While chemical control of zebra mussels (Dreissena polymorpha) has proven effective in closed systems, the high dosages required for adult eradication restricts the use of chemical-based strategies in field management plans. One option is to identify the most chemical-sensitive life stage and tailor management techniques to control that life stage. This would optimize target efficacy while minimizing chemical release into the environment, risk to non-target species, and cost of chemical required. In this study, the relative sensitivity of D. polymorpha life stages was investigated from free gametes to 72-h old trochophores and adults, using cupric sulfate (CuSO₄) and the algaecide, Cutrine®-Ultra. In both forms of copper exposure, early life stages were orders of magnitude more sensitive than adults. For example, the highest 24-h LC₅₀ value for the early life stages to Cutrine®-Ultra was 13 μg Cu/L, while the adult 48-h LC₅₀ value was 1,214 μg Cu/L. Moreover, adults were highly resistant to short-term (24 h) exposures of Cutrine®-Ultra, even at much higher concentrations (4,630 μg Cu/L), while 24-h old D. polymorpha larvae showed 99% mortality after only 52 minutes of exposure to 331 μg Cu/L as Cutrine®-Ultra, a concentration well within the permitted label application. There were only marginal differences in sensitivity to CuSO₄ and Cutrine®-Ultra for larvae tested after fertilization; it is possible that Cutrine®-Ultra is more toxic than CuSO₄ at fertilization. Chemical management strategies targeting early larval stages of D. polymorpha are likely more cost-efficient and less prone to non-target environmental impact than strategies aimed at adults.