A large theoretical literature in sociology connects increases in incarceration to contractions in the demand for labor. But previous research on how the labor market affects incarceration is often functionalist and seldom causal. We estimate the effect of a shock to the southern agricultural labor market during a time when planters exerted a clear influence over whether workers or potential workers were incarcerated. From 1915 to 1920, a beetle called the boll weevil spread across the state of Georgia, causing cotton yields and the demand for agricultural workers to fall. Using archival records of incarceration in Georgia, we find that the boll weevil infestation increased the Black prison admission rate for property crimes by more than a third. The infestation’s effects on whites and on prison admissions for other crimes were small and not statistically significant. Our analysis offers a conditional theory of the political economy of punishment, clarifies the relationship between incarceration and the economic institutions that replaced slavery, and contributes to a growing literature on incarceration and exploitation in the labor market.