We talked with Aaron Hathaway, technical services manager for Nufarm, and Josh Weaver, Ph.D., director of research and horticulture at Greene County Fertilizer Co., about plant growth regulators (PGRs) and how they can be a boon for lawn care businesses.

Q: How can plant growth regulators (PGRs) be used to manage tree and shrub growth?

AH: Most PGRs used on trees and shrubs are gibberellic acid (GA) inhibitors, which is a hormone that causes cell elongation. This inhibition doesn’t stop growth altogether, but it helps limit the elongation of cells, which can result in energy that would have been spent in that cell elongation to be used elsewhere in the plant. This energy can be partitioned to more lateral growth and also to increased rooting, especially fine root growth. More fine roots increase the overall plant health and help trees, shrubs and other plants in stressful situations like drought. PGRs can also simply reduce the need for constant pruning, doing much of the work throughout a growing season on its own. This reduction in cell elongation also leads to increased chlorophyll content in leaves simply because the growth has been compacted, which can lead to greener color and healthier plants.

JW: The most serious problem with trees is controlling their growth into utility lines. The idea with PGRs is not to stop growth, but rather to reduce it so the tree can renew itself and achieve a reasonably normal appearance. Some advantages include reducing sprout growth. This will extend the trimming cycle, which will lead to less maintenance expenses.

Q: What should lawn care operators keep in mind when using PGRs?

AH: Not all PGRs are the same. Some PGRs, like paclobutrazol, are absorbed by the roots of plants and therefore, must be applied as a drench around the base of the tree or shrub or watered in if applied to turfgrass. Other PGRs, like prohexadione-Ca, are absorbed by plant foliage and applied as foliar sprays.

JW: Since PGR applications are mostly broadcast applications as opposed to spot treatments, calibration of the application equipment and the applicator is important. Lawn care operators should select properties that will provide the best return on investment: properties with higher labor requirements and large treatment areas that will allow the highest reallocation of personnel.

Q: What are the benefits of using PGRs on lawns?

AH: PGR use in lawns makes a lot of sense, especially in the spring growth flush because we are constantly mowing off top growth and simply discarding it. A PGR application timed in the spring can limit that top growth and help to distribute energy spent on something that would be trashed elsewhere, like roots and more lateral growth. Not only is top growth reduced, but the redirected energy can work to improve plant health and make the plant ready for the stresses of summer, like heat and drought, while improving its visual quality at the same time.

JW: PGRs can slow the vertical growth of the turfgrass, allowing for fewer mowing visits; less trimming and edging; reallocating labor for other tasks; reducing clippings; and maintaining safety in hard-to-mow areas, such as slopes and obstacles. Also, the turfgrass has a healthier appearance as it will grow more horizontally as opposed to vertically. In addition, every trip to the site has costs: fuel, wear and tear on the vehicles and equipment and, of course, travel time. Work at the job site has costs too. This includes the fixed costs, like labor and supplies, as well as opportunity costs. Every hour your crews are spending on one project is an hour not being spent on another project.

Many companies are finding a place for shrub growth regulators in their maintenance programs by using them to free up labor for other work.

Q: Are PGRs more effective in certain seasons or regions?

AH: PGRs are longer lasting in cooler climates. Trees in northern climates may be affected or somewhat regulated by a paclobutrazol treatment for years, while trees in the deep south will not be affected for as long, maybe even half the time, relatively. These PGRs are metabolized in the plant faster as temperatures increase.