Knowing the stages of development of a crop is critical in many management decisions that growers make. They are represented on a scale from 10 to 92. For example, in some countries, nitrogen and herbicide applications must be completed during the tillering stage. In France, the recommendation for the first nitrogen application on wheat is 6 weeks before Z30, with the second application on Z30. Wheat growth regulators are typically applied at Z30. Disease control is most critical in the stem extension and heading stage (Z31, Z32, Z35), in particular as soon as the flag leaf is out (Z37). The crop is also more sensitive to heat or frost at some stages than others (for example, during the meiosis stage the crop is very sensitive to low temperature). Knowing the growth stage of the crop when checking for problems is essential for deciding which control measures should be followed.
Examples of typical stages
during tillering
Z10 : one leave
Z21 : tillering begins
during stem extension
Z30 : ear is one centimeter long in wheat
Z31 : first node visible
Z32 : second node visible
Z37 : flag leaf
during heading
Z55 : the head is 1/2 emerged.
during ripening
Z92, grains are ripe
Another cereal development scale is the Feekes one.
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