Ask Us About PGRs

August 7, 2009 - 10:37

Q Which PGRs should I use on summer-planted perennials for sales the following spring?

A For summer-planted crops, your goal this first growing season is to bulk up the crop and maximize root growth. However, the bulking up is often very rapid, and you end up spending a lot of money in time and labor pruning the crop. So take advantage of plant growth retardants to slow down the shoot growth of the vigorous crops. Select the PGR you are most comfortable using that is also effective on your crop. (See the PGR database at www.gpnmag.com for help on selecting effective PGRs for your specific crops.) Some growers prefer to begin a growth retardant regime after the first pruning. Then they know the pot is filled out.

For crops that are slow to fill the pot, consider using the branching agent Configure (6-BA). We are still testing this product — applied as a foliar spray at 600 ppm — on a wide variety of perennials. We are finding essentially no phytotoxicity on any of the crops, and Configure has improved branching in the majority of the crops that we have treated. The most valuable increase in branching for the grower is the increase in basal branching of crown-type plants like echinacea and heuchera, but we are also seeing increased lateral branching on the shoots of crops like phlox and gaura. We have not seen many crops with an increase in the number of shoots in the pot. We recognize that these branched shoots may not overwinter for spring sales, but the increased shoot mass this summer will enhance root growth to provide a better plant for spring. And for tall crops that need encouragement to branch, you can also use the growth retardants and Configure. I would not suggest tank mixing, but we have found no reduction in the growth control or branching effects of plants treated with both compounds during production. And if you see increased branching on these crops this summer, remember to treat the plants with Configure again in the spring to improve pot fill.

Q What is the best PGR to use on fall pansies?

A Fall pansies are different from spring pansies: There is a fine line between too little control and too much. First, try to grow them outside or under the highest light conditions possible. Avoid a hot, low light structure. Tank mixture sprays of daminozide and chlormequat are the softest approach for less vigorous varieties and where temperatures are cool. But this often does not give adequate control or last long enough. Stronger options are ancymidol, flurprimidol (Topflor), paclobutrazol and uniconazole. The best option really depends on individual situations. Ancymidol is probably the one “better” chemicals for pansies. Its cost is a little high, so most growers only use it on plugs. Many growers use paclobutrazol because they are familiar with it from its use on so many other crops. But I don’t think it should be the first option because its activity on pansies varies from time to time and with different varieties. It is difficult to obtain uniform response with paclobutrazol when you want a medium level of control. If you are familiar with uniconazole, it is a more predictable option than paclobutrazol on pansies. But paclobutrazol and uniconazole can both cause too much stunting and delayed flowering if the rate is too high. With paclobutrazol and uniconazole, drench applications made after the plants are well established are better than sprays and should be used more widely on pansies. Topflor is newer, and its use on pansies will likely expand as we gain more experience with it. It is not uncommon to make a strong PGR application late on fall pansies to hold them until they are shipped. While this works for the grower, it is not a good product for the consumer as these plants perform poorly in the garden.

About The Author

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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