While traveling in the eastern Dakotas last week, I saw a lot of spring wheat fields that were heading.

Isn’t this really early?

Why is it happening?

What does it mean for yields?

Jochum Wiersma, University of Minnesota Extension small-grains specialist, says he was getting calls about the same thing. Development of hard red spring wheat in the Northern Plains is — in absence of stressors like excess water or low fertility — mostly driven by temperature. It’s all about growing degree days, he says.

ON PACE: Wheat heads are appearing earlier in the season than the past few years due to warmer weather.

This year, growing degrees accumulated faster than last year. Although 2015 had lower maximum temperatures in the second half of May and the first half of June than either 2010 or 2016, the difference in daily minimum temperature is even more pronounced.

So what does this mean in terms of yield potential?

In general, a slower accumulation of growing degree days means higher yields, Wiersma says. Faster accumulation means lower yields.

“When the same number of heat units are accumulated, having them accumulated with a larger difference between the minimum and maximum daily temperatures is more advantageous, as long as the maximum temperatures doesn’t exceed 85 degrees F too long during the daytime,” he says.

The bottom line: The yield potential at this point is slightly lower than what it was in 2015, but similar to 2010, Wiersma says.

However, yield potential is not the same as actual yield and, the nighttime temperatures during the grain fill period will have significant impact on the final yields.

So watch the weather!