172 



IRISH GARDENING. 



" Brown Rot " of Apples. 



By H. WoRMALD, M.Sc. (Lond.), A.R.C.Sc, 

 Mycological Deijartment, South-Eastern Agri- 

 cultural College, Wye, Kent. 



The Disease or. the Tree. — During summer and 

 early autumn ajsple trees are frequently attacked 

 by a disease which produces on the fruit brown 

 areas which gradually increase in size until the 

 wliole apple is affected ; meanwhile, small pus- 

 tular swellings appear beneath the skin and soon 

 burst through as yellowish, powdery, cushion- 

 like outgrowths, usually in concentric circles. 

 The diseased apples begin to shrink in size and 

 the skin becomes wrinkled. Such fruits, when 

 hanging loosely, are easily detached and many 

 fall to the ground during a high wind ; the rot 

 continues to develop on these windfalls, and more 

 pustules are produced, to act as a possible source 

 of further infection. When, however, a diseased 

 apple is in contact with other apples or with a 

 branch the pustules produced at the point of 

 contact become adherent and may so attach the 

 apple to the tree that some 1 ttle force is required 

 to detach it. 



Method of Attack by the Parasite. — The disease 

 is caused by the fungus Monilia fructigena, Pers. 

 (= Sclerotinia fructigena, Schroeter). The 

 powdery pvxstules which sooner or later appear 

 on the affected apples are outgrowths of the 

 fungus growing in the flesh of the fruit, and each 

 consists of numerous chains of spores or rejiro- 

 ductive bodies. The spores readily fall apart 

 and are easily scattered by the wind or carried 

 by insects to other apples. When they gain access 

 to the flesh of an apple throvigh any cut or 

 rupture of the skin they germinate within a few 

 hours, producing fungal threads (mycelium) which 

 develojj within the tissues and cause the char- 

 acteristic "brown rot." 



The rapidity with which the rot travels through 

 the apples is illustrated by au experiment which 

 was carried out in the plantation at Wye College 

 in the summer of 1917. 



On the 24th of July, while the apples were 

 actively growing, and about 1 inch in diameter, 

 ten of them were artificially injured by making 

 a single puncture through the skin by means of 

 a sterilized needle, and inserting in each puncture 

 spores of Monilia fructigena, taken from a pure 

 culture of the fungus which had been grown in 

 the laboratory. Two days later it was seen that 

 a brown rot had already made some progress, 

 for ro\ind each puncture there was a discoloured 

 area varying from one-eiglith to half an inch in 

 dianieter. 



At the end of six days from the beginning of 

 the experiment about half the surface of each 

 of the ten inoculated apples was brown, while 

 the rest of the apples on the tree showed no 

 trace of the rot. A few pustules had by this 

 time appeared on each of the ten, in a zone at 

 about half an inch from the puncture ; they were 

 of a buff yellow colour, and when fully developed 

 were about one-tenth of an inch in diameter. 



Nine days later the whole surface of each in- 

 oculated apple was brown and bore numerous 



powdery pustules. Strong winds whicli occurred 

 about this time caused nine of the apples to fall ; 

 the remaining one had been in contact with the 

 branch and the pustules on that side had so 

 attached themselves to tlie bark that although 

 the stalk of the apple had become almost de- 

 tached from the fruiting spur the fruit itself 

 remained fixed to the branch by means of the 

 pad of fungal threads. 



When an infected apple is in contact with 

 others on the tree the latter may become infected 

 by contagion, and frequently a bunch of apples 

 is found which shows fruit with the rot at various 

 stages of developnient. 



Mummied Ajiples and MetJiods of Over- 

 ivintering. — Those diseased apples which become 

 attached to the tree usually remain in that 

 position throughout the winter, becoming dry 

 and shrivelled, and they constitute the so-called 

 " mummied " apples. Many of the spores on the 

 pustides of these " mummies " are washed av/ay 

 by rain or dispersed by the wind in winter ; 

 others remain on the pustules, but these usually 

 lose their power of germination. As summer 

 approaches, however, the " mummies " produce 

 a new crop of spores and these cause infection 

 of the young fruit. A " mummy " frequently 

 infects the growing apples directly by contact, 

 but in any case api^les in the neighbourhood of a 

 " mummy " are liable to spore-infection through 

 wounds, and such newly-infected fruit will 

 soon produce myriads of spores which 

 serve to spread the disease. The spores 

 are minute in size (only about 12^00 inches in 

 length), and are easily dispersed by the wind ; 

 insects, too, crawling over the fruit may not 

 only carry the spores from one apple to another, 

 but biting insects, such as wasps, also produce 

 wounds enabling the spores to reach the exposed 

 flesh of the apple where they grow rapidly and 

 reproduce the rot. 



Spur Canker. — On sonie soft-wooded varieties 

 of apples [e.g.. Lord Derby and James Grieve) 

 it has been observed that the disease may extend 

 along the stalk of the affected fruit and into 

 the fruiting spur, or even as far as the branch 

 itself, producing in the latter a canker round 

 the base of the spur. In this capacity of forming 

 cankers it resembles the " Blossom Wilt and 

 Canker Disease " of apple trees caused by a 

 closely-related fungup (i.e., Monila cinerea, Bon.), 

 and already described in The Journal of the 

 Board of Agriculture. The two diseases are, 

 however, quite distinct. In the case of the 

 " Blossom Wilt," infection occurs through the 

 open flower, while in the disease described in the 

 present article infection takes place, so far as is 

 known only through the fruit. 



Control ]\rEASURES. — From the preceding 

 remarks it will be seen that the mummied fruits 

 which are allowed to remain on the trees through- 

 out the winter are the source of the new infection 

 of the growing and ripening apples, and that the 

 one certain preventive measure against the 

 disease is the renioval of the affected fruit from 

 the trees. In gardens, allotments and small 

 orchards it is possible to examine the trees at 

 frequent intervals, and any apple showing a 

 brown rot, even in an early stage of development, 

 should be promptly removed. On large fruit 

 farms such a course would in most cases be 



