When to swath after frost

In the past few days some regions, particularly in central Alberta, have experienced some light frosts.  Producers are asking if these frosts caused damage and whether they should be swathing right away or waiting to let the crop mature further. Below are some things to consider when making this decision, followed by a link to a fact sheet with more details on assessing standing fields following fall frost.

Scout, don’t swath. Given that in most affected regions temperatures did not dip below minus 2 C, damage is likely to be minor meaning swathing prematurely may do more harm than good. However, it is important to get out there and check crops to ensure damage is not greater than expected. If plants are severely damaged the pods will often take on a white, wilted appearance. This is a sign that pods are desiccating which will quickly lead to pod shatter and pod drop, especially with warm sunny afternoons. If pods are desiccating rapidly, swathing right away will preserve as much yield as possible.

If pods do not appear to be severely damaged, then continue monitoring rather than swathing right away. You may see some speckling on the stem and pods, but much of the seed inside will continue to mature as long as the plant is still alive. If no wilting, leave the crop standing and check daily.

What to look with daily monitoring:
—If the majority of the seeds remain turgid, delay swathing to allow for further seed maturity. Swathing assessment will be similar to an undamaged crop, but focus on the healthy seeds to monitor for firmness and seed color change.
—If the pods begin to desiccate, swath during periods of dew or high humidity to reduce the amount of pod shelling and pod drop.

Why wait? The amount of frost damage depends on various factors including crop stage, degree and length of frost, relative humidity, and presence of rain or dew. In many cases, a light frost will damage the outside of pods but seeds can continue to mature — increasing yield and quality — if the crop is left standing. 
Click here for more information on assessing crops following fall frost.