52 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



the two summer sprays recommended for phloem necrosis con- 

 trol (Table 1). Sanitation (the removal and burning of all weak- 

 ened, dying, and recently killed elm material) is exceedingly 

 important where both diseases occur, because elms killed by 

 phloem necrosis as well as by Dutch elm disease provide excellent 

 breeding places for the smaller European elm bark beetles that 

 carry Dutch elm disease fungus from diseased to healthy trees. 



ii**. 



Fig. 49. — Hydraulic sprayers used in spraying elms with methoxychlor 

 or DDT for control of the insect that spreads phloem necrosis must have 

 sufficient power to give thorough coverage of all parts of trees. Drenching 

 that results in excessive run-off should be avoided. 



