January 2024 - 36

PGRs
Annuals and
" W
PERENNIALS
ork smarter, not harder. " If ever there is a time
to keep this mantra at the front of your mind,
the spring season is it. From annual to perennial,
seed to cutting to bare root, flats to 4-inch to large patio
containers and hanging baskets, the spring season literally
has it all - and the " to-do " lists reflect that.
Identifying opportunities to produce crops more
efficiently and effectively should be every grower's goal,
and plant growth regulators (PGRs) are great tools to have
in your toolbox. This article will review how PGRs can be
used to improve rooting and cutting quality in propagation,
suppress or promote growth, enhance branching and delay
flowering of annual and perennial crops.
AUXIN
There is no denying the increasing popularity of
vegetatively propagated bedding plants. The number of
annuals and perennials produced from rooted stem-tip
cuttings is evident when looking at what is grown in
4-inch and 1-gallon pots, as well as hanging baskets and
other mixed containers. To promote uniform and timely
rooting of cuttings for these species and cultivars, rooting
hormones are commonly applied at sticking. The most
widely used rooting hormone, indole-butyric acid (IBA), is
usually suspended in a talcum powder or a liquid solution
into which the basal end of cuttings are dipped in before
being stuck into liner trays or, in some instances, directly
into finishing containers (i.e. zonal geraniums). Newer IBA
formulations now make it possible for growers to apply
rooting hormone as a foliar spray to cuttings after they
have already been stuck.
Why spray rooting hormone instead of using dips? Time
and money. The primary advantage to using foliar sprays
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JANUARY 2024 GPNMAG.COM
PART 2
The PGR Toolbox provides resources to improve quality and efficiency in crops
BY CHRISTOPHER J. CURREY
as opposed to basal dips is the labor savings. Although
it only takes a fraction of a second to dip a cutting into
rooting hormone, that adds up when thousands and
thousands of cuttings arrive for sticking.
If you are new to foliar auxin sprays, don't use
concentrations recommended for dips for foliar
sprays - it will likely be excessive and damage plants.
Concentrations appropriate for sprays are much lower
than those used for dips, as low as 80 to 400 ppm for
foliar sprays compared to ≥1,000 ppm for dips.
Typically, 2 quarts of final solution are applied per
100 square feet of growing area, and this works well for
foliar auxin sprays, too. However, although not necessary,
applying higher volumes of auxin spray allows for runoff
from the heavy application volume to end up at the base
of the stem and further enhances root promotion.
GIBBERELLIC ACID INHIBITORS
Controlling plant growth and unwanted stretch
is an important part of spring crop production. The
most common PGRs applied to control growth are the
gibberellic acid (GA) synthesis inhibitors. By reducing
GA synthesis, plant cells elongate less and growth is
suppressed. Ancymidol (Abide, A-Rest), chlormequat
chloride (Altercel, Citadel), daminozide (B-Nine, Dazide),
flurprimidol (Topflor), paclobutrazol (Bonzi, Piccolo,
Paczol) and uniconazole (Concise, Sumagic) are all the
different GA-inhibitors labeled for use on spring crops.
One of the biggest differences between these active
ingredients is their relative strength. For daminozide
sprays, 2,500 or 5,000 ppm are common and appropriate
concentrations, whereas uniconazole sprays may only be
a few (<5) ppm. The residual activity of these compounds
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January 2024

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