Management decisions on whether to treat soybean aphids or protect plants with fungicides will be affected by the soybean growth stage in a field during the next four weeks. As plants progress to the later reproductive stages (e.g., R5, R6, R7, etc.) risk of yield loss to either of these pest concerns declines. Currently, the soybean crop ranges from R2 to R3; some fields in the region will reach the R4 stage very, very soon. Insecticide treatments for R5 stage soybeans may respond positively to soybean aphid treatments when populations exceed threshold, however the level of the yield response has been less predictable. Treatments for aphids are not recommended beyond the R6 growth stage.

Soybean Growth stages from R1 to R6
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Reference:
W. R. Fehr, C.E. Caviness, D. T. Burmood, and J. S. Pennington. 1971. "Stage of development descriptions for soybeans, Glycine max (L.) Merrill." Crop Science 11:929-31