J. ]:. c^^LLIx 111 



COXDl'I'IOXS FA\0L'1{AIU>K TO AX ATTACK. 



It is the universal opinion that hife sown spring crops are most 

 affected, and the evidence of many cases submitted to the Board of 

 Agriculture strongly supports this opinion. The date of the commence- 

 ment of the dangerous period is probably dependent upon weathci' 

 conditions and would therefore be best indicated by association with 

 some natural phenomeiui also governed by the same conditions. Past 

 experience has tended to show that spring corn sown before the end 

 of March is usually not attacked : occasionally it may be safe to sow up 

 to the middle of April on a gc^od tilth, but after that date an attack- 

 is very probable in /r?7-infested districts. Professor M'Cracken of the 

 Royal Agricultural College, Cirencester, writing to Miss Ormerod in 

 1889 (Ormerod. Report for 1889), stated that "Black Tartarian Oats 

 sown on March 29th enjoyed almost complete immunity from attack; 

 in another field sown on April 29th, over 70 % of the first stems were 

 destroyed" ; while in the Annual Report of the I nteUigence Division, Part 

 II, published by the Board of Agriculture in 1911, it was stated that 

 crops sown early in March have been known to escape when others 

 sown late in March were infested. In a Report on the breaking up of 

 Grass Land in England and Wales in the Harvest Year 1916-17, pub- 

 lished by the Board of Agriculture and Fisheries as Miscellaneous 

 Publications, N^o. 19, in 1917, it is stated that "Frit flies are most 

 troublesome in the case of crops sown in mid-season. Oats sown before 

 March loth and after April loth may escape when crops sown between 

 these dates may be destroyed." No authority for the statement that 

 oats sown after April loth may escape can be traced, while this statement 

 is certainly in opposition to the expressed views of all economic entomo- 

 logists in this country. Reports of bad frit-fly attacks on crops "after 

 grass" were frequently received in 1917, and it is worthy of note that in 

 Canada grasslands ploughed late in autumn or in spring are stated to 

 be attacked the worst (Criddle, 1916). 



. Enquiries instituted by the Board of Agriculture in 1909-10 aiid 

 published in Part II of the Annual Report of the Intelligence Division in 

 1911 appeared to show that late sown oats following roots fed by sheep, 

 when the fields v^"ere only once ploughed and not much cultivated, were 

 most attacked. Ormerod (Report for 1881) noted attacks on wheat on 

 land fallowed the previous year, no attacks where land ploughed first 

 time in autumn. Fitch (1881) stated that wheat after a whole summer's 

 fallow was almost invariably attacked. It must be remembered that in 

 some of these cases of attacks on wheat the real cause of the damage mav 



