CERTAIN ELEMENTS IN NURSERY PRACTICE 209 



decay when subjected to the moist condition of the storage 

 cellar. 



Description. The leaves, the blossom buds and the young 

 shoots of roses are affected by mildew. The disease appears 

 as white irregular blotches, causing the leaves to become curled 

 and dry. The bark of severely affected shoots becomes dead 

 in appearance and shrivels, causing an arching or a curving 

 of the shoots at the tip. Only the current year's growth is 

 affected. 



Cause. The fungus Spharotheca pannosa is the cause of 

 the mildew on peach and rose stock. Spores of the fungus are 

 produced in the white blotches of mildew and these propagate 

 the parasite throughout the summer. After midsummer the 

 special fruiting bodies known as perithecia also may be pro- 

 duced and these serve to carry the fungus over winter. 



Control. Most copper sprays have not proved effective in 

 controlling this disease. A sulfur dust-mixture is more effective 

 than bordeaux mixture or lime-sulfur solution. Applications 

 of a dust mixture employed in the control of the black-spot of 

 roses will also prove effective in checking the mildew. 



Insect pests of nursery stock 



The insect depredations in the nursery are probably better 

 known as to kinds and causes than the diseases, yet some of 

 them are difficult of control. The treatment for diseases and 

 pests is often much the same, if not even identical, and there- 

 fore the two should be understood together. 



PLANT-LICE OR APHIDS. There are numerous species of 

 sucking insects, known as aphids, infesting various kinds of 

 nursery stock, as apple, quince, rose, cherry and certain orna- 

 mentals (Fig. 221). The plants are frequently seriously in- 

 jured, the leaves being badly curled and the growth checked. 



