February 2025 - 14

CEA
crops, while submerging cuttings in a rooting hormone
solution is effective at promoting roots over an
untreated control.
Microdrench
You may be quite familiar with PGR drenches - an
application of a relatively large volume of a PGR solution
at a low concentration to the growing substrate. It's a
much lower rate than what would be applied as a spray.
With a PGR microdrench application, rates are further
reduced compared to a traditional drench by about
one-tenth to an eighth. That means more applications
throughout production, usually about three to four. An
advantage of microdrenching is less risk of stunting crops
and delaying flowering, along with reduced residual effect
for consumers.
If you are interested in trialing microdrenches, here are
a few guidelines to help along the way:
* Start the first application anywhere from 7 to 10 days
after transplant. This is generally the most costeffective
time because you really want those roots
to have grown since the PGR is being applied to the
growing substrate.
* If you're using subirrigation, reduce the amount of
PGR by about 25% to 50% compared to the PGR
drench rate.
* If you use bark in your substrate, slightly increase
that rate because bark can bind or hold up the PGR.
* Always conduct your own trials on a small scale to
determine appropriate PGR rates for the crops that
you're growing as well as the specific conditions of
your greenhouse.
ETHEPHON EFFECTS
Ethephon is a great product to produce more compact
plants as it increases branching. Ethephon is applied as a
liquid, but in the greenhouse it turns into the active form
of ethylene gas that plants can absorb, as it's a natural
plant form. Ethylene is typically known as a senescence
hormone, but really it suppresses stem elongation by
reducing apical dominance so the plant produces more
branches instead of growing upward.
In some instances, ethephon will set the flowering clock
back to zero. For example, a crop of New Guinea impatiens
showed a few plants with flowers, but the flower set was
too early in the production cycle. Applying ethephon now
induces abscission or abortion of those flowers and buds,
and sets the clock to zero so all the impatiens come into
flower at the same time.
Best practices
A big win for ethephon is the inexpensive cost compared
to other PGRs, although the biggest complaints from
14 FEBRUARY 2025 GPNMAG.COM
Ethephon is a
great product to
produce more compact
plants as it increases
branching.
greenhouse growers have been the inconsistent results
seen from one application to the other.
A study took shape to determine the causes of
inconsistency. Was it the water quality, varying
environmental conditions in the greenhouses or
application challenges? Two ethephon products from Fine
Americas were used in this study: Florel and Collate.
It's important to note that while these two products
have the same active ingredient, the concentration of
ethephon varies greatly and each will require different
amounts when preparing your solution. In addition, the
amount of Florel or Collate that is added to the solution
can change the pH, reducing its effectiveness.
pH
Previous research revealed the evolution of ethephon
to ethylene increases as the spray solution pH increases
above 4.5. Therefore, if the water you're mixing with has
a high pH, the ethylene is released right from that liquid
to a gas, and the plant can't take it in quickly enough. If
the spray solution pH is too low, the plant will take a lot
of that ethylene, and now there is a potential for product
phytotoxicity in some species.
Collate and Florel are acidic, so check product labels
for the final recommended solution pH. This is the target
number you want your solution to read before applying to
plants to get the best effectiveness from your application.
Temperature
Ethephon product labels often recommend an
application temperature range of 60° F to 95° F, but
previous research has shown this is not optimal. Ethephon
breaks down very slowly at low temperatures (plants take
up ethylene slowly) and quickly at high temperatures
(plants can't take up all the ethylene in the time it's
available).
THE NEW STUDY
Developed to determine how the carrier water alkalinity
and the ambient air temperature at application affected
the efficacy of ethephon sprays, this study used four
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February 2025

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