While we continue to have no control over the weather, we have access to near- and longer-term temperature and precipitation ‘normals’ and forecasts that our forebears did not. Knowledge about what has happened in the near past, freeze probabilities, current and forecasted air temperature and precipitation and the earliest and latest crop insurance planting dates can help crop producers to better gauge the risk of either planting on a particular day or holding off. Oftentimes decisions hinge on field conditions, just how many acres need to be planted and an individual farmer’s risk tolerance.
What does the data tell us about final frost dates?
The National Oceanic and Atmospheric Administration (NOAA) uses the 1981 through 2010 calendar years to calculate the probability of a later 28 degree freeze than a given date at a given location. Their summary for the Northwest Research and Outreach Center in Crookston lists that there is a 90 percent probability of a 28 degree frost occurring later than April 16, a 70 percent probability of frost occurring after April 25, a 50% probability after April 30, a 30% probability after May 6 and a 10% probability after May 16. Similar data for other northwest Minnesota locations can be found in the table below.Table. Probabilities of observing a temperature as cold or colder than 28 degrees later than the dates listed at each location (based on 1981-2010 normal temperatures; source: NOAA: National Centers for Environmental Information)
Location
|
Probability of 28 degrees on a later date
than listed
|
||||
0.10
|
0.30
|
0.50
|
0.70
|
0.90
|
|
Ada
|
5/17
|
5/07
|
5/01
|
4/26
|
4/16
|
Agassiz
Refuge
|
5/13
|
5/04
|
4/29
|
4/23
|
4/15
|
Argyle
|
5/21
|
5/12
|
5/04
|
4/29
|
4/19
|
Crookston
|
5/16
|
5/06
|
4/30
|
4/25
|
4/16
|
Hallock
|
5/20
|
5/12
|
5/05
|
4/29
|
4/20
|
Roseau
|
5/23
|
5/13
|
5/05
|
4/30
|
4/22
|
Thief
River Falls
|
5/22
|
5/12
|
5/06
|
4/29
|
4/21
|
Why it matters: sensitivity of germinating seeds to cool temperatures.
Seed germination and seedling growth is retarded when soil temperatures are lower than 50 degrees. Slowed germination rates and seedling growth and emergence can put the crop at risk for a variety of reasons.Imbibition is the passive absorption of water from the seed’s immediate environment. When temperatures are too cold, seedlings can be damaged by a phenomenon called ‘imbibitional chilling injury’ that is caused by poor cell elasticity and resultant cell damage. A detailed explanation of imbibitional chilling injury can be found on the website run by Purdue University’s Dr. Bob Nielsen.
Sensitivity of seedlings to frost.
The sugars and salts that are inside plant cells mean that plant cells don’t freeze at 32 degrees but rather can survive temperatures dips even a couple of degrees below 32 for short periods of time. It is when temperatures reach about 28 degrees that ice crystals can form inside of cells, causing cell membranes to rupture and cell contents to spill out. With their growing-point above ground emerged soybean seedlings are at particular risk of injury or death due to frost. Corn seedlings, with their growing-point remaining below ground until approximately the six-leaf growth stage, remain a bit more protected from these temporary temperature drops. While some injury can occur setting back crop development (Figure), short-term low temperatures are less likely to result in plant death in corn. A notable exception is when there are dry soil conditions as water tends to slow temperature changes. |
| Figure. Corn seedling that was damaged by frost. Note that the above-ground tissue was killed and the below-ground tissue was protected and insulated by the soil. |
Knowledge of temperature ‘normals’, short- and longer-term forecasts and field-specific soil temperature measurements can help crop producers to minimize temperature-related risks.
Early and Final Planting Dates.
The USDA Risk Management Agency determines early and final planting dates for corn and soybean for crop insurance purposes. In Minnesota the earliest planting date is April 21 and the latest planting date is June 10. The earliest planting date for Minnesota corn is April 11 and the latest planting date for the majority of the southern two-thirds of the state is May 31 and for the northern third is May 25.References.
Nielsen, RL (Bob). 2015. Corkscrewed Mesocotyls & Failed Corn Emergence. Corny News Network, Purdue Univ. Online at https://www.agry.purdue.edu/ext/corn/news/timeless/Corkscrews.html [URL accessed April 2019].
NOAA. National Centers for Environmental Information. Last Spring Freeze. [URL accessed April 2019].
