OVER-WINTERING OF APPLE SCAB. 191 



FURTHER OBSERVATIONS RELATIVE TO THE 

 ABILITY OF THE APPLE SCAB FUNGUS TO LIVE 

 OVER WINTER ON YOUNG TWIGS. 



W. J. Morse. 



Mention has already been made on p. 171 to observations made 

 at this Station which indicated that the scab fungus Venturia 

 pomi (Fr.) Wint. was able to remain alive over winter in 

 infected young apple twigs and that viable conidia found in the 

 pustules produced by the fungus on these twigs are at times a 

 source of spring infection on the leaves. 



In the spring of 1913 when these observations were made a 

 large number of specimens were received from various parts of 

 the State. In a number of instances where the conidia of the 

 fungus were still present, germination tests made in prune 

 decoction and prune agar indicated that they were still living. 

 Practically all of these tests were with material obtained from 

 diseased limbs collected in March and April. Pure cultures 

 made from the spores thus obtained, agreed in every respect 

 with those of V. pomi. Inoculations of young apple trees grow- 

 ing in the greenhouse with spores produced in these cultures 

 resulted in the production of typical cases of apple scab on 

 the leaves. 



While references to the over-wintering of apple scab on the 

 twigs are by no means lacking in European literature the writer 

 was unable to find, any previous record of similar observations 

 in America. In fact the general consensus of opinion among 

 pathologists in this country as expressed by their writings 

 appeared to be quite the contrary. Therefore, it seemed worth 

 while to continue these observations as opportunity offered. 

 While no such an abundance of material has been obtained since 

 the spring of 191 3 additional data has been secured each year. 



In 1914 one specimen was received in January and two in 

 February. In each case a few spores were found but not in 

 sufficient abundance to make germination tests. Specimens 

 received from one of the coast towns in the eastern part of the 

 State on April 15 carried sufficient spores so that positive germi- 

 nation tests were made in prune decoction. 



