AbstractSoybean (Glycine maxL. Merr.) grain yields may be reduced when the plants lodge. The magnitude of yield reduction is dependent on the growth stage at which lodging occurs. The stage of plant development most vulnerable to yield reduction from lodging has not been conclusively determined. The objective of this two‐year study was to determine soybean yield reduction caused by simulated lodging at three stages of reproductive development: the onset of flowering (R1), beginning pod (R3) and beginning seed (R5). At each developmental stage the plants were lodged at either 45° or 90°. A natural lodging control and an artificially maintained erect treatment were included.The 1976 results indicated no yield differences due to any of the lodging treatments. In 1977, yields were significantly reduced for the R3 lodging treatments. Soybeans lodged 90° at the R1, R3, and R5 growth stages yielded 2.63, 1.88 and 2.26 Mg ha−1, respectively. The natural lodging and erect treatments yielded 2.73 and 2.43 Mg ha−1, respectively.Lodging treatments applied at the R1 stage produced plants with a two‐year average of 30 of their seeds on the main stems, compared to 62 of the seeds on the main stems for the R5 stage treatments. The percentage of seeds on the main stem was 69 on the erect plants, as compared with 45 on the 90° lodged plants. In 1977, lodging treatments also reduced pods per plant, seeds per plant, 100 seed weight and seed weigh
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