October 2023 - 11

PGRs
The appropriate application method and solution
concentration of the different active ingredients varies.
Foliar sprays can be used to apply any GA-inhibitor, as
they are all taken up by the shoot in leaves (ancymidol,
daminozide, chlormequat chloride) or stems (flurprimidol,
paclobutrazol and uniconazole). Relatively speaking,
daminozide has is the most forgiving active ingredient,
which is why it will have the highest recommended
concentrations (i.e. 1,250 to 5,000 ppm). Chlormequat
chloride has a bit more active compared to daminozide
and recommended spray rates are a little less than half
(750 to 3,000 ppm) than those for daminozide. The
strongest active ingredients are the " triazoles " - ancymidol,
flurprimidol, paclobutrazol and uniconazole.
In addition to the site of uptake and degree of activity
and affecting what application method and concentration
to use, it is important to try and learn about any nuances
specific to the crops you are producing that can influence
PGR choices. For example, daminozide is an effective active
ingredient that can be applied as a foliar spray throughout
the entire production period for potted kalanchoe and
florist chrysanthemums.
For poinsettia, daminozide is also an effective PGR for
controlling height. However, daminozide applications need
to be stopped at the start of short days to avoid negatively
influencing bract development. During short days,
chlormequat chloride can continue to be sprayed until the
start of bract coloration, after which it also cannot be used
any longer due. For the rest of the production phase, lowdose
drenches of paclobutrazol are useful for controlling
unwanted elongation.
ETHEPHON
Ethephon (Collate, Florel, Pistil) is the Swiss Army knife
of PGRs. When applied to plants, the ethephon is taken
up and once inside the plant cell it starts to generate
ethylene. There are several different plant responses to
ethylene and we take advantage of these when utilizing
ethephon. First, ethylene inhibits cell elongation, and
ethephon is commonly used to control height of crops
including potted daffodil and hyacinth. Ethylene can also
reduce apical dominance and increase branching. Using
ethephon to promote branching in poinsettia is called the
" Florel Sandwhich, " it is sprayed three to five days before
pinching, and then again three to five days after pinching.
When flowers are exposed to ethylene it can promote
senescence and abscission; using ethephon early in the
production cycle to inhibit unwanted premature flowering
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October 2023

Table of Contents for the Digital Edition of October 2023
