258 



HORTICULTURE FOR SCHOOLS 



be exercised also to prevent moisture from standing on the 

 seedlings any longer than necessary. It is generally desirable 

 to water greenhouses and hotbeds in the morning rather than 

 at night, for the sunlight will dry off the plants and drive the 

 moisture from the stem. If moisture is allowed to remain on 

 the plants over night, they are much more susceptible to the 

 damping-off disease. 



370. Control of diseases. The control of plant diseases 

 is intimately connected with the whole subject of care in all 

 its aspects. The cultivation of the ground, the application 

 of irrigation water, the methods of pruning, and the disposal 

 of prunings and other rubbish, all have a direct influence on 



disease control. The 

 orchardist or gardener 

 must not only know a 

 great deal about bacteria 

 and fungi and the sprays 

 with which tr\ey may be 

 combated, but also must 

 pay attention to every 

 detail which enters into 

 the business of good 

 management. Only by so 

 doing can he hope to 

 wage a successful warfare 

 against plant diseases. 



The first step in control 

 of disease is the ascertain- 

 ing of the cause. This is 

 well illustrated in the case 

 of peach-rosette and peach-yellows (Figs. 132 and 133), two 

 diseases the causes of which are still unknown. Their 

 control is very difficult on that account. 



FIG. 133. Peach-rosette. 



