448 



The Control of Onion Smut. 



[Aug., 



The best seed treatments, therefore, were : — soaking in water 

 for two days; soaking in 10 per cent, sulphuric acid for one 

 hour; and dusting with 0.28 grammes of paraform. 



The best soil treatments were : — hme, salt, bleaching powder 

 and soot. 



The sowings were made so late (Sept. 2nd) that it is certain 

 that these figures include plants killed out by the cold weather 

 as well as those killed by Smut, but that they roughly represent 

 the mortality due to Smut is shown by the fact that adjoining 

 plots which were sown earlier had 90 per cent, of the crop 

 diseased. 



Probability of Death Resulting from Infection. — To test 

 whether infected plants are able to " grow out " of the disease, 

 45 plants affected with Smut were marked and kept under 

 observation. The fact that 42 of these plants succumbed shows 

 that the chances of an infected plant surviving are somewhat 

 remote. 



Soil Treatment, 1920.— On May, 6th, 1920, a trial, was laid 

 down similar to the autumn trial of 1919, with the addition of 

 a plot treated with 2 lb. of carbon bi-sulphide worked into the 

 land a fortnight before sowing. 



In each case an area of 7 yd. by 1 yd. constituted a plot. 

 Counts were only made along the untreated seeds rows with a 

 view of determining the effect of the soil treatments. 

 Taking 100 as representing a full crop for one yard : — 



Plot (1) Jib. of paraform worked into the land a fortnight before 

 sowing gave 60 healthy plants. 



Plot (2) 2 lb. of bleaching powder applied as in plot (1) gave healthy 

 plants. 



Plot (3) 2 lb. of salt applied as in plot (1) gave 10 healthy plants. 

 Plot (4) 21b. of soot applied as in plot (1) gave 30 healthy plants. 

 Plot (5) 2 lb. each of soot and salt applied as in plot (1) gave 2 healthy 

 plants. 



Plot (6) Untreated Soil gave 15 healthy plants (control). 



Plot (7) 2 lb. of lime applied as in plot (1) gave 15 healthy plants. 



Plot (8) ] lb. of nitrate of soda worked into the land a few days 

 before sowing, followed by a similiar application a few days after sowing, 

 gave 10 healthy plants. 



Plot (9) Top 3 in. of soil removed, burned and replaced, gave 70 

 healthy plants. 



Plot (10) 21b. of carbon bi-sulphide applied as in plot (1) gave 50 

 healthy plants. 



From these results it Avonld appear that th'^ best soil treat- 

 ment was burning ; the next best was paraform ; and the third 

 best carbon bi-sulphide. 



