18 



As is the case in the United States and Canada, a reduction 

 of crop occurs, specially with certain varieties, when lime- 

 sulphur is used, a certain number of fruits falling in June. 

 This matter is also being investigated at East Mailing. 



APPLE MILDEW. 



(Podosphaera leucotricha, Salm.) 



Apple Mildew is an extremely widespread disease and it 

 occurs in almost all countries wiiere the apple is cultivated. 

 The mildew has been repeatedly studied, especially in 

 Europe and America, and, with the exception of a few 

 special cases, it is now possible to keep it under control if 

 the proper measures be adopted. In England the disease is 

 of common occurrence and may cause a considerable amount 

 of damage, especially in the case of certain varieties. During 

 recent years it appears to have been increasing in severity, 

 and reports have been received from several apple growing 

 centres in which, owing to serious and persistent outbreaks, 

 extensive damage has been caused. Pears also are attacked 

 by the same mildew, but in this country not severely. 



Cause of the Disease. Apple mildew is caused by the 



fungus Podosphaera leucotricha. It is closely related to the 

 other true mildews, such as those of the Hop, Eose, and Goose- 

 berry, and especially to that so commonly found on Hawthorn 

 hedges, but is distinct from all, and is confined in its attacks 

 to the genus Pyrus. The fungus consists of the mycelium, 

 very slender threads (corresponding to the spawn of a 

 mushroom) which creep over the surface of the host plant, 

 and masses of conidia or minute spores, which appear as a 

 white mealy powder on the surface of the mildewed area, 

 and which, like seeds, serve to propagate the fungus. The 

 mycelium of the fungus obtains its nourishment by means 

 of minute suckers inserted into the tissues of the leaf. 



Description of Affected Plants. Affected leaves show the 

 curled and white appearance characteristic of most mildews. 

 The mealy substance or mass of spores is at times very 

 abundant and hence with favourable weather the disease 

 spreads rapidly. The mildew commences each year with the 

 unfolding of the buds in spring. Both flower bud? and leaf 

 buds may be affected (Fig. 1). In some cases the flowers are 

 so injured that the whole truss fails to set and the buds die, 

 and if many are thus attacked a considerable loss of crop may 

 result. Leaf buds which are affected . may in like manner 

 be killed outright, but in the majority of cases they survive 

 and continue to grow, each new leaf which develops being 

 generally more or less affected with the mildew as also is the 

 " wood " itself. The leaves or other part of jhe tree are 



