Comparisons of Soil and Seed Applied Systemic Insecticides to Control Beet Curly Top Virus in the San Joaquin Valley

Beet curly top virus (BCTV), a gemini virus, remains a problem for farmers in the San Joaquin Valley (SJV) of California. It is spread by the beet leaf hopper (Circulifer tene/lus Baker), which has become naturalized in the state. Recent dependence on sugarbeet cultivars without BCTV resistance has led to increased concern about the potential for a BCTV epidemic. Two trials were carried out in successive years in the western SJV to test the effects of alternative protective insecticides for control of BCTV on susceptible and resistant sugarbeet cultivars. Two rates ofimidicloprid applied as a seed treatment (45 g and 90 g a.i. per 100,000 seeds) were compared to the current standard treatment of phorate applied to soil at 83.8 g a. i. per 1000 m of row, and an untreated control. Natural BCTV infection occurred in both years, but the second trial took place during a major beet leafhopper population increase and infection occurred much earlier in crop development. Sugarbeet root and sugar yields declined linearly with increasing rates of infection (r2 = 0.856). Yields declined because roots were significantly smaller with the non-tolerant cultivar. Sugar percentage was unaffected by insecticide treatments, but differed by cultivar. Imidicloprid and phorate provided similar levels ofprotection to plants, but were not able to prevent large yield losses among susceptible cultivars. Plant resistance provided more protection than systemic