Greenhouse and Nursery - Topflor, a New Plant Growth Regulator

One of the newer growth regulators available to greenhouse and nursery producers is Topflor. The following is an article on research using Topflor.

Plant growth retardants (PGRs) are commonly applied to container-grown plants to control stem elongation and produce high quality, compact plants. Flurprimidol (SePRO, Carmel, Ind.) was a molecule discovered over 20 years ago by Eli Lily and Company. It is a “Type 2” PGR, similar in its mode of action to A-Rest, Bonzi, and Sumagic. Flurprimidol has been labeled as Cutless for turf use in the U.S. and commercially introduced as Topflor in Europe for greenhouse crops. Cutless has been trailed extensively on nursery crops such as butterfly-bush (Keever and Gilliam, 1994), holly (Keever et al., 1994), and Mexican sage (Burnett et al., 2000) with growth control comparable to Bonzi and Sumagic.

Even though the initial Topflor trials were conducted in the United States on poinsettia, exacum, and pot chrysanthemum, the chemical was not introduced to the U.S market. In Europe, Topflor has been extensively trailed since the early 1990’s on a number of greenhouse plants such as chrysanthemum (Pobudkiewicz and Nowak, 1997), dianthus (Pobudkiewicz and Nowak, 1994), osteospermum (Olsen and Andersen, 1995), and streptocarpus (Pobudkiewicz, 2000). Commercial recommendations for applying Topflor foliar sprays to a number of greenhouse crops have been developed for European growers.

In Europe, a 1.5% Topflor formulation is used, while the new formulation that will be available in the U.S. is 0.38%. With reformulating Topflor, it has not been tested under U.S. growing conditions or on cultivars available in North America. Research is currently being conducted at a number of universities: North Carolina State, Purdue, Virginia Tech, University of Florida, and Cornell. The goal has been to determine optimal application rates for U.S. conditions. The following are research findings from the Southeast trials conducted at North Carolina State University and the Midwest trials conducted by Dr. P. Allen Hammer and Terri Kirk at Purdue University.

Foliar sprays of Topflor controlled growth of New Guinea impatiens. Southeastern U.S. growers should begin with 2.5 to 5 ppm sprays. Rates may vary by location and cultivar.

Topflor foliar sprays are effective in controlling growth of of pot mum sprayed once or sprayed twice,with the second spray applied 2 weeks after the first. Rates are between 10 and 30 ppm.

Substrate drenches of Topflor were an effective means of controlling "Ellen Houston" tuberous dahlia growth. Southeast U.S. growers should begin with 1 to 2 mg a.i./pot drenches. Rates may vary by location and cultivar.

Under Indiana growing conditions, Topflor foliar sprays of 80 ppm were required to control Easter lily growth. At 160 ppm, lower leaf yellowing occurred in North Carolina. Additional research is required to determine optimal rates.

Topflor foliar sprays of 5 ppm provided comparable growth control for fall pansies as Bonzi at 10 ppm, A-Rest at 10 ppm, or Florel at 50 ppm. Sumagic at 2.5 ppm provided a greater degree of growth control. The cultivar tested was Majestic Giants Yellow Blotch.

Topflor foliar sprays provide excellent growth control for bedding plants. Topflor rates of 2.5 ppm controlled growth of Pacifica White vinca grown in 1801 cell packs. Silverdust dusty miller growth was controlled with 10 ppm of Topflor when grown in 1203 cell packs.

Topflor foliar sprays provided growth control of zonal geraniums. For the less aggressive cultivar Samba, rates of 20 ppm applied once or 15 ppm applied twice (with the second application occurring 2 weeks after the first). Higher rates of 30 ppm applied once or 20 ppm applied twice also worked well for the more aggressive cultivar Noblesse 99. Rates may
vary by location and cultivar.

The response of Orion poinsettias to Topflor foliar sprays varied by location. Optimal rates appear tobe 2.5 to 5 ppm for Indiana and around 35 to 40 ppm for North Carolina. Additional research is required to determine optimal rates.

Both foliar sprays and substrate drenches of Topflor controlled growth of Pacino pot sunflowers. These plants flowered in January and slightly higher rates may be required for Southeastern U.S. locations during other times of the year. Rates may vary for other locations.

Information from Horticulture Research Series No. 156, Topflor: A New Plant Growth Regulator by Brian E. Whipker, Department of Horticultural Science, North Carolina State University, Raleigh, NC. For the full article with pictures go to http://www.pgrinfo.com/