Many growers use plant growth regulators. They may use them to improve the aesthetic quality of plants. For example, most Easter lilies are sprayed with A-rest to produce very condensed plants. Shorter Easter lilies are more prized in American than are their taller counterparts. Plant growth regulators are also used to lengthen the shelf life of juvenile plants. Wholesale growers often spray their plug tray plants with plant growth regulators to prevent them from becoming overgrown in a short period of time. Growers may use plant growth regulators to decrease shipping costs. By keeping their plants small, growers can fit a larger quantity into each truckload. Plant growth regulators are very widely used, which makes them an important topic of knowledge. There are many plant growth regulators available and I will describe the most common ones in this paper.

A-Rest, B-Nine, Bonzi, Cycocel and Sumagic are plant growth regulators that act by inhibiting the plants production of gibberellins. Gibberellins is the plant hormone responsible for internode elongation. The inhibition of this hormone results in more compact plants with smaller leaves, darker green leaves or both. In certain cases, the flowers of treated plants are smaller and flowering may also be delayed. These chemicals do not cause flower abortion so they can be used at the end of production.

A-Rest is very safe and easy to use. A-Rest is very active on most crops except geraniums and impatiens. It is commonly used in the plug production of pansy, vinca and other plugs that are sensitive to Bonzi and Sumagic but uncontrolled with B-Nine or Cycocel.

B-Nine and Cycocel are effective on most crops and are the easiest to use. Both chemicals have only moderate activity so multiple sprays are needed. But the moderate activity of the two chemicals greatly reduces the risk of severe plant stunting. These chemicals work best in cool climates.

Bonzi and Sumagic are active on all crops and are more effective than B-Nine or Cycocel. Usually only one or two applications of these chemicals are required. These chemicals are active even in very warm climates. Due to their high level of activity there is an increased risk of excessive stunting due to over application. These two chemicals must coat the plant stems and absorb into the growing media to be active, they are not active when absorbed through plant leaves. Begonias, pansys and geraniums are very sensitive to Bonzi and Sumagic, petunias and marigolds are less sensitive.

There are several options when choosing a plant growth regulator for your crop. Remember, before applying any plant growth regulator to your entire crop do a trial spray on a small group of plants to ensure the chemical will give you desirable results.

References

GPN greenhouse product news. Nov, 1999. Volume 9. Number 11.