363 



FRIT FLY {OSCINIS FRIT) IN WINTER WHEAT. 



By F. R. PETHERBRIDGE. 



(School of Agriculture, Cambridge.) 



In a previous article 1 the writer has given examples of bad attacks of this 

 fly on winter wheat following leys containing either rye grass or Italian 

 rye grass. 



The following experiments show that this is due to the fact that 

 the autumn brood of flies lay their eggs on the grass, and that the larvae 

 feed on the shoots, and after the grass is ploughed in, they eventually 

 migrate to the young wheat plants. 



In 1917 a bad attack of frit fly was noticed on one part of a field of 

 wheat on the University Farm, whereas the other part of the field was 

 practically free from attack. 



The following shows the differences in the previous treatment of 

 these two pieces of wheat. 



Part A. Badly attacked by Frit Fly. 



Crop in 1916 — Italian rye grass and red clover. 

 Ploughed November 3rd, 1916. 

 Little Joss sown November 10th, 1916. 

 Part B. No Frit Fly attack. 

 . Crop in 1916 — Red Clover. 



Ploughed October 10th, 1916. 

 Little Joss sown October 23rd, 1916. 

 As a result of this and other observations, an experiment was ar- 

 ranged to see if the ploughing in of the rye grass before autumn would 

 prevent an attack of frit fly. 



In 1917 a piece of trefoil and Italian rye grass was divided into three 

 plots. 



Plot A was ploughed on July 1 2th, 

 cross ploughed on July 14th. 

 Cultivated from August 26th onwards. 

 Harrowed on September 26th. 

 Drilled on October 3rd. 



1 Loc. cit. vol. iv, Nos. 1 and 2, September 1917, 



24—2 



