Foliar diseases inhibit grain filling by reducing photosynthesis, reducing translocation of photosynthate and increasing respiration of the plant. This results in smaller grain which leads to increased screenings and lower grain yield. Less commonly, foliar diseases can reduce the number of kernels per spike if disease development occurs early in the season.
In the United Kingdom (UK) around 75 per cent of grain filling occurs within the first 4-6 weeks after head emergence. It is during this period that it is most important to minimise the severity of disease on the top three leaves as they contribute the most photosynthate to grain filling. However, in Australia, Bowring and Fettell (2011) found that responses to foliar fungicide applied to keep the flag leaf green after anthesis (the flowering period of a plant following the opening of the flower bud) may be smaller than expected in the UK, particular if there is any post anthesis stress, (Figure 2.1).
Foliar Diseases of Cereals
Factors Effecting Disease Damage