Navigating the Use of Plant Growth Regulators: Best Practices and Considerations

Understanding Plant Growth Regulators

PGRs are substances that, even in small quantities, can have a profound impact on plant growth. They can stimulate or inhibit growth, or modify it in other ways. The key to their effective use lies in understanding the specific needs and sensitivities of different plant species and varieties. For instance, apricots have a low sensitivity to paclobutrazol, necessitating a higher dosage for effectiveness.

Timing and Application Methods

The timing of PGR application is critical. Applying them too early or too late can negate their benefits. For example, naphthalene acetic acid (NAA) can thin young fruit when used during the early fruiting period, while its application before harvest can prevent premature fruit drop. It's generally best to apply PGRs on sunny, windless days before 10:00 AM, and to avoid application on rainy days.

Concentration and Dosage Forms

Choosing the right concentration is essential, as both low and high concentrations can produce undesired outcomes. For example, 2,4-D can promote growth and parthenocarpy at low concentrations but can be lethal at high concentrations. The form of the PGR—liquid for spraying or powder for soil application—also matters, as does the method of application. Paclobutrazol is typically absorbed through the roots and is best applied to the soil, while daminozide, which is stable in soil and has a long residual life, is more effective as a foliar spray.

Site-Specific Treatments

The treatment site should be chosen based on the specific problem being addressed. For instance, to prevent shattering with 2,4-D, it should be applied to flowers to inhibit the formation of the abscission layer. Conversely, treating leaves with 2,4-D can cause damage. Similarly, to stimulate pineapple flowering with NAA or ethephon, the liquid should be poured into the tubular leaf to directly stimulate inflorescence differentiation, rather than watering the soil or spraying.

Frequency of Use

The number of applications depends on the plant's response. Some plants may require multiple applications with smaller amounts, such as using daminozide 2-3 times every 10 days to control the growth of apple saplings. The dosage should be controlled to the extent that the foliage is wet but not drenched.

Combining Agents

Sometimes, multiple issues need to be addressed simultaneously, which can be done by combining different PGRs. Agents that do not react with each other can be mixed to leverage their strengths and mitigate weaknesses. For example, ethylene can be used to ripen pears early, and to prevent fruit drop, it can be mixed with NAA. However, some agents, like daminozide, should not be mixed with alkaline substances as it can affect their efficacy.

Stability and Storage

Many PGRs are not very stable; for instance, indole acetic acid decomposes in light, and ethychlozate loses effectiveness when exposed to alkalis and acids. Proper storage according to their physical and chemical properties is essential to maintain their efficacy.

Complementary Agricultural Practices

It's important to remember that PGRs are just one aspect of plant growth and development. They are not substitutes for fertilizers, pesticides, or other agricultural measures. For example, when using NAA or IAA to promote rooting in cuttings, maintaining the right humidity and temperature in the seedbed is crucial for success.

In conclusion, the application of PGRs must be approached with care and consideration, taking into account various factors to achieve the desired goals. Proper use of growth regulators is a guarantee of their effectiveness and a boon to agricultural productivity.

For further reading on plant growth regulators and their applications, visit authoritative sources such as the National Pesticide Information Center or the International Plant Growth Substances Association.