Seasonal migration plays a critical role in stabilizing rural economies and sustaining the livelihoods of agricultural households. Violence and civil conflict have long been thought to disrupt these labor flows, but this hypothesis has historically been hard to test given the lack of reliable data on migration in conflict zones. Focusing on Afghanistan in the 8-year period prior to the Taliban's takeover in 2021, we first demonstrate how satellite imagery can be used to infer the timing of the opium harvest, which employs a large number of seasonal workers in relatively well-paid jobs. We then use a dataset of nationwide mobile phone records to characterize the migration response to this harvest, and examine whether and how violence and civil conflict disrupt this migration. We find that, on average, districts with high levels of poppy cultivation receive significantly more seasonal migrants than districts with no poppy cultivation. These labor flows are surprisingly resilient to idiosyncratic violent events at the source or destination, including extreme violence resulting in large numbers of fatalities. However, seasonal migration is affected by longer-term patterns of conflict, such as the extent of Taliban control in origin and destination locations.