With the forecasted cooler overnight temperatures, here is a refresher on the potential impact spring frost can have on winter wheat crops in Manitoba. (Hopefully, we won’t have a need for this post!). Currently, winter wheat acres range in development from tillering to stem elongation.
For winter wheat at tillering stage, plants can withstand very low temperatures for a period of time (-11°C for less than 2 hours). Frost damaged winter wheat at this stage will have leaf chlorosis and necrotic leaf tips. However, the effect on yield will be slight.
For winter wheat at jointing stage (stem elongation), plants can tolerate temperatures of -4°C for less than 2 hours. Frost injury symptoms could include a dead leaf appearing in the whorl if the growing point was damaged, leaf yellowing or burning, or splitting or bending of the lower stem. The impact to yield can range from moderate to severe, and lodging can also occur later in the season if stems were damaged.
For winter wheat at the boot stage, plants can tolerate temperatures of -2°C for less than 2 hours. Frost injury symptoms in winter wheat (or even fall rye) can include spikes being trapped inside the boot and they may not emerge normally, spikes may emerge but may remain yellow or even white (sometimes only portions of the head may be impacted), awns may be twisted and you may see floret sterility resulting in poor kernel set and low grain yield.
In 2012, we did see winter wheat crops impacted by frost. A frost event occurred May 30 when some winter wheat acres were at the early flag emergence stage. When the spikes started to emerge, injury symptoms were noted. In the photo below (taken by Ingrid Kristjanson, MAFRD), you will note frost injury symptoms of twisted awns and incomplete kernel set.
In Manitoba Agriculture’s June 3, 2015 webinar (available on YouTube at http://youtu.be/UDa3uWMmZzg), I covered some of the basics of frost injury symptoms in winter cereal crops and what to look for in terms of recovery.
For more information on frost damage in winter cereals and other crop types, please refer to Manitoba Agriculture’s Spring Frost Damage Bulletin.
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture