August 2007

Ask Us About PGRs By Joyce Latimer and Jim Barrett

Q Why should I use PGRs on my herbaceous perennials and how do I get started?

A Plant growth regulators (PGRs) can enhance the appearance, quality and salability of your herbaceous perennials just like they do in the color annuals world. If you are a grower who is new to PGRs, start with the softer chemicals like B-Nine or Dazide (daminozides) or the tank mix of B-Nine or Dazide with Cycocel (chlormequat chloride). If you have some experience using PGRs or have a lot of crops that are not responsive to B-Nine or Dazide, then test the more potent PGRs like the triazoles or Topflor. The importance of on-site testing cannot be overemphasized. Differences in application techniques from one nursery to another are exacerbated by the differences between individual applicators and their equipment within the same nursery.

Growers should consider any recommended rate as a starting point for their own trials. Work on developing a consistent application method, preferably applied by a very limited number of people always using the same equipment. For the soil-active PGRs, learn to use volume to give you different application rates so a single solution can be used to treat multiple crops. One of our growers makes a second application to some species during his spray application to effectively double the rate applied to that crop without having to make up a new spray solution. Consider the newer application methods like media sprays or liner dips that may reduce worker exposure and restricted entry interval issues. In addition, they can increase the flexibility of your treatment and planting schedules. Look carefully at using drench applications to reduce impact on flowering. Work on consistent application methods. PGRs increase flexibility for production, marketing, shipping and retailing. Plan to use PGRs as part of your production schedule.

Q How should I adjust my PGR use on poinsettias when I am growing at cool temperatures?

A Learning how to control height is an important part in the process of moving to cooler temperatures with poinsettias. In general, poinsettias grown cool do not need as much growth regulator, but it is never just that simple when PGRs and poinsettias are concerned. Cooler temperatures generally produce smaller bracts. However, the effects of the cooler temperatures are not as dramatic as anticipated because it is compensated for by the fact that there is less reduction due to growth regulators, if size control is done right.

One approach to cool growing that many growers are starting with is to keep the crop at normal, warm temperatures until after flower initiation and then lower the temperatures to a daily average of about 60¡ F. During the warm vegetative period the plants will be growing as fast as they always have. However, you will need to be careful and not put on too much growth regulator during the vegetative period. This is because the plants will slow down quickly when the temperatures are dropped and the PGR that is applied before initiation will have more effect than in previous years when temperatures remained higher. Also, after the temperatures are dropped, any growth regulator used will have a greater effect on both height and bract development.

For cool growing, it is important to understand the effects of shifting varieties and changing schedules. Many growers will change to normally earlier finishing varieties. Some of these are less vigorous and naturally need less chemical height control. Also, if planted on the same schedule as used for midseason varieties, they will have less vegetative growth time since they initiate earlier. On the other hand, some varieties being promoted for cool growing actually have high vigor, which works well if temperatures can be kept down from the beginning. But the vigorous varieties may require more growth regulators where early temperatures are not cool.