192 THE NURSERY-MANUAL 



chine. With the dust method, the time of application is not 

 limited by soil conditions, inasmuch as the lightness of the 

 outfit permits its transportation at all times; also blocks of 

 trees on rough or hilly ground or in localities remote from an 

 adequate water supply may be protected without unusual 

 difficulty. The dusting method can be employed in controlling 

 a large percentage of the leaf diseases and foliage-eating insects 

 in the nursery. The cost of spraying solutions is less than 

 dust materials. The actual expense for the dust method, 

 however, is practically the same as for the liquid since the 

 handling of a large bulk of water is eliminated, the outfit is 

 less expensive, and the operators are fewer in number. 



Diseases caused by fungi and bacteria 



The nursery-stock diseases caused by fungi and bacteria 

 are particularly baffling because the organisms are not seen 

 and recognized. In former days these disorders were ascribed 

 to the weather, to electric currents and to other little under- 

 stood or occult phenomena. 



FIRE-BLIGHT. The fire-blight disease is most destructive 

 on the cultivated varieties of pear, apple and quince. Usually 

 in the nursery it means total loss of the trees affected and often 

 within a comparatively short time thousands of young trees 

 are ruined by its rapid spread through the blocks. 



Description. The limbs, blossoms, twigs and fruit may be 

 attacked. In the nursery the disease is most commonly found 

 in the twigs (Fig. 210). In the case of two- and three-year-old 

 quince stock, however, the trees often blossom profusely in 

 the spring and when this happens blossom-blight (due to the 

 same organism) frequently occurs. The blight usually first 

 appears two or three weeks after the blossoming period. The 

 first evidence of the trouble is the brown and subsequent 



