Growth Regulators in Transition

November 5, 2002 - 14:07

For the first time in years, there are new PGRs on the market and in development. Here are the basics to keep you up-to-date.

Over the past several years, there have been few changes in
the growth regulators available to the greenhouse industry. While there have
been many new insecticides and fungicides introduced, we have been working with
the same height control products, but this might not be a bad thing. The
application of PGRs is generally more exacting than most other types of
chemicals. The lack of evolution in the PGR products has actually been good for
growers since they have had the opportunity to become very familiar with the
products they use without having to learn new ones. However, changes in the
available chemicals started a couple of years ago and will continue for at
least a couple of more years.

Recent Chemical Changes

Valent's Fascination contains a Cytokinin and Gibberellins 4
and 7 (GA4+7). It is extremely effective for preventing leaf yellowing and
extending flower life in Easter Lilies and other potted and cut lilies. The use
of Fascination was rapidly adopted by lily producers. Fascination is also a
good example of a product that, when used correctly, is very beneficial, but if
the application guidelines are not followed, there is the risk of a complete
loss of the crop. Since Fascination contains the GA4+7, some have used it to
promote growth in plants that are a little too small or where shoots are not
elongating rapidly. While this does work, the product that should be used for
this purpose is ProGibb.

ProGibb, which contains GA3, has been around for many years,
but it was not labeled for use on greenhouse crops. Valent recently acquired
the product and reworked the label. ProGibb is now labeled for those situations
where folks have used it off-label in the past. It is also labeled for
stimulating elongation in stunted greenhouse crops. An example of where ProGibb
could be beneficial is garden mums that might be finishing a little short or
the flowers may be staying too tightly bunched. In this situation, a light
spray to give 1/2-2 inches of elongation could be beneficial. Another use for
ProGibb is to reverse the effects of an over-application of a growth retardant.

If ProGibb sounds too good to be true, well, there are
downsides to everything. ProGibb is probably the most active growth regulator
we have, and it is very easy to cause excessive stretching. A good strategy for
ProGibb to promote stem elongation is to spray at a very low rate and reapply
if needed. One can see the effects of ProGibb within 3-5 days. So, use 2-3 ppm,
and if the plants have not moved in a few days, make another application. If
too much is put on, in five days the plants might be too stretched to be salable.
Note that these rates are considerably below the 50-250 ppm ProGibb rates used
in some other applications.

Florel, or Pistil, contains ethephon, and its use has
expanded dramatically in the past few years. It is useful for knocking off
early flowers and promoting branching in a number of crops. A word of caution
here -- Florel has a narrow, crop-specific label with a 48-hour REI, and it is
often used outside of label recommendations.

An interesting evolution has been the recent rush to use
Florel on poinsettias. This corresponded with the introduction of the
poor-branching 'Winter Rose Dark Red' as an important novelty variety. Winter
Rose creates a finished plant with shoots at staggered heights. This
non-uniform plant appearance goes against everything most growers try to do
with poinsettias. Florel applications 3-7 days before and 3-7 days after the
pinch (termed the "Florel sandwich") will create a more uniformly
branched Winter Rose and a more typical poinsettia appearance. However, my discussions
with consumers, who do not know the industry's image of a poinsettia, indicate
that they actually prefer the non-uniform plant because of its novelty
appearance. Oh well, what do they know? For other varieties similar to Freedom
and Orion, Florel will reduce the initial shoot elongation after the pinch and
often promote more uniform branching. This branching problem with Freedom and
Orion will be fixed by replacing them with the new generation of varieties that
are now in testing.

When applying Florel to poinsettias it is very important to
remember that it provides reduced stem elongation and to not use other PGRs at
that time.

Upcoming Chemical Changes

All of the chemicals in the B-Nine, Cycocel, A-Rest, Bonzi
and Sumagic group have increased in use over the past 5-8 years, but Bonzi use
has grown the most, by far.

SePRO is developing Topflor and is expecting EPA clearance
sometime in 2003 or 2004. Topflor is very active, similar to Bonzi, and will be
used in a similar manner. Research on Topflor is being conducted at several
universities, and we will be seeing more reports on it at various grower
meetings. Topflor will be new to the industry, but it is not a new chemical.
Simultaneously, in the early '80s, we were looking at three very active,
unnamed compounds from different chemical companies for their potential, and
those experimental compounds became Bonzi, Sumagic and Topflor. Due to various
business decisions, Topflor was introduced in Europe and not the United States.
Now that SePRO has acquired the chemical, it will be made available here.

Another change on the PGR horizon is that growers will learn
the name Paclobutrazol. Paclo, as I shorten it, is the active ingredient in
Bonzi, and there will be one or more new Paclo products introduced sometime in
2003. Through the summer and early fall, there have been heavy discussions
among chemical companies to work out who will be handling which Paclo products.
However, who makes or who sells a product is of little concern to most growers,
as long as the product is available and use information is available. Growers
are likely to notice a little more competition for their business between
companies that are supplying Paclo products and other PGRs. As a researcher
very interested in product and information development, I hope a part of that
competition leads to more emphasis on developing new information about uses of
Paclo and the other products.

Application Changes

Another PGR transition occurring in the industry is in
methods used to apply some PGRs. A-Rest, Paclo (Bonzi) and Sumagic (and
eventually Topflor) are better applied through the media; there is greater
uniformity, less chance of over stunting and less effect on flower development
when applied this way. Several application procedures have evolved to take
advantage of media uptake. The accompanying pictures illustrate some of these.

Bedding plant growers are injecting the PGR into the
irrigation water and applying a drench to flats similar to the way they would fertilize.
This type of drench is called "watering in" or the "feed
method." This procedure is very easy, and there is not much of a learning
curve, since workers already know how to water or fertilize the crop.

It is amazing the way the industry is utilizing the wide
variety of vegetative annuals in baskets and combination containers; however,
many of these varieties often have very strong vigor, which can become a
problem when we try to grow them in smaller containers or when they become
overgrown. A new procedure, called a "liner dip" or "liner
drench," refers to the liners or plugs being treated prior to
transplanting. This can be done by drenching the chemical over the top or
dipping the liner tray in the chemical (only the media needs to be dipped). The
growth regulator will greatly reduce the initial growth of the plant after
transplanting. For combination containers, only the most vigorous liners need
to be treated.

Another new application method is to use spray equipment and
apply the PGR to the media at planting, which is referred to as a "media
spray" or "media sprench." This can be used on plugs, where it
is very useful on crops that have significant early stretch. The best strategy
with plugs is to spray after they are put out in the greenhouse but before or
soon after emergence. Media sprays are useful on plugs and liners at
transplant, also. Often, the easiest procedure here is to apply the chemical a
day or two after transplanting. At this stage, there is a large amount of media
surface exposed, so most of the spray will enter the media and act like a

About The Author

Jim Barrett is professor of floriculture at the University of Florida and GPN's consulting editor. He may be reached at by phone at (352) 392-1831 x248 and E-mail at

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