420 Summary of Agricultural Experiments, [aug. 



The results were disappointing, spraying- with liver of sulphur four 

 times during the season being the only treatment that seemed to have 

 any effect in reducing the number of affected plants, and that but a 

 slight one. The most striking results were from two plots where only 

 one row of plants, 3 feet apart, was planted, instead of three rows, as 

 on the other plots. This seems to show that there is far less chance 

 of infection when the plants are well isolated than when they are 

 crowded together, mutually shading each other, and having their 

 stalks surrounded with more or less moist stagnant air. Such wide 

 planting would not be practicable on a large scale, but less close plant- 

 ing than is sometimes seen may be desirable. A number of similar 

 treatments were tried for Botrytis, which often accompanies Sclerotinia, 

 but without any satisfactory result. 



Black Stalk Rot (Bacillus melano genes). — An organism has been 

 isolated and proved to be the cause of this disease. It was shown that 

 the organism is also capable of causing rot in turnips, swedes, carrots, 

 and parsnips, but not in mangolds. Experimental proof of the infection 

 of plants directly from the soil has not been obtained, and this is 

 considered as showing that the soil of Ireland is not as yet much 

 contaminated. The spread of the disease was shown to be mainly 

 due to the unsuspected planting of infected seed potatoes. The danger 

 of using apparently healthy tubers from a previously diseased crop 

 as seed was demonstrated in a remarkable manner, no less than 

 94 per cent, of the plants derived from the seed succumbing to Black 

 Stalk Rot. Great care should be taken in excluding all infected tubers 

 from the pits, as it was proved that the bacillus can pass through the 

 skin of a healthy tuber, in the absence of wounds, through the breathing 

 pores. Cool, dry conditions prevent the rot from spreading to any 

 degree, and such conditions should be established in making the pits. 

 Affected plants should be removed from the crop and burnt. 



Corky Scab (Spongospora subterranea Johns.). — Ten varieties of 

 potatoes have been tested, but none have been found immune to the 

 disease. Spore-balls of the organism would seem to pass unharmed 

 through the digestive tract of a pig, and the manure of the animal may 

 be a source of infection to a potato crop treated with it. The canker 

 form of the disease was proved to be more infectious than the spot 

 form. It was found that clean seed may become contaminated before 

 planting by contact with diseased seed. Liming was definitely shown, 

 both in 1909 and 1910, to increase the proportion of diseased tubers in 

 the crop. Several methods of treatment of affected seed tubers resulted 

 in a most satisfactory checking of the disease. These were soaking 

 in formalin solution (1 :6oo) for three hours, soaking in copper sulphate 

 solution (1 per cent.) for three hours, soaking in copper sulphate solution, 

 as before, followed by rolling in slaked lime, soaking in and covering 

 with precipitate of Burgundy mixture for three hours, and wetting 

 the surface and rolling in flowers of sulphur. Where copper salts 

 were used, however, the total yield of tubers was quite considerably 

 reduced. The best yield was given with the formalin treatment, and 

 the next best with sulphur. 



None of the methods tried for disinfecting the soil were satisfactory. 

 Lime, chloride of lime, and gas lime were found to increase the amount 

 of disease. Treatment with copper sulphate brought about some 

 reduction of the scab, but also decreased the yield. 



