CONTRIBUTIONS FROM THE WISLEY LABORATORY. 



115 



OONTEIBUTIONS FEOM THE WISLEY LABORATOEY. 

 X. — Leaf-spot of Celery. 

 By F. J. Chittenden, F.L.S. 



During the years 1909 and 1910, and especially in the latter year, 

 celery was attacked to a remarkable extent in many parts of England by 

 a destructive parasitic fungus. Large numbers of diseased plants with 

 minutely black- spotted, dying foliage were sent to the Laboratory for 

 examination, mostly too late for much to be done to save the crop, and 

 in every case they were found to be attacked by the fungus Seiptoria 

 petroselini var. apii Briosi et Cavara. 



Severity of the Attack. — Many of the letters received spoke of the 

 severe nature of the attack. Thus, Mr. W. W. Eichmond Powell, of 

 Old Dover House, Canterbury, writing on September 30, says: " The 

 disease was first noticed about three weeks ago, and has since spread in 

 the rows with great rapidity. This disease, hitherto unknown to me, 

 is this year very prevalent in this locality. Last year plants close by 

 throve luxuriantly and without a trace of disease. Now, once the leaves 

 are attacked the plants begin to dwindle and some look like dying out. 

 Again, Mr. Herbert A. Powell, of Piccard's Eough, Guildford, writes: 

 " This is the second year that the disease has half-ruined the crop; " 

 and Mr. J. Muddell, of Sedgwick Park Gardens, Horsham: " I have 

 tried sulphur and fresh lime, but it does not seem to check the disease 

 in the least. I have eight hundred planted out, and I am afraid I may 

 lose the lot. It has attacked the late-planted plants within the last few 

 days." These extracts from correspondence, which are but examples 

 of many similar ones, will serve to emphasize the severity of the attack 

 and the necessity for watchful care and prompt attention if the disease 

 should appear this season. 



Symptoms of the Disease. — Usually the earliest symptom of the 

 attack is the appearance of small pale spots, light brown, or yellowish, 

 upon the otherwise healthy-looking leaves ; on these spots close exami- 

 nation reveals the presence of numerous somewhat sunken, small black 

 dots, scarcely visible to the naked eye, but easily seen by the aid of a 

 lens. The pale spots upon the foliage, which are totally unlike the 

 burrows made by the celery-fly larva, render the presence of the disease 

 quite evident, but when the attack is really severe these spots are prac- 

 tically absent, and the whole leaf becomes an almost olive green owing 

 to the enormous number of black points scattered over its surface 

 and visible on both sides of the leaf. This appearance is quickly fol- 

 lowed by the wilting of the fohage and the decay of the leaf stalk, which 

 often shows the little black points upon it a*s well. In America, where 

 celery is frequently lifted in the autumn and stored in sheds, the disease 



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