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
3 - Stem elongation
Generally count swollen nodes that can be felt on the main stem. Report if dissection is used.
- 30 - Pseudostem (youngest leaf sheath erection)
- 31 - First node detectable
- 32 - Second node detectable
- 33 - Third node detectable
- 34 - Fouth node detectable
- 35 - Fifth node detectable
- 36 - Sixth node detectable
- 37 - Flag leaf just visible
- 39 - Flag leaf ligule just visible
4 - Booting
Score the appearance of the sheath of the flag leaf.
- 41 - Flag leaf sheath extending
- 43 - Boots just visible swollen
- 45 - Boots swollen
- 47 - Flag leaf sheath opening
- 49 - First awns visible
5 - Ear emergence from boot
- 51 - Tip of ear just visible
- 53 - Ear quarter emerged
- 55 - Ear half emerged
- 57 - Ear three quarters emerged
- 59 - Ear emergence complete
6 - Anthesis (flowering)
Generally scored by noting hte presence of emerged anthers.
- 61 - Beginning of anthesis (few anthers at middle of ear)
- 65 - Anthesis half-way (anthers occurring half way to tip and base of ear)
- 69 - Anthesis complete
7 - Milk development
Score starch development in the watery kernel.
- 71 - Kernel water ripe (no starch)
- 73 - Early milk
- 75 - Medium milk
- 77 - Late milk
8 - Dough development
Kernel no longer watery but still soft and dough-like.
- 83 - Early dough
- 85 - Soft dough
- 87 - Hard dough
9 - Ripening
- 91 - Grain hard, difficult to divide
- 92 - Grain hard, not dented by thumbnail
- 93 - Grain loosening in daytime
- 94 - Over-ripe straw dead and collapsing
- 95 - Seed dormant
- 96 - Viable seed giving 50% germination
- 97 - Seed not dormant
- 98 - Secondary dormancy induced
- 99 - Secondary dormancy lost