Zadoks Growth Scale is a standardised reference scale used to evaluate and measure the plant growth stage in cereals.
Accurate assessment of growth stage is important because the cereal plant’s response to herbicide, growth regulator or fertiliser application depends on its stage of development. The Zadoks (or Decimal) growth scale of cereals is recognised internationally for research, advisory work and farm practice. In Europe the decimal scale is already used in farming publications and the labeling of agrochemicals; and its use in Australia has been endorsed by the Australian Weeds Committee.
Zadoks Decimal Scale
The decimal growth scale is based on ten principal growth stages labeled 0 to 9. These sub-divide the cereal plant life cycle into 10 major stages:
- Seedling growth
- Stem elongation
- Ear emergence
- Milk development
- Dough development
Each primary growth stage is then sub-divided into 10 secondary stages extending the scale from 00 to 99 (see Growth Scale Table). Early growth stages of seedling growth (1) tillering (2) and stem elongation (3) – which are the most important commercially – are described exactly by counting the organs on the plant. For example, a “one-leaf” plant is scored as 11 and a “three-leaf” as 13. Similarly, one tiller is 21, four tillers 24, one node or joint detectable in the stem 31, and so on.
Growth scores are concurrent. Because more than one growth process is going on at the same time, for example leaves emerging and tillers forming, more than one growth score may apply at the same time. For example a plant may be scored as 17 (seven leaves on the main shoot), 24 (four tillers) and 31 (one node detectable). Another example is when drought affected plants flower before the head has fully emerged from the boot. Such a plant might be scored 53 (¼ inflorescence emerged) and 65 (flowering). Although confusing at first, the concurrent scores do accurately reflect the current growth stage of the plant.
Using the Scale
Use of the Decimal growth scale may appear to be an unwelcome complexity to add to the problems of managing a crop. Nevertheless, there are two vital reasons for introducing it:
- To improve and standardise communication between people in all sectors of agriculture. It is much more informative for the plant pathologist to know that the diseased crop was at growth stage 39- flag leaf ligule visible – than to be told that it was at “jointing”.
- More accurate description of growth stage is required as advice on crop management is increasingly given in terms of growth stage rather than calendar time. How much better is the advice available on herbicide tolerance when the growth stage is given as 24/31 rather than a vague description of “mid- to late tillering” or “seven weeks from sowing”.
Like all growth scales the Decimal scale includes certain conventions and requires some practice before the user becomes fully familiar with it. The Decimal scale is based on observation of an individual plant, not the general appearance of a crop. It therefore requires the user to either choose a plant as representative of the crop; or to sample the crop, score the chosen plants and determine the average growth stage. (Acknowledgment: This information was adapted from a Farmnote by M.W. Perry published by the Western Australian Department of Agriculture and the Victorian Department of Primary Industries).