In the first article of this series, we discussed application considerations and optimal rates of Topflor (flurprimidol) on potted plants. In this article, we focus on spring bedding plants.
Throughout the past five years, we have conducted extensive trials at North Carolina State University and obtained excellent results with spring annuals. Topflor is a new addition to the PGR toolbox and, hopefully, our research trials will provide some insight into how it can work for you.
Ageratum
We trialed Topflor foliar sprays (20, 30, 40, 50 or 60 ppm) and compared those rates with Bonzi (paclobutrazol) at 40 ppm and Sumagic (uniconazole) at 10 ppm on ageratum ‘Hawaii Blue’ grown in 1203 and 1801 cell packs. Topflor applied at 40 ppm resulted in plants that were 21 percent shorter than the untreated control. It should be noted that there was a slight amount of foliar phytotoxicity with 40-ppm Topflor, but the new leaf growth quickly covered it. Topflor at 60 ppm provided comparable height control as 40-ppm Bonzi, and Topflor at 20 ppm was comparable to 10-ppm Sumagic.
Celosia
Topflor was applied as a foliar spray (10, 20, 30, 40 or 50 ppm) and compared with Bonzi at 35 ppm and Sumagic at 5 ppm on celosia ‘Red Glow’ grown in 1203 and 1801 cell packs. Topflor applied at 50 ppm resulted in plants that were 17 percent shorter than the untreated control. Topflor at 20 ppm provided comparable height control as 35-ppm Bonzi, and Topflor at 50 ppm was equivalent to 5-ppm Sumagic.
Seed Coleus
Topflor was applied as a foliar spray (10, 20, 30, 40 or 50 ppm) and compared with Bonzi at 35 ppm and Sumagic at 10 ppm on coleus Á ‘Wizard Golden’ grown in 1203 and 1801 cell packs. Topflor applied at 20 ppm resulted in plants that were 16 percent shorter than the untreated control. Topflor at 10 ppm provided comparable height control as 35-ppm Bonzi, and Topflor at 20 ppm was equivalent to 10-ppm Sumagic. ‘Wizard Golden’ is not a vigorous grower, and lower rates may be appropriate.
Dusty Miller
Topflor was applied as a foliar spray (10, 20, 30, 40 or 50 ppm) and compared with Bonzi at 35 ppm and Sumagic at 10 ppm on dusty miller ‘Silverdust’ grown in 1203 and 1801 cell packs. Topflor applied at 10 ppm resulted in plants that were 28 percent shorter than the untreated control. Bonzi applied at 35 ppm resulted in plants that were 13 percent shorter than the untreated control. Topflor at 10 ppm provided comparable height control as 10-ppm Sumagic. Retail growers may want to conduct trials with rates lower than 10 ppm.
Seed Impatiens
Topflor was applied as a foliar spray (20, 30, 40, 50 or 60 ppm) and compared with Bonzi at 35 ppm and Sumagic at 10 ppm on impatien ‘Accent Carmine’ grown in 1203 and 1801 cell packs. Topflor applied at 60 ppm resulted in plants that were 22 percent shorter than the untreated control. Bonzi applied at 35 ppm resulted in plants that were 30 percent shorter, and Sumagic at 10 ppm resulted in 33 percent shorter plants than the untreated control. Topflor at 60 ppm provided less control than Bonzi at 35 ppm or Sumagic at 10 ppm; therefore, consider trialing multiple Topflor applications as a way of obtaining a greater degree of control.
Marigold
Topflor was applied as a foliar spray (10, 20, 30, 40 or 50 ppm) and compared with Bonzi at 35 ppm and Sumagic at 10 ppm on marigold ‘Antigua Orange African’ grown in 1203 and 1801 cell packs. Topflor applied at 40 ppm resulted in plants that were 12 percent shorter than the untreated control. Topflor at 30 ppm provided comparable height control as 35-ppm Bonzi and 10-ppm Sumagic.
Seed Petunia
Topflor was applied as a foliar spray (20, 30, 40, 50 or 60 ppm) and compared with Bonzi at 40 ppm and Sumagic at 20 ppm on petunia ‘Madness Plum Crazy’ grown in 1203 and 1801 cell packs. Topflor applied at 50 ppm resulted in plants that were 12 percent shorter than the untreated control. Topflor at 40 ppm provided comparable height control as 40-ppm Bonzi and 20-ppm Sumagic.
Salvia
Topflor was applied as a foliar spray (20, 30, 40, 50 or 60 ppm) and compared with Bonzi at 40 ppm and Sumagic at 10 ppm on salvia ‘Splendens Red Hot Sally Deep Red’ grown in 1203 and 1801 cell packs. Topflor applied at 50 ppm resulted in plants that were 15 percent shorter than the untreated control. Topflor at 20 ppm provided comparable height control as 40-ppm Bonzi and 10-ppm Sumagic.
Vinca
Topflor was applied as a foliar spray (21⁄2, 5, 71⁄2, 10 or 20 ppm) and compared with Bonzi at 30 ppm and Sumagic at 5 ppm on vinca ‘Pacifica White’ grown in 1203 and 1801 cell packs. Topflor applied at 21⁄2 ppm resulted in plants that were 43 percent shorter than the untreated control. Topflor rates lower than 21⁄2 ppm may be more appropriate for retail growers. Topflor at 5 ppm provided comparable height control as 30-ppm Bonzi and 5-ppm Sumagic. Vinca has a strong response to Topflor, Bonzi and Sumagic; therefore, growers should be careful to apply correct spray rates to avoid overdoses. Note that Bonzi is not registered for use on vinca, and the rate range for Sumagic is 1-3 ppm.
Summary
Topflor is a new tool for preventing unwanted plant stretch. The rates discussed in this article are a starting point for conducting your own trials. Keep in mind that all results are based on North Carolina growing conditions and will need to be adjusted for other locations, cultivars and times of the year. Typically, growers in more northern areas should start trialing with rates 50 percent less than those listed, and growers in more southern areas should trial rates up to 50 percent higher.
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