Establishing the causal effect of entry barriers on productivity poses a tricky identification challenge because entry barriers tend to be correlated with a wider set of government regulations and impediments that also affect productivity (e.g. taxation, monopoly power), or because an appropriate counter-factual does not exist. I circumvent these problems using a natural experiment in the US agricultural sector. This setting allows me to observe an exogenous change in entry barriers and the productivity response within two similar industries. The findings indicate that productivity increases substantially following the removal of entry barriers.