Economic Impact of Sugarbeet Root Aphid (Homoptera: Aphididae) on Sugarbeet Yield and Quality in Southern Minnesota

Abstract

The economic impact of sugarbeet root aphid, Pemphigus betae Doane, infestations on sugarbeet yield and quality was studied during 1990 and 1991 in 11 commercial sugarbeet fields in southwestern Minnesota. Fields with one or more obvious infestation foci were selected for study. Severe aphid infestations were characterized by elliptical-shaped foci of stunted or wilted plants that averaged 14.8 m long and 9.0 m wide; average foci area was 104.6 m2 (0.0105 ha). Lengths of infestation foci were always parallel with row direction. An at-harvest, beet root rating system was developed to measure the impact of P. betae on yield and quality. Though gross yields were variable, sugar content and recoverable sugar per hectare were significantly reduced in 64% (seven of eleven) and 73% (eight of eleven) of the fields studied, respectively. Aphid-induced effects on quality parameters, other than sucrose, were characterized by lower levels of harmful amino nitrogen and potassium. No consistent relationship was observed for sodium. Negative effects of these factors, however, proved minimal when computing total sucrose losses to molasses (average 1-2%). Loss to molasses actually was less for aphid-infested beets in seven of eleven infestation foci. Therefore, sucrose content was the primary source of quality loss in this study. Losses in sucrose content and final recoverable sugar per hectare during the 2-yr study averaged 31 and 54%, respectively. In contrast to the 1990 season, maximum recoverable sucrose yields were significantly higher in 1991, and the rate of yield loss was initially lower (where root rating ≤2.0). Final yield loss rates for heavily infested beets (i.e., root rating ≥4.0), however, were similar. Results between years partially were explained by differences in precipitation (83 cm in 1991 versus 62 cm in 1990). Thus, separate yield loss formulas were developed to estimate monetary losses and an approximate economic injury level for P. betae.