The late spring and cool summer has prompted a great deal of discussion on the maturity dates and consequently the harvest time of our area crops.
"Growing degree days" is a tool that has been developed by agriculture research scientists to estimate the growth stage of a crop. Barley, corn, sunflower, canola and wheat are examples of crops that have growing degree day models. These growing degree days, or heat units, are calculated by subtracting the lower threshold temperature from the average daily air temperature. The lower growth limit will vary with plant species.
The North Dakota Agricultural Weather Network is a series of 67 weather stations located across the state of North Dakota. These stations accumulate weather data and can be used for applications such as determining growing degree days for a crop in a specific area. Farmers use this growing degree data for help in determining growth states for crops when spraying for pest control. This time of the year farmers can use the network to estimate when their crop will reach physiological maturity.
The maturity time of sunflowers this year is a concern because of the cool weather and the long season that is needed for them to develop. The Minot area as of Aug. 19 is at 1,755 growing degree days given a May 15 planting date. This is 263 growing degree days below normal. This time of the year the area accumulates 23 growing degree days per day. The average accumulation continues to drop as our average temperatures drop. With normal temperatures for the remaining portion of the growing season, it is estimated, depending on the hybrid, these sunflowers will not reach maturity until early October.
The average first frost in the Minot area is Sept. 18. Minot has a 50 percent probability of having temperatures as low as 28 degrees by Oct. 3. There is a 90 percent probability that there will be temperatures at 28 degrees by Oct. 17. The weather history can vary for each community in the area. For example, Kenmare has a 50 percent probability of having 28 degrees as early as Sept. 24.
Mike Rose is North Dakota State University Extension service agent for Ward County.