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Early fall frost and soybean

Early frost can affect soybean yield and quality. However, the severity of frost damage greatly varies based on local climate conditions, topographical features, soybean management and growth conditions.

field of green plants with some plants looking slightly dry and wilted.
Figure 1: The open canopy (left) allowed frost to penetrate more deeply in the more mature soybeans compared to the less mature soybeans (right).

Factors affecting damage

Dense and lush soybean canopies tend to fend off severe freezes by holding heat within the canopy. Open canopies, on the other hand, tend to allow the cold air to access the lower canopy (Figure 1).

Late planting, soybean cyst nematode (SCN), iron deficiency chlorosis (IDC) and/or some conventional herbicides tend to promote open canopies. It’s likely these fields will be damaged more by frost than less stressed fields.

Likewise, soybeans nearing maturity tend to see deeper frost damage due to dropped leaves and open canopies. However, injury in the form of reduced yields is greatly reduced if frost hits as soybeans near the R7 growth stage (one mature colored pod on the main stem).

Estimating yield loss

Due to the variable nature of frost, yield loss estimates are quite difficult to come by. Yield and quality reductions depend on the crop stage when frost occurs and the frost’s severity.

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Frost effects on crop quality

Arresting soybean development late in seed fill tends to reduce yield because oil stops getting deposited in the seed. Oftentimes, frost-damaged seed is small, flat and green, with normal protein but low oil concentrations.

Handling frost-damaged grain

Mixing severely frosted grain with normal grain can potentially cause complications for the producer, from storage through marketing.

Grain from damaged areas can resist field dry-down and maintain excessive moisture levels through harvest. In addition, elevators may refuse loads with green soybean, or impose stiff dockages.

Isolate frost-damaged areas (especially late planted and/or drowned-out areas) and harvest them after the unaffected areas. While this can add logistical challenges for large operations, it could reduce the risks of storing damaged grain and will isolate potential dockages to individual loads rather than whole bins.

How to handle frosted corn and soybean crops

Seth L. Naeve, Extension agronomist; Jeff Coulter, Extension agronomist; Dave Nicolai, Extension educator and Phyllis Bongard, Extension communications specialist

Reviewed in 2018

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