Growth Regulators in Transition By Jim Barrett

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

Recent Chemical Changes

Valent’s Fascination contains a Cytokinin and Gibberellins 4and 7 (GA4+7). It is extremely effective for preventing leaf yellowing andextending flower life in Easter Lilies and other potted and cut lilies. The useof Fascination was rapidly adopted by lily producers. Fascination is also agood example of a product that, when used correctly, is very beneficial, but ifthe application guidelines are not followed, there is the risk of a completeloss of the crop. Since Fascination contains the GA4+7, some have used it topromote growth in plants that are a little too small or where shoots are notelongating rapidly. While this does work, the product that should be used forthis 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 acquiredthe product and reworked the label. ProGibb is now labeled for those situationswhere folks have used it off-label in the past. It is also labeled forstimulating elongation in stunted greenhouse crops. An example of where ProGibbcould be beneficial is garden mums that might be finishing a little short orthe flowers may be staying too tightly bunched. In this situation, a lightspray to give 1/2-2 inches of elongation could be beneficial. Another use forProGibb is to reverse the effects of an over-application of a growth retardant.

If ProGibb sounds too good to be true, well, there aredownsides to everything. ProGibb is probably the most active growth regulatorwe have, and it is very easy to cause excessive stretching. A good strategy forProGibb to promote stem elongation is to spray at a very low rate and reapplyif 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. Iftoo 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 usedin some other applications.

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

An interesting evolution has been the recent rush to useFlorel on poinsettias. This corresponded with the introduction of thepoor-branching ‘Winter Rose Dark Red’ as an important novelty variety. WinterRose creates a finished plant with shoots at staggered heights. Thisnon-uniform plant appearance goes against everything most growers try to dowith poinsettias. Florel applications 3-7 days before and 3-7 days after thepinch (termed the “Florel sandwich”) will create a more uniformlybranched Winter Rose and a more typical poinsettia appearance. However, my discussionswith consumers, who do not know the industry’s image of a poinsettia, indicatethat they actually prefer the non-uniform plant because of its noveltyappearance. Oh well, what do they know? For other varieties similar to Freedomand Orion, Florel will reduce the initial shoot elongation after the pinch andoften promote more uniform branching. This branching problem with Freedom andOrion will be fixed by replacing them with the new generation of varieties thatare now in testing.

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

Upcoming Chemical Changes

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

SePRO is developing Topflor and is expecting EPA clearancesometime in 2003 or 2004. Topflor is very active, similar to Bonzi, and will beused in a similar manner. Research on Topflor is being conducted at severaluniversities, and we will be seeing more reports on it at various growermeetings. 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, andthose experimental compounds became Bonzi, Sumagic and Topflor. Due to variousbusiness 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 learnthe name Paclobutrazol. Paclo, as I shorten it, is the active ingredient inBonzi, and there will be one or more new Paclo products introduced sometime in2003. Through the summer and early fall, there have been heavy discussionsamong 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. Growersare likely to notice a little more competition for their business betweencompanies that are supplying Paclo products and other PGRs. As a researchervery interested in product and information development, I hope a part of thatcompetition leads to more emphasis on developing new information about uses ofPaclo and the other products.

Application Changes

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

Bedding plant growers are injecting the PGR into theirrigation water and applying a drench to flats similar to the way they would fertilize.This type of drench is called “watering in” or the “feedmethod.” This procedure is very easy, and there is not much of a learningcurve, since workers already know how to water or fertilize the crop.

It is amazing the way the industry is utilizing the widevariety of vegetative annuals in baskets and combination containers; however,many of these varieties often have very strong vigor, which can become aproblem when we try to grow them in smaller containers or when they becomeovergrown. A new procedure, called a “liner dip” or “linerdrench,” refers to the liners or plugs being treated prior totransplanting. This can be done by drenching the chemical over the top ordipping the liner tray in the chemical (only the media needs to be dipped). Thegrowth regulator will greatly reduce the initial growth of the plant aftertransplanting. For combination containers, only the most vigorous liners needto be treated.

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

Jim Barrett

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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