Ask Us About PGRs By Joyce Latimer and Jim Barrett

Q With so many PGRs available, how do I decide which to use — and at what rates — in a height-control program for herbaceous perennials?

A Though there are more products today, the chemistries haven't changed. Start by learning which products have the same chemistry: B-Nine and Dazide are daminozide products; A-Rest and Abide are ancymidol products; Cycocel, Citadel and Chlormequat E-Pro are chlormequat chloride products; Bonzi, Piccolo, Paczol and Downsize are paclobutrazols; and Sumagic and Concise are uniconazoles. Other chemistries include flurprimidol (Topflor) and ethephon (Florel).

If you have little or no experience with PGRs, I recommend starting with the daminozide products or a tank-mix with chlormequat chloride because they are more forgiving of application errors, and many herbaceous perennials are responsive to them. Be aware that daminozide and the aforementioned tank mix generally have short-term effects, and therefore require multiple applications for adequate control. After you have developed a consistent application technique, you can explore the chemistries that require more attention to uniform applications.

But if you already have experience, start with more potent chemistries to reduce your number of applications. A primary key to success in any PGR program is developing a consistent application technique. If you can do that, you can learn to use any PGR on your crops.

Q What can I do to keep Wave petunias under control?

A Wave petunias and other trailing petunias are great in baskets or gardens, but can be difficult to grow. First, try to avoid growing these petunias in small containers or packs. The Wave series of spreading petunias are long-day plants, and plugs should be produced with lighting to induce earlier flower.

In production of Wave petunias, you'll need to use more PGRs than for almost any other crop, and this is where I see many smaller growers get into trouble. They often attempt to use as little PGR as possible, thinking this produces a better plant, which may be true for other crops — but for Wave petunias, you need an effective PGR program, especially early on in production. The first applications should generally be made seven to 14 days after transplanting, which reduces early elongation for a compact center to the plants. Early treatment significantly reduces the amount of PGR needed later in the crop. Depending on growth rates, container size and individual preference, this application could be repeated at seven to 14 days.

Later in the crop, make a relatively strong drench application — use a paclobutrazol, uniconazole or flurprimidol product — to hold the plants at a marketable size and prevent them from becoming overgrown at retail. The optimum rate for the drench will vary greatly at different production temperatures. Some of the best information on specifics for individual varieties and chemical rates can be found on the breeder's Wave production website.

Joyce Latimer and Jim Barrett

Joyce Latimer is professor and extension specialist for greenhouse crops in the Department of Horticulture, Virginia Tech University, Blacksburg, Va. Jim Barrett is professor of floriculture at the University of Florida, Gainesville, Fla., and GPN's consulting editor.

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