ipO PLANT GROWTH SUBSTANCES 



are covered with a dense grass sod after two years of spraying. Apparently 

 grass and grass seed were present in sufficient amounts to permit it to 

 become established once the competing woody plants and tall-growing 

 herbaceous species were eliminated. Where species predominate which 

 are stunted but not killed by the available herbicides a mixed grass 

 and shrub community can apparently be maintained without the woody 

 plants growing excessively large. 



During the present season there were many thousands of miles of 

 utility rights-of-way sprayed with the chlorophenoxyacetic acids. This 

 is definitely not a one-season program. One treatment will not result in 

 the eradication of many plants. The general practice at present appears 

 to be to spray woody regrowth up to ten feet tall during the summer 

 and then make a second application the next year. Cost of each of these 

 sprays in many cases is no more than the cost of a single cutting with 

 scythes or brush hooks. After two consecutive years of spraying a third 

 year may be skipped and in some cases the fourth year. It appears that 

 a continuous maintenance program will require respraying at intervals 

 of about three years, depending, of course, on rainfall and species 

 composition. The utilities that have been in this program the longest 

 now conservatively estimate that they are cutting the cost of maintaining 

 their rights-of-way in half. 



An interesting recent development in vegetation control is the appli- 

 cation of 2,4-D and 2,4,5-T to the bark of woody plants and to cut 

 surfaces of stumps (2). Absorption varies with the species and no doubt 

 with many other conditions; however, good kills have been obtained 

 from application during all seasons of the year. Dormant season applica- 

 tion offers the possibility of extending operations to make more con- 

 tinuous use of labor and also may make possible the use of these herbicides 

 on rights-of-way in areas where highly sensitive crops preclude summer 

 foliage spray application. 



Highway departments have much the same problem with respect to 

 woody vegetation, and their methods of operation are similar. They must 

 use even greater care, however, with respect to plants on adjoining 

 properties because so often highways transverse populated areas. Much 

 of the utility right-of-way spraying is in mountainous country where 

 there are few crops near by. In addition to spray-gun operations for 

 woody plants some highway departments are using spray booms to 

 advantage, treating the entire area from the edge of the road to the 



