Beyond immediate loss of life and physical destruction, civil conflict affects societies in myriad ways, many of which are difficult to quantify. In this work, we study the effect of conflict on economic activity, in the form of seasonal labor migration. The context that we study is opium poppy cultivation in Afghanistan, an illicit industry that employs a large number of seasonal workers in well-paid jobs. We use satellite imagery to infer peak agricultural activity, and a measurement strategy that exploits this timing, to estimate seasonal labor flows using anonymized mobile phone metadata. We find that on average, high-poppy cultivating districts have excess in-migration during the harvest of 3% more than the baseline, compared to districts with no poppy cultivation. These labor flows are resilient to shorter-term occurrences of violent events, but are shaped by longer-term patterns of conflict. In this particular context, the presence of insurgents is associated with larger labor flows, both at the source and at the destination.