed the largest induction response. These results suggest that some aspen genotypes increase their EFN production when the risk of herbivory is greatest, likely reducing the cost of maintaining high numbers of EFNs. If the presence of EFNs reduces the fitness loss due to herbivory (due to ant predation of herbivores), then EFN induction could be considered an example of induced defense against herbivores.