78 AGRICULTURAL RESEARCH AND THE FARMER : 



progress to determine the period of the year during which the 

 danger of infection is greatest, the nature of the wounds most 

 susceptible to invasion b^-' the fungus, and the best substances 

 for protecting exposed wounded surfaces. 



University of Leeds. 



Dry Spraying for the Destruction of Charlock — Experiments 

 with dry sprays of some powdered chemical substances were 

 carried out during 1919 and 1920 by the Advisory Botanist 

 and his staff, with a view to ascertaining whether an efficient 

 and cheap dry spray could be recommended for districts where 

 the question of water supply presents a difficulty. The sub- 

 stances selected for the test were nitrolim, sulphate of iron, and 

 sulphate of copper (bluest one). The spraying was done in the 

 summer of both years, vvhen charlock was in full flower in 

 the fields selected for the experiment. The results indicate 

 that provided an efficient machine is used for the purpose, the 

 destruction of charlock by dry spraying is cheap and effective, 

 and should recommend itself to many farmers, particularly to 

 those who live in the more waterless districts of the country, 

 where the wet method has alwa3's been heavily handicapped. 

 It is important, however, that a suitable day should be chosen 

 for the operation. The weather should be fairly settled, and 

 there should be a heavy dew and no wind at the time of 

 apphcation. 



Common Scab in Potatoes. — Experiments have been conducted 

 to test the effect of liming the soil in relation to this disease. 

 Previous work at Leeds had been successful in definitely proving 

 the fungus origin of the disease, and in isolating the organism 

 responsible. These organisms are probably present in large 

 nimibers in the soil, v/here they play a beneficial role in the 

 initial stages of the decomposition of organic matter, and appear 

 to show a special preference for herbaceous plant residues, such 

 as leaves. The organisms apparently attack the potato tubers 

 only when the supply of their natural food in the soil becomes 

 exhausted ; thus common scab may be prevented by introducing 

 into the soil a sufficient quantity of green-plant matter, such as 

 grass or green manure, which presumably acts as a preferential 

 food for the scab-producing organisms, thus protecting the 

 potatoes from attack. Liming experiments carried out during 

 the last six years on a field scale showed definitely that Hming 

 the soil induces Scab, but that the effect can be neutralised by 



