190 THE NURSERY-MANUAL 



long, twenty feet wide and ten feet high in the clear, will winter 

 about 25,000 three-year-old apple trees, if the trees are corded, 

 as already described. 



While ventilation should be provided, the house may never- 

 theless be kept close in cold weather. If the temperature runs 

 but little above freezing, there is little withering nor does mold 

 develop. Some houses are provided with refrigeration. Keep- 

 ing houses too warm and allowing .air to blow through are 

 likely to devitalize the stock. 



IMPORTANT DISEASES AND INSECTS AFFECTING NURSERY STOCK 



Prepared for this Manual by the late V. B. Stewart, Bureau of Plant 

 Industry, United States Department of Agriculture, and of Cornell Uni- 

 versity, specialist in nursery-stock diseases. Fumigation and inspection, 

 not dealing with the growing and perfecting of the stock, are not treated 

 here. Growers will do well to consult such works as E. F. Smith on 

 "Bacterial Diseases of Plants" (Sanders, Phila.), and the Rural Manuals by 

 Hesler & Whetzel, Rankin, Slingerland & Crosby. 



The important problem confronting nurserymen is the 

 production of the greatest quantity of first-class stock to the 

 acre within the shortest period of time. Such conditions as 

 weather, soil, cultivation, and presence of certain destructive 

 diseases, are some of the factors that influence the develop- 

 ment of nursery plantings. Of particular importance is the 

 effect of various plant diseases and insects. The stock may 

 have developed very rapidly and be perfectly healthy, when 

 within a very short time conditions may change and the plants 

 become seriously injured or totally ruined by a destructive 

 disease or insect. 



The losses in the nursery caused by diseases are often very 

 heavy. Some diseases, such as fire-blight, completely destroy 

 the stock attacked unless the disease is eradicated by cutting 

 out the affected parts. Other diseases affect only the foliage 

 and are a menace to nursery stock by causing the leaves to 



