Weather
Winterkill of winter wheat: frost, ice crust and smothering
Winter crops die in winter for three different reasons: hard frost kills the tillering node, an ice crust cuts off air, and deep snow on unfrozen soil smothers the crop. Losses range from a thinned stand to complete loss of the field and resowing with spring crops.
Crops: Wheat, Barley, Rye, Alfalfa
When it is dangerous
The most dangerous time is winter dormancy and thaws. Frost hardiness is built in autumn during tillering, and weak or overgrown stands go into winter unprepared. A week of thaw at about +10 °C noticeably reduces hardiness, and a sharp freeze after a thaw can cost up to 90% of the yield.
Causes
- Hard frost with little snow cover
- Thaw, rain and frost in a row, forming an ice crust
- Long-lasting deep snow on unfrozen soil
- Loss of hardiness during a long thaw
- Meltwater standing in low spots
Signs on the field
- A thin or empty stand in spring
- A browned tillering node when the plant is cut open
- Suffocated shoots with a fermented smell under the ice
- Pale, exhausted plants with mould after the snow melts
How ClusterOS notices it
In winter ClusterOS relies on weather: soil temperature, snow depth and the sequence of thaws and frosts. Nobody measures temperature directly at the tillering node, so the 7–28 cm soil layer is used as a proxy, not a measurement. Sentinel-1 radar sees through clouds and helps spot ice, but not reliably. Satellites cannot see the crop under snow, so losses show up only in spring on Sentinel-2 imagery, and the most accurate survival check is an agronomist regrowing plant samples in the warm.
What to do
- Sow on time and at the right depth and retain snow – this lowers the risk of winterkill
- Do not sow too densely, cut autumn nitrogen and treat seed against snow mould
- Drain meltwater from low spots and level the field
- Regrow tillering-node samples in the warm – it is the only direct way to see how many plants survived
Questions
At what temperature does winter wheat freeze to death?
The critical temperature at the tillering node of winter wheat is about −18 °C, down to −22 °C for the hardiest varieties, and a more cautious planning limit is −16 °C. Winter barley is less hardy (−13…−16 °C), winter rye hardier (−20…−24 °C). This is the temperature at the depth of the tillering node, not in the air.
How long can winter crops survive under an ice crust?
Estimates vary widely. Early studies gave less than 7 days of survival under solid ice, trials on modern varieties 18–33 days. Alfalfa and perennial grasses die under a crust in about 50 days.
Learn about this risk on your fields before it becomes a loss
We will show ClusterOS on your own fields: history since 2019, crop stage and all 24 risks.
Other risks in «Weather»
Scientific basis
- Andrews C.J., Pomeroy M.K. 1979, Plant Physiology 64:120, DOI: 10.1104/pp.64.1.120
- Skarratt D. et al. 2024, Canadian Journal of Plant Science, DOI: 10.1139/cjps-2023-0143
- Gusta L.V., Fowler D.B. 1976, Canadian Journal of Plant Science, DOI: 10.4141/cjps76-107
- Aase J.K., Siddoway F.H. 1979, Soil Science Society of America Journal