ALBERT

Description: SummaryEight forage rape cultivars were grown in replicated trials in 1980, 1981 and 1982; the plots were either inoculated to promote early infection with powdery mildew (Erysiphe cruciferarum) or they received one application of fiuotrimazole (in 1980) or triadimefon (in 1981 and 1982) to control mildew.Mildew infections first appeared during August and increased rapidly during September to give highly significant differences between cultivars for the percentage leaf area infected in October; cv. Lair had the least mildew and cvs Samo, Early Giant, Bishop and Winfred were most severely infected. Regression analyses were used to investigate the increase in mildew over time in 1980 and 1981. No clear pattern of disease development was evident in 1980, but in 1981 the increase in mildew was predominantly linear and in untreated plots the greatest increase occurred in cvs Winfred, Samo and Bishop and the least in cv. Lair. Mildew was reduced in each year (P 〈 0·001) on fungicide treated plots and the mean fresh weight yield increase of 4·61 t/ha from treated plots was attributed mainly to the control of E. cruciferarum.Fungicide treatment had little effect on % organic matter (OM), % digestible organic matter (DOMD) or concentration of thiocyanate ion (SCN-); both % nitrogen (N) and concentration of S-methyl cysteine sulphoxide (SMCO) were reduced in fungicide-treated plots in 1981, and N was also reduced in 1982. The mean concentration of SCN- from treated and untreated plots over 3 years was least in cv. Samo (14·90 mg/100 g D.M.) and greatest in cv. Lair (22·15 mg/100 g D.M.). The response in yield and quality factors to fungicide treatment is discussed in relation to the control of powdery mildew and other, possibly phytotonic, effects.