Plant growth regulator. That may sound
scary to some, and counterintuitive to others. Why would we want to
intentionally stop a tree or shrub from growing, and how does that even work?
Believe it or not, there are many reasons why it may be beneficial to
slow the growth of a plant, which include economic factors, environmental
factors, and overall plant health factors.
Before we delve in to the specifics of plant
growth regulators, or as I like to call them ‘plant growth managers (PGMs),’
it’s important to know that many of us come in contact with this technology
quite often. PGMs first became popular in the floriculture industry to
get uniform plants that would be merchantable when they made it to the garden
centers. Have you ever noticed your house plants start becoming leggy and
a bit yellow after they’ve been in the house for a few weeks? That is
because the growth regulator applied before you bought them is wearing off.
Early versions of PGMs, Type I growth
regulators, were closely related to herbicides, and actually blocked cell
division to accomplish reduced stem elongation. While Type I growth
regulators work very well at reducing growth there can be some unintended
consequences of using them. Namely, Type
I growth regulators may cause leaf yellowing and distortion. If applied above certain temperatures Type I
growth regulators may also cause slight defoliation.
Modern PGMs, Type II growth regulators, work
within the plant to regulate the hormone (gibberellin) which is responsible for
cell elongation. This means the plant is still producing the same amount
of cells, leaves, buds, etc. just those stems are extending 30%-70% less than
normal. This reduction in growth can lengthen time between pruning cycles
for trees and shrubs growing in close proximity to infrastructure. For example, the oak tree planted 10-feet
from the corner of your executive building, the line of trees planted
underneath those utility lines, or that hedge that needs to be trimmed a few
times a year so you can see out of the first floor windows.
Less pruning means less wounding for the plant
(bonus for the plant), less time your crews need to spend managing your shrub
and tree resources (bonus for labor), and also means less ‘green-waste’ your
crews need to dispose of (bonus for the environment). In 2016, Rainbow
Scientific, in cooperation with our partners, performed a series of trials to
determine labor savings when incorporating Trimtect into their pruning
operations. Trimtect is a foliar spray-applied
Type II plant growth regulator. The
sites selected contained highly manicured shrub hedges ranging in length from
50-180 feet long and 4-8 feet tall. Over
a twelve week period we found pruning time was reduced by an average of 62%
when compared to shrub hedges not treated with Trimtect. In another trial we found green waste removed
from the site was reduced by 50% over a 12 week period. Managers and crew leaders involved in the
trials were unanimous in their positive response to the reduced need to
prune. Landscape crews were able to
focus on getting more detail work accomplished (e.g. weeding, flower bed
maintenance, trash removal, etc.), in addition to getting caught up on turf
mowing and edging. They also had less
‘call backs’ and complaints in areas where Trimtect was applied.
While plant growth managers reduce the amount of
above ground growth by 30%-70%, they are also promoting responses in the plant
that can encourage plant health. One positive side effect of growth control is
the stimulation of another plant hormone, abscisic acid (ABA). ABA helps with preventing
cell dehydration, and regulating leaf water loss by allowing stomata in the
leaves to respond faster to drought conditions. When PGMs are applied as
a soil drench we see energy resources being diverted to the promotion of fine
root growth. This allows a tree to mine more resources from the soil, and
increases drought tolerance. PGMs can also increase the amount of
chlorophyll the plants produce. Chlorophyll is, of course, what gives a
leaf its green color, and plays a major role in photosynthesis. Disease
resistance to certain fungal leaf and canker diseases has also been recorded
with the application of PGMs. So, not
only can you employ PGMs as a growth management tool, but they can also be
employed as a plant health care tool.
The use of plant growth managers can often be
overlooked, but when used correctly, can be a substantial tool to help reduce
time spent on pruning while also benefiting plant health. Next time you’re walking through your site
think of those hedges, ground covers, trees, and vines that seem to need
constant attention. Now imagine, instead
of the plants dictating your pruning schedule, you dictate the plants growing
schedule.
