368 Wormald . — 4 Brown Rot ’ Diseases of Fruit Trees. 
are cultivated on a much greater scale than the acid cherries, and on these 
M. fructigena is frequently found on the ripening fruit, while M. cinerea not 
only occurs on the fruit, but may sometimes cause a serious Blossom Wilt, 
as in the spring of 1918. 
Both species are found on ripening and mature plums ; sometimes 
M. cinerea is the predominant species present, on other occasions M. fruc- 
tigena. In 1916 two growers, one in Sussex, the other in the Maidstone 
district of Kent, complained of serious losses by Brown Rot at the time of 
picking ; samples sent to Wye College were found in each case to be 
affected by M. fnictigena only. On the other hand, an orchard of Czar 
and Bush plums, near Maidstone, visited by the writer at the time the fruit 
was being gathered in 1917, was found to be infected by M. cinerea almost 
exclusively, a few examples only being found with M. fructigena. In 
another orchard, plums (varieties Monarch and Victoria) were attacked by 
the two species almost equally ; in some instances the same cluster of plums 
bore both species, and occasionally the two were found on one and the same . 
plum (see Figs. 1 and 2). 
Both species occur on damsons, M. cinerea , as far as my own experience 
goes, being the more frequent. On peaches I have found M . fructigena on 
the ripening fruit and M. cinerea on dead twigs, but have not yet met with 
apricots affected with Brown Rot. 1 
{b) The ‘ Wither Tip ’ Disease of Plum Trees in 1918. 
This disease, which was prevalent in Kent in 1916, was practically 
absent in the following year, but reappeared with its former intensity in 
1918, when it was again (as in 1916) associated with an attack of aphides 
( Aphis pruni). Specimens of the ‘Wither Tip’ disease, received from 
Worcestershire and Norfolk, also bore traces of aphides on the leaves. 
The simultaneous occurrence on plum trees of the attack by the aphis and 
the outbreak of the Monilia disease of the vegetative shoots lends support 
to the theory that the insect renders the trees more susceptible to ‘ Wither 
Tip ’, either by aiding the dispersal of the conidia, by carrying them from one 
shoot to another, or by so injuring and weakening the leaves by punctures 
that the fungus is able to invade the tissues of the leaves and then the 
shoots ; probably both these factors are operative during a severe infection. 
Observations in 1916-17 proved that on diseased shoots infected in 
1916 pustules of Monilia cinerea appeared during the following winter and 
spring. An examination of the same twigs (which had been labelled on 
the trees) in 1918 showed that pustules with viable conidia were again to 
be found on some of them, though many bore no fertile pustules at that 
time. Such twigs, therefore, may serve as sources of infection for two years. 
1 While this paper was in the press apricot twigs, bearing a fungus morphologically identical 
with M. cinerea , have been received at Wye from Norfolk. 
