CERTAIN ELEMENTS IN NURSERY PRACTICE 197 



Control. Spraying with lime-sulfur solution 1 to 40, or 

 dusting with 90 parts dry sulfur plus 10 parts powdered ar senate 

 of lead, proves effective in the control of apple- and pear-scab. 



For nursery stock, the first treatment should be made soon 

 after the first new leaves appear. This application should be 

 followed by at least three more treatments at intervals of two 

 to three weeks. 



As a general recommendation for nurseries, it is not con- 

 sidered necessary to treat varieties of pear trees for scab except 

 the Flemish. In most nurseries it is not necessary to treat 

 apples each year for scab, but in some cases the treatment 

 proves profitable. Where the disease is commonly observed 

 on certain varieties of apples, such as Mclntosh and Transcend- 

 ent crab, spraying or dusting is advisable. 



APPLE POWDERY-MILDEW. This disease is most commonly 

 observed in the nursery on the foliage and young shoots of the 

 apple seedling stock. When it appears early in the summer, 

 the growth of the seedlings is checked and the bark does not 

 peel readily at budding time. 



Description. The disease appears as grayish white, felt- 

 like areas on the foliage, varying in size from a minute speck 

 to an inch in diameter. The diseased leaves are stunted and 

 have a tendency to crinkle and curl up. Affected shoots are 

 stunted and appear much shorter than healthy twigs. 



Cause. The disease is caused by a fungus, Podosphcera 

 leucotricha. The grayish patches of mildew on the leaf or the 

 shoot consist of a tangle of fine threads or strands of the 

 fungus. This loosely interwoven mass of threads (known as 

 mycelium) produces spores that are carried by wind and rain 

 to other leaves where they produce new patches of mildew. 

 The fungus lives over winter between the dormant bud-scales 

 or by means of special fruiting bodies. 



Control. Lime-sulfur solution 1 to 40 is effective to a 



