16 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 53 



and must be handled with care and as directed by the manufacturers. 

 The amount of spray apphed should be kept to an effective mini- 

 mum — for an average 50-foot elm, 2-3 gallons of spray if a mist 

 blower is used and 20-30 gallons if a hydraulic sprayer is used. 



Watering places, feeding stations, and other places frequented 

 by birds, as well as fish ponds, should be protected from spray drift 

 and runoff. It is recommended that bird baths be cleaned following 

 spraying, and that the collection of spray in puddles, likely to occur 

 where hydraulic sprayers are used, be eliminated. In spite of these 

 precautions, it is probable that some birds will be killed, especially 

 robins early in the season. 



Killing Grafted Roots 



Wherever elms are close enough together (up to 35 feet apart) 

 so that root grafts occur, the Dutch elm disease fungus can pass from 

 diseased to healthy trees. This spread of the fungus can be prevented 

 by killing segments of roots with SMDC (32.7 percent sodium me- 

 thyldithiocarbamate), available commercially as Vapam or VPM. 

 For most effective results the chemical must be applied as soon as a 

 diseased tree shows earliest wilt symptoms. 



Treating with SMDC consists of placing the diluted chemical 

 (1 part chemical and 3 parts water) in ^-inch holes in the soil, 15 

 inches deep and 6 inches apart, in a straight line equidistant between 

 trees (Fig. 15). The holes can be made with a ^^^-inch auger bit or 

 other suitable equipment. For effective control, the line of holes must 

 be long enough to include all grafted roots, usually 15 or more feet. 

 However, the line of holes should be at least 10 feet from the trunk 

 of the healthy tree. About Yi cup of the liquid is placed in each hole. 

 It is suggested that the chemical be poured into the holes slowly and 

 carefully, to keep turf injury to a minimum. As soon as the chemical 

 is dispensed the hole is closed by tamping to prevent loss of vapors. 



When obstructions such as pavement or plant material prevent 

 application of the chemical in a straight line, the pattern of holes 

 can be varied to fit the circumstance, as illustrated in Fig. 15. 



The diseased tree should not be removed for 2 weeks after 

 treating. This will allow adequate time for the sap to stop flowing 

 through the poisoned root sections. Upon removal, the tree must be 

 burned as described under "Sanitation." 



Treating with SMDC causes very little disturbance of turf since 

 the circle of grass killed around the holes is only 3-6 inches in di- 

 ameter. These dead areas can be reseeded or resodded 4-6 weeks 

 after the chemical is applied. Also, this method of treating is easy 

 and inexpensive, and does not damage underground cables, pipes, 

 and other objects. 



