Keeping the Right-Of-Way Clear – With Science

It’s spring storm season, and one thing we’ve learned is that trees and weather don’t always mix. Part of providing reliable power to our members involves line clearance and FreeState does that with in-house right-of-way crews. These crews are an essential part of keeping the lights on, and you’ll learn more about that in the next pages, but we want to take the opportunity to highlight one specific tool in our arsenal for vegetation management.  

As part of the right-of-way clearance program, FreeState tree crews have started using a Tree Growth Regulator (TGR) Paclobutrazol program. While fairly new to the co-op, it is an established practice with a solid history in the line clearance industry.  

When applied, TGR can lengthen the amount of time between trim cycles of valued trees in our area landscape helping to keep the lines clear even longer.  

How does it work? 

Tree growth is regulated by the hormone, gibberellin. TGR inhibits the production of gibberellin that promotes the lengthening of new cells produced at the ends of twigs. Even with the application of TGR, cell production still occurs, but they do not elongate. Instead, the same number of leaves and new growth points are packed into a much shorter length. By shortening the growth near energized conductors, the tree can remain without causing an issue with reliability.  

Can it hurt my tree? 

TGR is slow moving when applied to the soil and the impact on any neighboring vegetation is miniscule. What you may see at the base of the tree is grass or flowers with shorter growth, too.  

What is most noticeable after application is the reduction of overall new leaf size with a slightly darker color. The darker color is a rich green due to the concentration of chlorophyll in the smaller leaves. This color change is an indication that the leaves are continuing to feed the tree.  

Stimulation of root growth can also be observed in treated trees. Fine root density can increase by 60-80% in some oak trees near the base. This increase in root growth, along with an enhanced ability of the leaves to reduce the loss of water during transpiration, has even shown some trees to have elevated drought tolerances. 

When TGR is applied at recommended dosage, it has been shown to be very safe, and in fact sometimes beneficial to trees. The use of TGR is evolving from being applied to trees solely as a treatment under utility lines to use by commercial landscapers and arborists because of its growth suppression and other tree health benefits. 

What can I expect to see during application? 

The application process is quite simple. If your tree is determined to be a candidate for this program, FreeState will set up a time to treat your tree, either before or after trimming. If treatment is done before trimming, the regrowth response of the tree will be reduced. If some regrowth is desirable after trimming, we can delay the treatment, so the tree has time to produce some normal growth before being suppressed. This may soften the look of a freshly trimmed tree, particularly if the trimming needed was significant.  

During application we will dig a small trench around the base of the tree at the root flare. A premeasured amount of the chemical is mixed with water based on the size and type of tree being treated. This mixture is poured evenly around the base of the tree in this trench until all is absorbed. The dirt is replaced at the base of the tree and treatment is complete. Following treatment, we will revisit your tree periodically to monitor its growth. Treatment can be expected to last for three years.