Title: Developing Metrics for Managing Soybean Aphids Authors
Submitted to: Review Article
Publication Type: Review Article
Publication Acceptance Date: December 6, 2009
Publication Date: February 2, 2010
Citation: Catangui, M.A., Beckendorf, E.A., Riedell, W.E. 2010. Developing Metrics for Managing Soybean Aphids. Crops and Soils. 43:21-30. Interpretive Summary: Plant injury caused by the soybean aphid (a serious pest of soybeans) can result in up to 75% yield loss. Soybean growers must effectively manage soybean aphid populations during the growing season to avoid these severe yield losses. The purpose of this article was to educate crop advisors on the relationships between soybean aphids and yields, on the economic injury levels (EIL) for use with this invasive pest, and on practical application of EIL to support decisions on the soybean aphid population management. Scientists from ARS and South Dakota State University documented strong mathematical relationships between soybean aphid numbers during specific soybean growth stages and the eventual yield at harvest. The stage-specific EIL were calculated, plotted and fitted with a symmetrical bell-shaped and logistic curve, respectively. Results indicate that scouting for the soybean aphids can be focused on or several days before the critical reproductive stages of soybean. In general, the soybean plant is tolerant of stress during the vegetative stages but is sensitive to it during the reproductive stages. The approximately 42-day duration from V5 through R5 is the logical time to manage for the soybean aphid. These experimental results were used to form the basis of a certified crop advisor self-study course and continuing education unit exam. Thus, this advancement in knowledge of soybean aphid – yield relationships was transferred not only to soybean producers, extension agents, and other scientists through professional journal articles and presentations to user groups, but also to certified crop advisors in the form of continuing education units in pest management.
Technical Abstract: Stage-specific economic injury levels form the basis of integrated pest management for soybean aphid (Aphis glycines Matsumura) in soybean (Glycine max L.). Experimental objectives were to develop a procedure for calculating economic injury levels of the soybean aphid specific to the R2 (full bloom), R4 (full pod), and R5 (beginning seed) soybean development stages using the law of the diminishing increment regression model. Soybean aphid population growth over time appeared to follow the symmetrical bell-shaped and logistic growth curve models. Peak soybean aphid population levels and rates of increase occurred at the R5 development stage and then declined sharply thereafter. Highest peak soybean aphid populations were 21,626 aphids per plant for infestations starting at V5, and 6446 aphids per plant for infestations starting at R2. Highest maximum aphid-days per plant recorded were 537,217 for V5-introduced soybean aphids and 148,609 aphid-days per plant for R2-introduced soybean aphids. On average, the calculated maximum possible yield loss was 75 % for soybean aphid infestations starting at the V5 (five node) stage and 48 % for soybean aphid infestations starting at the R2 stage. Interrelationships among the current or predicted market value of soybean, cost of soybean aphid control, and the yield potential of the soybean field were considered in the calculations of the stage-specific economic injury levels. Practical examples for calculating stage-specific economic injury levels are presented. Economic injury levels were calculated both as soybean aphids per plant and soybean aphid-days per plant. Use of these stage-specific economic injury levels may enable growers to manage soybean aphids more accurately.