Surprise....(and not in a good way)

Below is a picture of a spring wheat field in west-central Minnesota with rye plants that have started to head, scattered throughout.  The grower was a bit surprised to find rye already heading in his field. Worried about the spring wheat being contaminated with rye and not making grade, he contacted his seed dealer.  

The rye was most likely but inadvertently seeded when the fertilizer was applied this spring, given that the rye plants that are heading out are not in the spring wheat rows and in a field that has not had a winter rye cover crop previously. 

But why is it already heading?

The difference between a spring growth habit and a winter growth habit in cereals is the vernalization requirement that winter wheat and winter rye have and that spring wheat or spring barley lack. Vernalization is the need for the accumulation of a set amount of cold units that the seedling needs to accumulate after emerging to trigger the transition from vegetative to reproductive growth.  During the vegetative growth stage, the plant only produces leaves and tillers, and the growing points stay below the soil surface. Not until the vernalization requirement has been met will daylength and/or heat units allow stem elongation to start and growing points to switch from making leaves to developing a head. 

The optimum temperatures to accumulate cold units for winter rye are between 34F and 45F.  No cold units are accumulated below freezing or when temperatures are above 59F. Winter rye and winter wheat varieties, depending on the genetic makeup,  need 8 to 10 weeks to accumulate enough cold units. The expectation, therefore, is that when you seed a winter rye or winter wheat variety in the spring, you just see a lush green lawn. 

Not this spring - The prolonged stretch of cooler-than-normal spring weather has apparently allowed this winter rye seed to meet its vernalization requirement.  Winter rye's very strong daylength response did the rest and made it already head out.  

Now what? 

Controlling volunteer or feral rye is a perennial problem in winter wheat across the Great Plains and the PNW. This article, authored by Drew Lyon, Judit Barroso, and Joan Campbell at Washington State University, sums up the challenges well, and an integrated approach is key to avoiding a rapid escalation of the problem.  In the field in question, only roguing or a glyphosate rope wick are the options left on the table. 

Photo 1 - Volunteer winter rye in a field of spring wheat near Benson, MN.