Will late-planted soybeans mature before a killing frost?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

Planting delays and the cool weather have some producers wondering if their soybeans will reach physiological maturity before the first killing frost occurs this fall. Physiological maturity is the growth stage where half the plants have one normal pod that has reached its mature color. Any stress occurring after this point will not reduce yields.

Soybean development is determined by photoperiod (day length) and temperature. Temperature is the dominating factor from germination to flower initiation. For example, planting into warm soil temperatures can speed up soybean emergence by seven to eight days.

From flower initiation through physiological maturity, soybean development is controlled largely by day length. As the days become shorter, the plant moves through the reproductive stages more quickly. Because of this, soybeans are able to compensate for planting delays by reducing the length of time they remain in each of the reproductive growth stages. A good rule of thumb for Michigan conditions is that for every three days that planting is delayed, physiological maturity is delayed by only one day. Producers can use this information to estimate when their late-planted beans will reach physiological maturity.

Based on the information previously presented, the vast majority of the 2009 Michigan soybean crop will mature prior to a normally occurring killing frost. However, fields that were planted in low-lying areas, planted after the last recommended dates or planted to varieties that are not adapted to the growing area may be at risk.

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