1921.] Rot hams ted Experimental Station. 



785 



mately bound up with the time of application. Many farmers 

 are too late in their application of top dressings to cereal crops, 

 delaying until the plant has passed the stage when it can make 

 full use of the material supplied; it then develops a dark green 

 growth liable to rust, and a straw that tends to lodge. The 

 figures obtained at llothamsted are : — 



Increase in wheat crop, 1920, from spring dressings of sulphate 

 of ammonia and superphosphate. 





Grain — bushels per acre. 



Straw — cwt. per acre. 



Date of application 

 of maim e. 



Feb. 10. 



March 6. 



May 10. 



Feb. 10. 



March 6. 



May 10. 



Single dressing 

 Double dressing 



Nil 

 7 



0-9 



2 7 



3 7 



27 

 11-7 



6-9 



94 

 12 7 



The single dressing gave no appreciable increase in grain 

 and only a few cwt. of additional straw, while the double 

 dressing gave no less than 7 bush, of grain and 12 cwt. of 

 straw when applied at a safe and suitable time. In view of the 

 great practical importance of this work arrangements have 

 been made for continuing it on a larger scale. 



Diseases of Plants. — No reliable estimate can be made of the 

 losses of farm crops due to disease, but they must be con- 

 siderable. It is improbable that farmers could adopt the 

 individual treatment accorded to plants by gardeners; other 

 methods must be sought. Some diseases are due to insects, 

 some to fungi or various other causes. Separate laboratories 

 are being set up at Eothamsted for the study of insects and 

 fungi, but no detailed account of the work can be given as it 

 is still in its early stages and has not yet developed sufficiently 

 to justify application on the farm. In the entomological 

 laboratory Dr. Imms is trying to ascertain what substances 

 will attract insects. Beer and cane molasses proved very 

 effective as baits for traps; ordinary alcohol was of little use. 

 When, however, alcohol was mixed 'with a small quantity of 

 acetic, butyric or valerianic acid it became highly attractive. 

 Other work in this laboratory relates to the common bean 

 aphis. This insect goes through a remarkable life history, 

 and it spends part of its time on plants such as shepherd's 

 purse, docks, &c, which occur on most farms in sufficient 

 quantity for the purpose. Different varieties of beans vary in 

 their susceptibility to attack, and the possibility of finding or 



B 



