A Midwinter's Thaw Nightmare?

While the title of this blog post is probably not the best antonym for Shakespeare's 'A Midsummer Night's Dream', the weather fairies are creating some intrigue and possible mischief for the state's winter annuals and perennials with this extended midwinter thaw that is breaking records up and down the State. Before I can argue that winter wheat and winter rye crops are NOT doomed, I'll try to explain how winter wheat and winter rye get through the winter.  

Winter wheat and winter rye both have a vernalization requirement. Vernalization is the accumulation of a set number of cold units.  Cold units are accumulated when soil and ambient temperatures are roughly between 32 and 50 degrees Fahrenheit. This requirement is an evolutionary adaptation to delay the transition from vegetative growth to reproductive growth even if the temperatures are (temporarily) very favorable: As long as the vernalization requirement is not met, the growing point will stay below ground and is partially protected from freezing temperatures. The vernalization genes impart low-temperature tolerance that allows the crop to go dormant once the temperatures fall below freezing. This dormancy is not a static condition and wanes as the crown ages throughout the winter.  

Winter wheat and winter rye are also photoperiod sensitive.  Both species are generally thought of as long-day (LD) photoperiod sensitive. This means that the days have to get to a certain minimum length before the plant can transition from vegetative growth to reproductive growth. This too is an evolutionary adaptation to delay the transition from vegetative growth to reproductive growth even if the temperatures are (temporarily) very favorable.

So....where are we now?  

It is early February and both soil temperatures and ambient temperatures are warm enough for winter wheat and winter rye to start growing again. The growing conditions last fall were nice enough, long enough that all but extremely late-seeded fields of winter wheat and winter rye have met their vernalization requirement.  However, the daylengths are not nearly long enough to trigger the transition to reproductive growth. Therefore, even if the crop comes out of its low-temperature slumber and resumes growth the growing point will remain below the soil surface. The crop will simply develop more tillers and remain somewhat protected from the most extreme temperatures.

When Jack Frost returns, photosynthesis and growth once again halt. Unfortunately, the aging crowns never reach the same level of low-temperature tolerance they had before breaking dormancy. Snow cover, however, can offset the lowered ability to tolerate the most extreme temperatures. It's why I prefer no-till production systems for winter cereals as standing stubble greatly improves snow-trapping potential and the longevity of the snowpack once it has been trapped.

Luckily, March is generally the month with the most snowfall, and the parts of the state that are now enjoying the mildest temperatures also get most of that snow. 

Bottomline: Nothing is lost yet - Winter wheat in Kansas and Nebraska goes through this almost every year and it is said that the winter wheat in those two states has nine lives. Our winter wheat and winter rye are still on their first.