Growth scales are a means of quantifying the growth stage of a crop in a standardised way and are useful when:
- There is a need to identify a particular growth stage for the safe application of a herbicide or fungicide.
- Communicating the growth stage of a crop to advisers or research services when seeking advice on the development of diseases or nutrient deficiencies.
- Sampling plant tissues for nutrient analysis.
The Zadok's growth scale is based on ten principal cereal growth stages:
- 0 - Germination
- 1 - Seeding growth
- 2 - Tillering
- 3 - Stem elongation
- 4 - Booting
- 5 - Awn emergence
- 6 - Flowering (anthesis)
- 7 - Milk development
- 8 - Dough development
- 9 - Ripening
Each primary growth stage is divided into 10 secondary stages, extending the scale from 00 to 99. The early growth stages (1, 2 and 3) are referred to most frequently. The scale does not run chronologically from Z00 to Z99. For example, when the crop reaches three fully unfolded leaves (Z13) it begins to tiller (Z20), before it has completed 4, 5 or 6 fully unfolded leaves (Z14, 15, 16).
0 - Germination
- 00 - Dry seed
- 01 - Start of water absorption
- 03 - Seed fully swollen
- 05 - First root emerged from seed
- 07 - Coleoptile emerged from seed
- 09 - First green leaf just at tip of coleoptile
1 - Seedling growth
Count leaves on main stem only. Fully emerged = ligule visible. Subdivide the score by rating the emergence of the youngest leaf in tenths. For example, 12.4 = two emerged leaves plus the youngest leaf at 4/10 emerged.
- 10 - First leaf through coleoptile
- 11 - First leaf emerged
- 12 - Two leaves emerged
- 13 - Three leaves emerged
- 14 - Four leaves emerged
- 15 - Five leaves emerged
- 16 - Six leaves emerbed
- 17 - Seven leaves emerged
- 18 - Eight leaves emerged
- 19 - Nine or more leaves emerged
2 - Tillering
Count visible tillers on main stem; that is, the number of side shoots with a leaf blade merging between a leaf sheath and the main stem.
- 20 - Main stem only
- 21 - Main stem and one tiller
- 22 - Main stem and two tillers
- 23 - Main stem and three tillers
- 24 - Main stem and four tillers
- 25 - Main stem and five tillers
- 26 - Main stem and six tillers
- 27 - Main stem and seven tillers
- 28 - Main stem and eight tillers
- 29 - Main stem and nine or more tillers