APRIL 



IRISH GARDENING, 



57 



A Serious Disease of Beans. 



By G. H. Pethybridc.e, Ph.D., B.Sc. 



IN p.assing- a fruiterer's shop in Dublin last autumn 

 my attention was attracted by some beans which 

 were exposed for sale, but which were rather 

 curiously marked with more or less circular black spots. 

 On obtaining some of them and examining them more 

 closely it was found that 

 these spots were somewhat 

 depressed, blackened areas 

 of the bean pod, shallow 

 circular pits in fact, with 

 rather lighter coloured 

 margins. In the bottoms of 

 these pits small pustules 

 were to be seen of a rather 

 dirty white colour, and the 

 general appearance of the 

 pods is well illustrated in 

 the accompanying photo- 

 graph of two of them. 



It was easy to diagnose 

 the trouble as the Bean 

 Anthracnose, caused by a 

 parasitic fungus rejoicing 

 in the long name of CoUcln- 

 t rich u m L in dem it th ia n n ni 

 Briosi at Cavara (:= Gloeo- 

 spo rium Lindem uth ian n tn 

 Sacc. et Magn.). The rava- 

 ges of this fungoid pest 

 have been the subject of 

 investigations for a con- 

 siderable number of years, 

 commencing with the 

 earliest studies of the fun- 

 gus made by F"rank in 

 Germany in 1883. Latterly 

 a good deal of attention 

 has been paid to it in the 

 United States of America, 

 particularly by Whetzel. of 

 the Cornell University 

 .Agricultural Experiment 

 Station. Bulletin No. 255, 

 issued by this Station in 



May, 1908, contains a well illustrated account of the 

 disease, and reference should be made to it by those 

 who desire fuller details on the matter. 



The object of this note is to call attention particularly 

 to two points in connection with this disease. The first 

 is its serious nature. In certain seasons, particularly 

 rainy ones, the attack may be so severe as to destroy 

 the whole bean crop, and recognising the seriousness 

 of the disease the authorities of the above named 

 Station have considered it necessary to detail a special 

 assistant to devote a large part of his time during a 

 period of three or more years to investigations upon it. 



The second point is that this disease is one of those 

 comparatively rare ones in which infection is carried 

 from one season to the next and from one locality to 



Photo by] 



Beans Showing A 



another by means of seed. The fungus forms its 

 characteristic canker-spots on any part of the bean 

 plant above ground, but of course is most destructive 

 when it attacks the pods, as it usually does to an extent 

 greater than that of any other part of the plant. From 

 the pods the infection spreads to the seeds within them, 

 for the fungus mycelium grows through the wall of the 

 pod and the skin of the young bean seed, and then 

 reaches the cotyledons of the embryo bean plant, where 

 it lies dormant during the period of rest of the seed. 

 Such infected seed may be 

 recognised, especially on 

 white beans, by the rusty 

 red spots of varying sizes 

 on the seeds ; on coloured 

 seeds, however, this is a 

 matter of much greater 

 difficulty. When infected 

 seed germinates the coty- 

 ledons of course come 

 above ground, and from 

 the fungus spots on them 

 spores are liberated in 

 abundance, which carry 

 infection to all parts of the 

 plant. It has been found 

 in practice that hand pick- 

 ing the seed and removing 

 the diseased ones is not a 

 sufficient means of eradi- 

 cating the disease, or even 

 of partially controlling it. 

 Pn-sumably by this method 

 seeds which are only 

 slightly diseased may 

 easily be overlooked, and 

 moreover there is alwaj'S 

 the possibility of the 

 spores of the disease being 

 carried over to the next 

 season by mechanically 

 adhering to the surface of 

 even healthy seed which 

 has been in contact with 

 diseased seed. Further, 

 experiments carried on 

 over three seasons to test 

 the efficacy of sprajing 

 the growing plants with 

 Bordeaux mixture have shown that this method 

 of control is not eff'ectual. Nor has treatment of 

 aff'ected seed with fungicides been of any avail, 

 for when attacked the seeds contain the fungus 

 wifhiti their tissues, and no mere external application 

 of a fungicide can be expected to reach the seat of 

 trouble without injury to the seed itself. The only 

 satisfactory method of obtaining clean seed seems to 

 be to select it exclusively from those pods which are 

 absolutely free from fungus spots. Gardeners should 

 carefully examine any seeds of French or kidney beans 

 which they propose to sow, and samples showing any 

 seeds with rusty or brownish spots on them should not 

 be used for fear of introducing this pest into Irish 

 gardens. 



[G. H. rethyhridg 

 NTHRACNOSE DlSKASE 



