l88 PLANT GROWTH SUBSTANCES 



desirable results with certain additives to the salts of 2,4-D the esters 

 are largely used today in right-of-way vegetation control because day 

 in and day out they are the most effective formulations we have for the 

 general run of species, regardless of rainfall subsequent to application. 

 It must be remembered that in right-of-way control many crews must 

 operate continuously over a period of several weeks and a formulation 

 or a chemical must be versatile in its action. 



Brush regrowth from woody plants that have periodically been cut 

 off, sometimes for many years, constitutes the chief problem on a utility 

 right-of-way in areas of moderate to heavy rainfall. Experience has 

 shown that spraying may be successfully carried out from about the time 

 the leaves are fully developed until late summer. This is not in conflict 

 with the general concept that plants should be in an active state of 

 growth for best results with 2,4-D. Except under very dry conditions 

 such woody plants are growing actively throughout the summer months. 

 Experience has shown that spraying before the leaves have fully de- 

 veloped will often result In Inferior kills. This appears to agree with the 

 concept that 2,4-D Is most actively translocated from leaves to stems 

 in association with carbohydrate movement. 



It soon became apparent in the early work with 2,4-D on woody 

 plants that many species were highly resistant. In the summer of 1946 

 an old mountaineer in West Virginia told me that the best blackberries 

 he picked that summer were on the right-of-way that had been sprayed 

 the year before. We had eliminated most of the competing woody species. 

 Because blackberries and other members of the genus Rubus are so 

 widespread the entire program for a time appeared discouraging. It takes 

 no ecologlst to see that eliminating competing plants would enable a 

 species hke blackberry to take over an area. 



Screening of a number of compounds related to 2,4-D on blackberry 

 and other resistant species was carried out and 2,4,5-trichlorophenoxy- 

 acetic acid (2,4, 5-T) was found to be specific for some of them, particu- 

 larly members of the genus Rubus. During the past two years much of 

 the woody plant control on rights-of-way has been carried out with a 

 mixture of 2,4-D and 2, 4, 5-T. Admittedly this Is a shotgun treatment 

 and at times one or the other component might prove best, but until 

 we know more about how species respond and until the spray operators 

 know more exactly the species with which they will have to contend the 

 mixture appears to be desirable. Not all undesirable woody species are 



