Association Between Sugarbeet Root Yield and Sugarbeet Root Maggot (Diptera: Otitidae) Damage

Sugarbeet root maggot, Tetanops myopaeformis von RÖder, is a major insect pest of sugarbeet throughout much of North America. Root maggot damage is routinely rated on a 0 (no damage) to 5 (severe damage) scale. In 42 trials, the relationship between visual damage and root yield was examined. The mean damage rating in the absence of insecticides was 3.3 ± 0.4, compared with 1.7 ± 0.7 for the highest yielding treatment in each trial. Mean root yield of the highest yielding treatment in each trial was 48.8 8.9 Mg ha-1, compared with a mean of 29.0 ± 12.5Mg ha-1 when no insecticides were applied. Regression analyses within individual trials indicated that the yield loss associated with each increment of the damage rating scale fluctuated widely, ranging from near 0 to 15.7 ± 2.42 Mg ha-1 The percent yield reduction in the absence of insecticides ranged from 9.8 to 83.6% when compared with the treatment providing the most effective control in each test. These results are useful in estimating losses, developing recommendations, and providing a standard of comparison for alternative control strategies.