Eight treatment combinations of insecticides and winter and summer annual weed herbicides were applied to alfalfa plots to investigate the impact of weed management practices and insecticide use on density and intensity of populations of the potato leafhopper (PLH),Empoasca fabae(Harris). PLH nymph and adult populations were monitored during the growth seasons of 1983–85. Adult population densities (PLH per m2) and intensities (PLH per stem and PLH per gram of alfalfa) were lower in plots receiving treatments for control of winter annual weeds (grass-infested alfalfa) and were higher in plots treated with both winter and summer annual weed controls (weed-free plots). Weed control measures were not a significant influence on population densities and intensities of PLH nymphs. Where insecticides were applied, neither nymph nor adult abundance and intensity were affected by weed-control treatments. Nymph and adult density varied within alfalfa growth periods and between seasons. Nymphs were more abundant during the second growth period, whereas adults reached their peak density during the third alfalfa growth period. Therefore, field scouting to determine PLH populations should be intensified during these periods.