26 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



year may be caused by grade changes of the earth near the tree, 

 limited space for root growth, girdling roots, root injury from 

 excavation or other soil disturbances, or root diseases. A shovel 

 is useful for making examinations for various root troubles. 



TREE THERAPY 



Spraying, pruning, feeding, watering, and sanitation are 

 used in combating tree diseases. Some diseases may be avoided 

 by use of resistant or immune varieties of trees. 



The effectiveness of a spray may be increased by elimination 

 of the source of the infectious agent that the spray is designed 

 to control and by removal and burning of diseased twigs and 

 branches. Removal of a few trees in dense plantings, to increase 

 aeration, may aid in controlling some diseases. Trees severely 

 weakened by repeated attacks of disease may be given plant food 

 to stimulate vigorous growth. 



Since many diseases controlled by fungicides do not cause 

 serious damage each year, it is not necessary to spray annually 

 for their control. For this reason, the spray chart at the end of 

 this circular (Table 1) does not represent a spray schedule to be 

 followed each year. It is given to show the relationship between 

 the time of year and the approximate time at which sprays should 

 be applied for control of certain tree diseases under Illinois con- 

 ditions. The diseases are listed in the order in which they occur 

 during the growing season. Since sprays are applied to the sur- 

 faces of plants, they act as barriers or protectants against germs 

 and are of major importance against leaf diseases. Equivalent 

 measurements for small quantities of spray are given in Table 2 

 (end of circular). 



Spray Materials 



Most sprays contain materials poisonous to man and other 

 animals and should be used in the manner and at strengths 

 recommended by the manufacturer or as specified in Table 1 

 (end of circular). 



Copper Sulfate and Hydrated Lime. — In combination with 

 water commonly called Bordeaux mixture. Copper sulfate can 

 be purchased as crystals, granules, or powder. The powder is 

 most convenient for use in spray mixtures. 



The instant method of mixing Bordeaux is commonly used. 

 To prepare 100 gallons of an 8-8-100 formula of spray, fill the 

 sprayer tank two-thirds full of water. Start the agitators and 



