1905.] 



The Cucumber Leaf Blotch. 



19 



THE CUCUMBER LEAF BLOTCH OR "SPOT" 



DISEASE. 



The Cucumber Leaf "Spot" disease {Cercospora melonis), 

 of which an account is given in the Board of Agriculture leaflet 

 No. 76, continues to work great havoc among the market growers 

 of cucumbers in the Lea Valley. Various methods of meeting 

 the attack have been tried, but so far without any effect. 

 In one range of houses near Harpenden, spraying with Bordeaux 

 mixture and with a solution of liver of sulphur failed to check 

 the disease, so that last winter a very thorough campaign was 

 •entered on to get rid of it. First of all, the empty houses were 

 washed down with a 5 per cent, solution of copper sulphate ; 

 everything was well wetted with this, and the surface soil satu- 

 rated so as to get rid as far as possible of spores within the house. 

 Fresh soil was introduced for the new crop, and the young plants 

 were raised in a house that had been free from disease. To give 

 the plants every chance, a good dressing of potassium sulphate 

 was incorporated with the new soil. On March 25th the treat- 

 ment recommended by Mr. G. Massee {Jour. Roy. Hort. Soc, 

 Vol. XXVIII., 1903, p. 142) was begun, and the soil was watered 

 -every fourth day with a solution of copper sulphate containing 

 1 oz. copper sulphate in 36 gallons of water. This treatment 

 seemed at first successful, and one cutting of cucumbers was 

 obtained ; but just as the plants should have been in their 

 most vigorous bearing, they collapsed as badly as ever with 

 the "spot" disease, and had to be cleared out. The spots had 

 never been absent during the copper treatment, but at first they 

 -did not appear to run so readily as they had done in former years, 

 until, with some change in the weather or other unknown cause 

 the attack became as virulent as ever. It was also noticed that 

 the treatment seemed to render the plants more susceptible 

 than usual to red spider, which was rampant at the time 

 the plants collapsed. 



On the whole, it appeared as though the copper treatment 

 deferred the attack somewhat ; but as soon as the strain of 

 bearing fell upon the plant it had not vigour to maintain itself 

 .against the joint attack of the fungus and the red spider. 



