'24 



BLOSSOM-WILT OF APPLES. 



(Monilia cinera, forma mail.) 



Blossom-Wilt is a comparatively new disease. It is a 

 trouble which affects not only the blossoms but the spurs and 

 the shoots. The disease was first described from Kent, where 

 it is very common, but it is now known to occur in many other 

 parts of the country and to be responsible for serious losses of 

 crop. In some orchards it has reached epidemic proportions 

 and in many cases the apple crop may be reduced to one 

 quarter or even less. Lord Derby is the variety most often 

 attacked, but Cox's Orange Pippin, James Grieve and many 

 others also suffer. 



The disease is caused by the fungus Monilia cinerea, a very 

 near ally of Monilia fructigena, the cause of Brown Eot of 

 apple fruit (see Leaflet No. 86). The two fungi may be distin- 

 guished by the colour of the spore-pustules, those of the 

 former being a pale grey and of the latter being buff. Other 

 and sharper distinctions are discernible by laboratory methods. 

 M. cinerea is best known on plums and other stone fruit, and 

 the form which attacks apple blossom is known as forma mali. 



The "Blossom-Wilt" Stage. The first evident symptom 

 of the disease, which, in its early stages, is easily overlooked, 

 is the " blossom-wilt " condition (see Fig. 1). About a fort- 

 night after the flowers begin to open, the leaves on some of 

 the spurs will be seen to be beginning to wilt; within a day 

 or two these drooping leaves become brown and withered, 

 usually with incurved margins. The flowers of such trusses 

 will be found to have wilted and to be brown and dead. In 

 susceptible varieties many trusses on a tree may be affected. 

 The destruction of the blossoms is, however, only a minor part 

 of the damage caused by the fungus, as, after killing the 

 flowers, it usually proceeds to grow through the flower stalk 

 into the spur. 



The life-history of the parasite has been worked out by 

 Dr. H. Wormald, of Wye College.* He showed that the 

 infection of the flower-truss takes place through spores 

 alighting on the stigmas of the blossoms. These spores are 

 derived from the spore-pustules which develop on the spurs 

 and wood which was attacked the previous season. It was 

 ascertained that the death of the flower follows very soon 

 after the infection of the stigma, and within a fortnight the 

 fungus has so far advanced as to a*ffect the young leaves and 

 cause them to droop as noted above. If the weather is dry 

 the fungus keeps within the tissues of the flowers and leaves 

 and does not show itself at all from without, but in moist 

 weather it develops externally on the flowers and flower-stalks 



* For a fuller description see article by H. Wormald in Jour. Board 

 Agric.., Vol. XXIV., Aug. 1917, pp. 504-513. 



