Effects of tillage, irrigation, and nitrogen on insect pests in sugar beet

Despite the agronomic benefits of conservation tillage in sugar beet, much is not yet understood about the effects of tillage type, irrigation rate, and fertilizer rate on sugar yield or insect pests. We conducted a 2-year study in Idaho to determine how these parameters affected yield and insect pest densities. We compared three tillage treatments [conventional tillage (CT), strip tillage (ST), and direct seed (DS)], three irrigation treatments [50, 100, and 150% of sugar beet evapotranspiration (ET) for CT sugar beet], and four N fertility rates [60, 80, 100, and 120% of the recommended rate for CT sugar beets]. Root yield was highest in CT and lowest in DS, but estimated recoverable sucrose did not differ among tillage types. Sugar yield showed no significant interactions among tillage, irrigation, and N rates suggesting recommendations do not need to be adjusted for tillage type. Insect pest responses varied among species and years. In one year, beet leafminer (Pegomya betae) egg and larval densities were greatest in CT compared with DS and ST. In one year, bean aphid (Aphis fabae) densities differed among N treatments, with the highest counts observed in the high N treatment followed by the low N treatment. Sugar beet root aphid ratings (Pemphigus betae) did not differ among treatments. The results presented here suggest that Idaho sugar beet can be produced with conservation tillage under a range of irrigation and N fertility regimes without compromising sugar yield or insect pest management programs.