Abstract Potatoes were planted 3 May at the Research Farm of the Red River Valley Potato Growers Association, Grand Forks, ND. Plots were 4 rows wide, 60 ft (18.3 m) long, with 38 in (97 cm) spacing between rows and 12 in (30 cm) between plants. Plots were separated on all sides by 6.3 ft (1.9 m) of cultivated soil. The field was divided into three experiments each consisting of a complete randomized plot design with 5 replications. Few Colorado potato beetle adults were found in our field before mid-June. Egg masses were flagged 23 Jun and checked daily. Nine percent egg hatch was estimated to have occurred on 1 Jul, but heavy rains and wet field conditions prevented first application of insecticidal sprays until 7 Jul. Subsequent spray applications were made on 14, 21 Jul, 11 and 18 Aug. The July sprays were targeted against first generation larvae, the August applications against second generation larvae. All applications were made using a tractor-mounted boom sprayer, with a single Teejet nozzle over each row. Sprays were applied in 40 gal of water/acre (150 liters/ha) at 40 psi (275 kPa). Control evaluations were made on 16, 28 Jul, 13 and 27 Aug. Because Colorado potato beetle population pressure was very low and not uniformly distributed across plants, we did not count larvae directly. Instead, we scored 20 plants per plot for small larvae (1st and 2nd instar) and large larvae (3rd and 4th instar), for each using a \-4 scale: 1 = 0 insects, 2 = 1-5 insects, 3 = 5-9 insects, 4 = 10 or more insects. Adults were counted on a per plant basis. Data were also collected 9 Jul, but these data are not presented because population pressure was very low and not uniform across plots. Defoliation data were not recorded as treatment differences were not evident. For purposes of analysis of data on larvae, we used mean scores across sampling dates. Tuber yields were estimated by mechanical harvesting one row per plot on 9 Sep or 20 Sep.