Our current winter wheat crop condition for Ellis and Barton County has been pretty favorable due to the precipitation events last fall and this winter. There are always exceptions to this, where the crop did not emerge until later, due to when the crop was planted, when and how much moisture was received.
No surprise to anyone, that our winter has been warmer than average, my wife would argue that fact with me, but the weather data does not lie. Growing degree days (GDD) is a measure used to estimate the growth and development of a certain crop during the growing season. According to Kansas Mesonet weather data the GDD are well ahead of the normal averages for our Kansas wheat crop.
Last week Kansas experienced a cold front that sent temperatures well below freezing. What kind of impact can that have on our wheat crop in this area. Well like so many things, it depends. Factors that influence the potential for freeze injury to wheat include primarily:
• Growth stage of the crop
• Air temperatures
• Duration of cold temperatures
• Soil temperatures
• Snow cover
Other factors, such as position in the landscape and the presence of residue covering the soil surface, might also impact the extent of freeze damage within a field. “The challenge is integrating all these factors into a reasonable estimate of freeze injury”, according to Romulo Lollato, K-State Wheat Specialist.
Soil temperatures can help buffer freezing air temperatures if the growing point is below ground or near the soil surface. However, its buffering capacity decreases as the crop develops and the growing point moves above the soil surface. Thus, we can expect a positive effect from soil temperatures in the majority of the state since soil temperatures did not reach levels below 35 degrees F, with exception of southeast where the crop is further along and the growing point is well into the canopy.
For fields that have not jointed yet, the crop can generally withstand temperatures of 15-20°F fairly well, especially if the growing point is still below ground. Kansas Mesonet data indicates that temperatures fell below this threshold, reaching as low as about 10°F in parts of northwest Kansas.
If the growing point is already above ground (first joint visible), wheat can sustain temperatures down to about 24 degrees F for a few hours. Minimum temperatures below 24°F for extended periods of time increase the risk of crop injury. Information from the K-State Mesonet indicates that air temperatures were around this 24°F threshold in most of central and north-central Kansas; however, they dipped below the threshold for as many as 17-21 hours in southwest Kansas, which can cause damage to fields at the first node of development or more advanced stages.
Based on the wheat growth stage, temperature and duration of temperature. Romulo Lollato says “we estimate that parts of southwest Kansas would be more exposed to the potential freeze damage”, given that the crop is relatively advanced (at or past jointing) and was met with many hours of air temperatures below 24°F, with lowest temperatures reaching 13°F.
In the remainder of the state, temperatures needed to cause damage at the observed crop stages were borderline, and therefore, we expect that only more advanced fields could sustain freeze damage.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at scampbel@ksu.edu or call the Hays office, 785-628-9430.
