Effects of diseases on the growth and yield of spring linseed (Linum usitatissimum ), 1988-1998

In spring linseed field experiments with fungicides at Rothamsted from 1988 to 1998, substantial yield losses associated with diseases occurred in three years and slight losses could be associated with diseases in other years. These yield losses were related to decreases in yield components (thousand grain weights and number of capsules). Leaf browning was observed each year and percentage leaf area with browning was the disease factor most consistently related to yield losses tin five years). Yield loss relationships for these five years suggested that for each 10% increase in percentage leaf area with browning there was a yield loss of 0.10 to 0.18 t ha(-1). Stem browning, lesions on capsules and powdery mildew were associated with yield losses in two years, three years and one year, respectively. Yield losses were greatest in years when the period of flowering and early capsule development in June and July was wetter than average, the predominant disease was grey mould (Botrytis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola) was most important in 1997 and 1998. Observed yield losses were small in hot, dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae) were the predominant diseases.