DISEASES 



DISEASES 



493 



Colony of apple-scab. 

 Natural size. 



cherry tree. The limbs affected are practically worth- 

 ies^ ;unl l>y destroying them the disease is kept from 

 preading further in the branch and the forming spores 

 art- destroyed before they have an opportunity of get- 

 ting a foothold elsewhere. 



It' the horticulturistunderstands the methods of growth 

 and propagation of a destructive fungus, he is better 

 able to take the step that may lead to the eradication of 

 the pest. Let another example 

 be taken, namely, the apple- 

 leaf rust, which in some parts 

 of the country is a serious 

 menace to the orchardist. It 

 is recognized as yellow 

 blotches upon the foliage, fol- 

 lowed by groups of deep cups 

 in the under half of the leaf 

 tissue, where orange-colored 

 spores are produced in great 

 abundance. The life cycle of 

 this fungus, Gymnosporan- 

 ijinnt macropus, involves two 

 hosts; that is, it lives in one 

 stage upon the common red 

 iedar and in the next it infests 

 the apple tree. Upon the cedar the fungus, forms galls 

 of a chocolate color half an inch or more in diameter, 

 which during the spring rains become swollen and have 

 a gelatinous exterior. In this jelly the spores are pro- 

 duced that find their way to the apple tree and there 

 form, after vegetating for a few days, the destructive 

 rust. It is seen that in a case like this the most impor- 

 tant thing is to destroy the cedar-galls, for in them the 

 fungus passes the winter; and this can be done 

 by picking and burning. To those who do not 

 set a high value upon their cedar trees, the end 

 may be accomplished by removing the cedar 

 trees that stand at all near the infested 

 orchard. 



But there are many destructive fungi 

 that pass their whole life upon the 

 same plant, and the method men- 

 tioned for the apple rust would not 

 obtain. In many such cases the 

 use of fungicides has proved ef- 

 fective. The apple-scab (Fig. 721), 

 due to a fungus (Fusicla- 

 dinm dendriticum),is a good 

 case in point. It infests both 

 the leaf and the fruit, caus- 

 irregular blotches upon 



722. Peaches of last year's crop still hanging on the tree, 



attacked by monilia (X %). 

 The branch is dead from the effects of the fungus. 



both, and frequently destroying the crop. Many ex- 

 periments have demonstrated that this scab-produc- 

 ing fungus can be kept down by the nse of the Bordeaux 

 mixture and various other similar substances. The fun- 



gus thrives below the skin of the fruit and the epider- 

 mis of the leaf, producing: spores in abundance upon the 

 surface. The fungicide, when left in a thin film upon the 

 susceptible surface, prevents the germination of the 

 spores and the extrance of the fungus. It likewise may 

 kill the spores in the places where they are formed and 

 before they have been transplanted to another part of 

 the plant. The fungicide cannot act as a cure in the 

 sense of replacing the diseased, by healthy tissue, but 

 may, by destroying the spores, so prevent the spread that 

 the healthy parts may predominate. In the case of foli- 

 age, the spraying is "chiefly preventive, and should be 

 particularly directed to the younger leaves, the older 

 ones, with the fungus already established in them, in 

 time falling away. With the ordinary fruits there is no 



723. Effects of the leaf-curl fungus on peach foliage (X %). 



such succession, and the aim is to have each apple or 

 pear coated with the fungicide. 



As a rule a fungus that attacks the fruit also infests the 

 leaves, and may likewise thrive in the stems. From this 

 it is gathered that the spray should be very thoroughly 

 applied to all parts of the plant, in order that the foliage 

 may be kept in vigor and make the required food sub- 

 stances for the growth of the fruit, and the latter saved 

 from decay due to direct attack of the fungous germs. 

 But this is not enough. From what has been remarked 

 concerning the hibernation of fungi, it goes without long 

 argument that much can be done by thorough sanitation 

 in the orchard and fruit garden when the crop is off and 

 the plants are at rest. In short, the foliage of a blighted 

 orchard or vineyard is too important to be overlooked 

 in considering the subject of fungous diseases. The pear 

 leaves, for example, may be infested with the leaf-spot, 

 Entomosporium maculatum, and spraying may have kept 

 them from falling prematurely and a good crop saved 

 thereby, but the old leaves, as they drop in autumn, are 

 more or less infested with the disease, and, as far as pos- 

 sible, should be destroyed before the winds have scat, 

 tered them. In the same way the black-rot of the grape 

 (L&stadia BidwcUii} maybe carried over in the foli- 

 age and the mummy berries that are left upon the vines. 

 Here, again, the spray pumps can.be largely supple- 

 mented by picking, pruning and burning. In the winter 

 care of vineyards we can take a lesson from the grape 

 growers of Europe, where much care is taken to clean 

 up after every crop. They do not stop with the gather- 

 ing of the refuse, but spray the leafless vines in win- 

 ter, and the trel ises as well, with Bordeaux or plain 

 solution of cupric sulfate. The subject of remedies for 

 fungous diseases would be slighted were not emphatic 

 words used in this connection. It is folly to delay the 



