Roundup Ready® (RR) crops have been widely adopted because they provide significant benefits to growers, but glyphosate-resistant weeds threaten the sustainability of these benefits. Weed best-management practices (BMPs) help manage resistance, but could increase weed-control costs, limiting their adoption. We use survey results to explore how adoption of BMPs affects weed-management costs in corn, cotton, and soybeans, controlling for farmer and regional characteristics. More experienced growers had lower weed-control costs. Cleaning equipment, using herbicides with different modes of action, and using supplemental tillage are BMPs associated with increased costs for some crops, which may explain why they are less widely adopted than other BMPs. However, growers commonly use other weed BMPs that also increase costs. Regression results suggest adoption of RR crops reduces weed-control costs and that weed scouting reduces costs for cotton and soybean growers. Use of residual herbicides was associated with higher costs for cotton growers, but not for corn or soybean growers. Rotating RR and non-RR crops on the same acreage was associated with higher costs for soybeans, but not for corn or cotton growers.