192(2.] Anthracnosb of the Cucumber Under Glass. 4G9 



experimentation on the lines of the differential soil tests here 

 discussed should lead to the establishment of a simple and effecr 

 tive test. 



****** 



ANTHRACNOSE OF THE CUCUMBER 



UNDER GLASS. 



W. F. Bhwley, D.Sc, 

 Director, Experimental and Research Station, Chcshunt. Herts. 



Under the name " Spot " disease, the commercial cucumber- 

 grower groups all the »leaf diseases of that plant. The most 

 important leaf spot diseases of the cucumber are those caused 

 by the fungi Cercospora melonis and Collctotrichum oligochae- 

 ln m, while under conditions of abnormally high humidity Clado- 

 sporium c a earner inum may be a destructive parasite. 



During the years 1897 to 1907 Cercospora melonis appeared 

 in the Lea Valley and caused great destruction, but the introduc- 

 tion of the variety Butcher's Disease Besister in 1903. which 

 is immune to this fungus, and of methods of soil sterilisation 

 led to its ultimate disappearance. At the present time Cerco- 

 spora melonis exists only in isolated parts of Great Britain. 

 The Cercospora disease was soon followed by another caused by 

 CoUetotricham oligochaetum. This is the Anthracnose of 

 cucumbers which is now the most important leaf spot disease of 

 the cucumber in this country, and causes many thousands of 

 pounds' damage each year. 



Disease Symptoms. — C. oligochaetum has been observed to 

 cause a " damping off " of cucumber seedlings and young plants 

 on several occasions, but this form of the disease is not com- 

 mon. The fungus attacks the young plants at approximately the 

 ground level, and causes a shrinkage of the tissues, so that the 

 plant falls over. It spreads rapidly up the plant and gives rise 

 to spore masses in about five days. 



In its commonest form the disease first attacks the leaves and 

 may appear at any time during the life of the plant. It has occa- 

 sionally been observed during the propagating period, but gene- 

 rally it does not appear until March or April when the plants are 

 well established in the houses and some fruits have been cut. 

 The time at which the plants are attacked bears no relation to 

 their age, but is determined by the presence of suitable BOOrces 

 of infection. On the leaves, the spots generally first appear 

 above a vein, presumably because the spores are washed into 



