Crop Phenology - The Growth Stages

The most important factor in the success of a fungicide application is timing; not in relation to the day of the year, but in relation to disease development and crop growth. A good understanding of the decimal code of growth stages (GS), the physiology of the plant at each stage and disease development will all help for sound management decision making, (Table 2.5). Three plant growth stages are particularly important for fungicide application decision-making. At GS 32 two nodes are detectable and leaf 3 is emerging. At GS 39 the flag leaf has completely emerged, and at GS 58 the head is fully emerged, (Figure 2.1). A fungicide application at each of these growth stages should offer excellent protection of the top 3 leaves throughout the grain filling period, but this is rarely economical. It is generally accepted that a single application is best applied at GS 39, depending on the target disease.

Figure 2.1 Contribution of photosynthate to grain filling for wheat and barley. (Illustration by Kylie Fowler)

Table 2.5 The decimal code of cereal growth stages (Zadoks et al., 1974)

DESCRIPTION GROWTH STAGE
1. Seedling Growth  
1st leaf unfolded 11
2nd leaf unfolded 12
3-9 leaves unfolded 13-19
2. Tillering  
Main shoot only 20
Main shoot + 1 tiller 21
Main shoot + 2 tillers 22
Main shoot + 9 or more tillers 29
3. Stem Elongation  
Pseudostem1 30
1st node detectable 31
2nd node detectable 32
3rd to 6th node detectable 33-36
Flag leaf just visible 37
Flag leaf collar visible 39
4. Booting  
Flag leaf sheath extending 41
Boot just visibly swollen 43
Boot swollen 45
Flag leaf sheath opening 47
1st awns visible 49
5. Head Emergence  
1st spikelet of head visible 51
1/4 head emerged 53
1/2 head emerged 55
3/4 head emerged 57
Head emergence complete 59
6. Anthesis (flowering)  
Anthesis beginning 61
Anthesis half-way 65
Anthesis complete 69
7. Milk Development  
Caryopsis water ripe2 71
Early milk 73
Medium milk 75
Late milk 77
8. Dough Development  
Early dough 83
Soft dough 85
Hard dough 87
9. Ripening  
Caryopsis hard 91
Caryopsis loosening in daytime 93

1Pseudostem – a false stem formed of the swollen leaf bases

2 Caryopsis – a dry one-seeded fruit in which the ovary wall is united with the seed coat, typical of grasses and cereals

Factors Effecting Disease Damage

The Integrated Approach to Disease Management