This paper presents a choice experiment designed to estimate the willingness-to-pay (WTP) of rural farmers to mitigate damages caused by invasive plant species, particularly Mikania micrantha, in the buffer zone of the Chitwan National Park in Nepal. In subsistence economies, where households face cash constraints, labor contributions can be used to estimate WTP for environmental services. However, since the opportunity cost of time varies across individuals, aggregating individual willingness to contribute time to obtain social welfare is not straightforward. In this study, the social opportunity cost of time spent in invasive species management is estimated by using two cost attributes, labor contribution and membership fees. The results suggest that the estimated shadow value of time is 47% of the daily wage rate. The results also reveal that rural farmers are willing to pay NRs. 2,382 (USD 31) per year for Mikania management activities. Households are willing to make cash and labor contributions because they expect that invasive species management will reduce forest product collection time and increase tourism.