Super Elfin Lavender Impations were left untreated (left), drenched with 0.5 ppm Topflor every other week (middle) and drenched with 0.5 ppm Topflor every week (right).
Photos taken by Dr. Brian Whipker of North Carolina State University, courtesy of Mark Brotherton.

In experimenting with plant growth regulator (PGR) application methods, growers have found success with several different methods, including foliar sprays, preplant soaks and dips, and both drenches and more fine-tuned processes such as micro drenches. Many growers are turning to SePRO products, such as Topflor and A-Rest, and seeing the desired results.

Plant growth regulator research

“Growth regulators – PGRs – we generally think of those as chemicals that will cause certain responses in plants,” says Dr. Bill Miller, professor of floriculture in Cornell University’s Department of Horticulture. “Most of the PGRs that we use in floriculture are used to keep plants shorter.”

Various PGR formulas have different effects, Miller says. Some – such as Topflor and A-Rest from SePRO – inhibit gibberellin production, others release ethylene, others reduce bud dormancy and others inhibit leaf yellowing.

Growers can see numerous benefits from making PGR applications using a micro drench method, says Mark Brotherton, portfolio leader at SePRO. The concept implies applying PGRs at a lower rate and often earlier and more frequently than regular drench applications. “Micro drench rates are generally 1/10 that of what growers would use in [each] traditional drench application,” he says. However, rates can vary depending on the grower’s objectives.

Using a micro drench strategy, growers will see a toned, uniform plant throughout the entire production cycle, Brotherton says. Requiring less total PGR than regular drench applications, micro drench applications also allow for more flexibility in meeting customer demand, as well as more room for error. And compared to late spray applications, the risk of impacting flowering is reduced.

Micro drench applications of Topflor have produced desirable results on a wide variety of species such as petunias, impatiens and poinsettias, Brotherton says.

When making PGR applications, growers should take factors such as temperature and light levels into consideration, Miller says. “They should always be sure about the environment, and they should know what the temperatures are,” he says. “They should keep track of that kind of information.”

Growers should also keep untreated plants to compare to ones on which they have applied PGRs, Miller says. If the untreated plants aren’t taller than the ones that they sprayed or drenched, they might have made a calculation error or have a non-responsive cultivar. “We don’t have to have growers turn their greenhouses into research facilities, but it bears keeping pretty close attention to this stuff,” he says.

Micro drenching is not a new concept, but many U.S. growers have not yet adopted the practice, Brotherton says. “Growers are always looking to improve their practices to provide a higher quality product,” he says. “With some of the benefits micro drenches provide, I can see a fit for this practice in our industry.”

Results in the field

Morning Star Greenhouses in Spring, Texas, is primarily an annuals and perennials color grower. Marcus Longbotham, general manager and head grower, has been using PGRs for about 10 years.

Longbotham doesn’t micro drench, but he has seen results using a PGR dipping method. “We have to use a really low rate,” he says. “Sometimes we’re talking a quarter of a ppm for some chemicals.” Dips are less labor-intensive than a regular drench, and Longbotham is able to cover more plants with fewer chemicals.

He uses SePRO’s Topflor PGR for both dips and regular drenches, the latter of which usually takes the form of an application between 3 and 4 ppm. Many of Longbotham’s perennials, such as verbena, lantana, lysimachia and Mexican heather, receive Topflor. The plants he dips include Salvia texana, cosmos Sonata series, marigold and angelonia.

Herb Benton is the head grower at Perennials Plus in Westfield, Ind., which grows annuals, perennials, tropicals, holiday pot crops, mums and more. The property has approximately five acres under cover. Benton has been using PGRs for about 30 years, the last 10 of which he has worked at Perennials Plus. He applies them on hostas and echinaceas. Following application, the coneflowers have improved bulking and flower power.

One of Benton’s go-to PGRs is Topflor. “I think, by definition, whatever I do with Topflor would almost fall into a micro drench type of category,” Benton says. On sensitive varieties of calibrachoa, Benton generally applies a 1.5- to 2-ppm split application of Topflor, then makes the same application two weeks later and slowly eases into subsequent applications. On more standard varieties of calibrachoa, in situations when he’s pressed for time, Benton will take the plants off the potting line and immediately water in 4 to 5 ppm.

Benton has had luck with both Topflor and A-Rest on pansies. “I can normally buy pansies that haven’t sold out by April 1, which is when I like to have them out, "Benton says. "I can still keep them looking perfectly good and in bloom with just a couple applications of Topflor and have no problem whatsoever." With A-Rest, he applies weekly applications to tone the pansies.

The poinsettias at Perennials Plus consistently receive a micro drench, Benton says. “It seems like it was down there at the 3 to 7 [ppm] repeated application micro drench,” he says. “And that has worked wonderfully for me, as well. I don’t get the delay in flowering. And I think that is one big benefit that really has to be touted for flurprimidol — Topflor.”

Always read and follow label directions. Topflor is a registered trademark of SePRO Corporation. B-Nine is a registered trademark of Chemtura Corporation.