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Potato Spraying Trials. 



[JUNE, 



POTATO SPRAYING TRIALS IN THE 

 CAMBRIDGESHIRE FENS, 1919. 



F. R. Petherbridge, M.A., 



School of Agriculture, Cambridge. 



The experiments dealt with in this article are a continuation 

 of those started in 1918, an account of which appeared in this 

 Journal for January, 1919. 



They were caried out on two fields lent by Mr. F. Hi am 

 (Putney Hill Farm, Prickwillow), who bore the cost of the 

 labour connected with the experiments. 



The work for the year was planned to form part of the trials 

 on the effect of spraying over a series of years, and also to find 

 out if machines applying over 200 gal. per acre are likely to be 

 more profitable than those at present on the market which apply 

 about 100 gal. per acre. 



The season of 1919 was an exceptional one from the point 

 of view of potato blight. There can seldom have been a season 

 in which bhght did less damag:e. The fact that Up-to-Dates, 

 planted in April on a gravel soil near Cambridge, were dug in 

 October free from blight will serve to show that this disease 

 had practically no effect on the yield of late varieties in this 

 district. 



Blight was first found at Prickwillow in a field of Eclipse 

 on July 28th, and here it spread slowly until the lifting was 

 finished on August loth. On the experimental plots " blight " 

 was found both on the Majestic and Evergoods on August ist, 

 but throughout the season it spread slowly, so that it was not 

 possible until the middle of September to find more than a 

 slight trace of it on the haulm. Growers would have regarded 

 these plots as free from blight until the middle of September. 



The Spraymgr — The mixtures used were as follows : — 



(i) One per cent. Bordeaux Mixture. — This was made in a 40-gal. 

 tub. In the tub 4 lb. of copper sulphate were dissolved in about 

 50 gal. of water. As Buxton lime was not obtainable, ordinary 

 builder's quick-lime was used : 2 to 2 J lb. of Buxton lime is usually 

 sufficient for 4 lb. of copper sulphate, but more than this quantity 

 of the builder's lime was used. It was slaked in a large bucket, 

 and then made into a milky solution by the addition of water, 

 and after settling w^as poured through a sieve covered with coarse 

 sacking into the copper sulphate solution. The mixture was then 

 well stirred and lime water added until no brown colour resulted 

 with the potassium ferrocyanide test. Water was then added to 

 make up the 40 gal. 



