ILLINOIS TREES: SELECTION. PLANTING, AND CARE 29 



amounts in the soil. In the forest, where humus accumulates year 

 after year, trees are liberally supplied with organic material 

 derived from decaying leaves and plants. This material supplies 

 nutrients and helps to retain soil water. Since natural sources 

 of nutrients and water often are insufficient along city streets, 

 in lawns, or in parks, fertilizing and watering are frequently 

 necessary. Well-nourished trees appear to be more resistant to 

 drought than those that lack proper nourishment. 



Recommendations on fertilizing trees, based on current re- 

 search, are available from the Natural History Survey on request. 



Watering 



Although shade trees generally do w^ell in Illinois without 

 watering, lack of water during prolonged dry periods or as a 

 result of temporary or permanent lowering of the soil water 

 table can cause serious injury or result in death of trees. You 

 can supply water to the surface of the soil or through a grid of 

 holes that reach to the root level. Lances or needles (Fig. 27) 

 offer a convenient means for soaking the soil around tree roots. 

 In surface watering, you can use sprinklers or soakers, or allow 

 the water to run slowly from a hose. Soak the soil to a depth of 

 approximately 14 inches. Generous waterings at 2-week intervals 

 give better results than frequent light waterings. 



Spraying 



Sprays are used to control insects and diseases, to kill brush 

 and other undesirable plants, and to correct nutritional de- 

 ficiencies. The effectiveness of any spray material depends on ob- 

 taining complete coverage of the treated parts with the proper 

 material at the right time. 



You can control most insects by applying insecticides after 

 the pests have appeared. To control diseases, however, fungi- 

 cides should be applied as protectants before infections occur, 

 and not as cures after the diseases have appeared. Since fungi- 

 cides are applied to the surface of plants, they act as barriers 

 i or protectants against germs. Therefore, they are of major im- 

 ; portance in the control of foliage diseases. Many pests do not 

 cause serious damage each year and it is not necessary to spray 

 I annually for their control. However, trees subject to repeated 

 attacks of a disease, such as leaf spot, blight, or blotch, should 

 be sprayed annually until the disease is brought under control. 

 Spraying annually with an insecticide is necessary to control 



