Weather
Heat stress in wheat, cotton, rice and maize
Heat stress means temperatures above the critical level for a given crop. The main damage is not to leaves but to flowering: pollen becomes sterile, and buds and young bolls drop. A field can stay green while the yield is already lost, because losses depend on how many grains and bolls set.
Crops: Wheat, Cotton, Rice, Maize
When it is dangerous
The most sensitive window is budding and flowering: pollen sterility cannot be reversed, and wheat is most sensitive 2–3 days before flowering. During grain fill, heat speeds up ripening and leaves shrivelled grain. Winter wheat is hit in spring at flowering; cotton, rice and maize during summer heat waves.
Causes
- A heat wave above the crop's critical temperature
- Heat combined with a shortage of soil water
- Hot dry wind (garmsel)
- Too little irrigation during hot spells
Signs on the field
- Leaves curl and wilt around midday
- Buds and young bolls drop
- Empty or partly empty wheat ears
- Early ripening and shrivelled grain
How ClusterOS notices it
Weather is the main signal: ClusterOS compares air temperature with each crop's threshold and takes the field's growth stage into account. Satellites cannot see early canopy overheating, and pollen sterility leaves the plant green. Sentinel-2 optical imagery only shows late effects such as an early end of the season, and clear images can be 10–20 days apart. Only a field count of empty spikelets and dropped bolls confirms the loss.
What to do
- Avoid water shortage during heat: irrigation partly cools the crop through transpiration
- Log irrigations so you can tell pure heat stress from heat combined with drought
- After a heat wave at flowering, inspect the field: count empty spikelets and dropped buds and bolls
- Record growth stage dates accurately – the danger of heat depends on them
Questions
At what temperature does heat damage cotton?
Published data show that when the daily mean temperature rises above 32 °C, cotton retains far fewer bolls and sheds them within 3–5 days. Cotton pollen germinates best around 32 °C and fails completely around 37 °C. These are global literature values and need local calibration.
How is heat stress different from drought?
Heat damages the crop even when the soil has enough water, and the danger is tightly tied to the growth stage. Irrigation partly cools plants but does not protect flowering at extreme temperatures. Heat and drought often come together, and then they act as a combined stress.
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
- Luo et al. 2023, Plant Communications
- Tashiro T., Wardlaw I.F. 1990; Prasad et al., DOI: 10.1071/FP14061
- Burke et al. 1988; Conaty et al. 2012
- Sommer R. et al. 2013, DOI: 10.1016/j.agee.2013.06.011