The effects of fungicides on rate and duration of grain filling in winter wheat in relation to maintenance of flag leaf green area

Three field experiments were conducted on sandy-loam soils comparing the effects of triazole, strobilurin and oxazolidinedione fungicides applied at flag leaf emergence and again at ear emergence to wheat between 1998 and 2000. Cultivars Hereward and Consort were included in all 3 years, Cockpit in 1999 and 2000 and Charger in 1999. Foliar disease, green area of the flag leaf, grain weight and moisture content were assessed weekly during grain filling and senescence. Grain yield, 1000 grain weight (TGW) and specific weights were measured at harvest maturity. Septoria tritici was the dominant disease in all cultivars except Cockpit, where Puccinia striiformis caused most damage. Consort was more affected than Hereward by S. tritici in all years. Effects of fungicides on disease control were usually reflected in green flag leaf area duration (GFLAD), with large gains in Consort and Cockpit. In 2000, however, fungicides increased GFLAD of Hereward and Consort by similar amounts. Apical grains had smaller water content than medially placed grains. Maximum water content was positively influenced by fungicides where significant disease was controlled before maximum grain weight had been attained. Grain weight in Hereward was less affected than other cultivars by fungicides in both positions. Grain filling rates varied between cultivar and ear position by inconsistent and small amounts, but large and significant gains from fungicide treatment were made in grain filling periods. These varied from 0.16 days per day GFLAD in Hereward to 0.69 days per day GFLAD in Consort in apical grains in 2000. Gains in GFLAD were associated with increased yield, TGW and specific weight, but these relationships varied with cultivar. Increases in GFLAD by fungicide in Hereward in 2000 occurred much later relative to grain filling and thus after the time of maximum grain water content, resulting in smaller gains in filling duration, yield, TGW and specific weight than that seen in Consort. There was no evidence of differing relationships between GFLAD and yield for the different fungicide groups used in these experiments.