Incidence of take-all on wheat and barley on experimental plots at Woburn

Summary. Surveys were made in 1931, 1932 and 1933 of the incidence of take-all on wheat and barley grown in the continuous experiments at the Woburn Experimental Station. Ten random samples consisting of all the plants in two half-metre lengths separated by a metre and taken from adjacent rows were obtained from each plot. The numbers of clean and diseased plants, their tillers and yield of straw and of grain were determined for each sample. No manure had been applied since 1925-6 except to certain of the barley plots. There was little or no take-all on plots which had received ammonium sulphate alone, with minerals, or with 1?2 tons of lime, while the disease was present in most of the other plots. In general there was a higher percentage infection on wheat, reaching a maximum of 52.5 per cent, on one plot, than on barley in which the highest percentage infection on any plot was 16.2. Little or no take-all appeared on either wheat or barley in plots whose pH. was 5 or less, comparatively little at pH 5.1 and in general considerably more at higher pH values. In spite of considerable variation in infection at the same pH. values there was a general tendency for percentage infection to rise with pH in wheat, but this was not apparent in barley. The wheat plot 10 B which had received rape dust was exceptional in that though it had a pH. of 5.4 little infection appeared. The corresponding barley plot also had little infection but its pH. was only 5.1. No clear relationship between yield and incidence of take-all was found. In the three years in which observations were made take-all appeared to increase in wheat till 35 per cent, of the plants were infected and then to decrease. Two years' observations on barley suggest that the corresponding figure for this crop is about 10 per cent. The total number of plants obtained from all the wheat samples increased slightly from 1931 to 1932 and decreased by more than half in 1933. The average percentage of take-all increased considerably from 1931 to 1932 and remained about the same in 1933. The average loss in yield due to take-all in thirteen affected plots rose from 16 per cent, in 1931 to 20 per cent, in 1933, with a maximum loss in any plot of 42 per cent. A white mycelium belonging to an Agaric of the Cortinarius type was found frequently on the roots and basal parts of wheat and barley. In general it did not appear parasitic but there is some evidence that in certain plots it had become so, causing considerable loss in yield. Take-all was very much less on wheat grown in alternate years with green manure intervening than on the continuous wheat.