PGRs (Plant growth regulators): Harnessing PGRs to enhance yield and quality

Meeting the needs of the 2024/5 season

With the difficult autumn resulting in numerous different scenarios in the field in terms of crop potential, there is a common link that connects them all – the need to protect yield.

In a year where we are likely to see a reduction in overall production based on cropping areas, it’s essential to optimise the potential of these crops and protect this potential throughout the growing season.

The use of plant growth regulators (PGRs) has become more commonplace in many arable rotations, with growers and agronomists regarding them to be an essential agronomy tool for the management of modern, high yielding varieties.

This increase in popularity can be explained by two key factors:

1. The increasing frequency of volatile and extreme weather has made it increasingly difficult to manage high yielding, top-quality crops. PGRs are therefore used to mitigate the effects of periods of intense drought which can limit moisture and nutrient availability, and/or the constant threat of wet and windy conditions which can exacerbate the risk of lodging.
2. Improvements in plant breeding programmes, the increasing popularity of biostimulants and a closer focus on nutrient use efficiency, all have the potential to produce healthier and taller crops. PGRs are therefore used to reduce the threat of lodging and are considered of critical importance where a naturally taller or weaker variety is being grown, on highly fertile land or soils which have received high levels of nitrogen, on light land or poorly consolidated seedbeds, and where disease such as eyespot threaten to weaken the plant.

How PGRs work

Two hormones (auxins and gibberellins) are responsible for controlling plant growth and development in cereals.

PGRs are commonly used as a cost-effective way of limiting cereal stem extension, but PGR programmes must target both hormones to work effectively.

Three of the key PGR active ingredients that are registered in the UK include:

1. Chlormequat chloride (CCC)

• Inhibits plant growth by interfering with the biosynthesis of gibberellins
• Shortens and thickens the plant stem – an important opportunity to take in early spring to engineer some strength into these crops before they bolt when the weather turns
• Increases rooting and tiller development

2. Trinexepac-ethyl (TXP)

• Inhibits plant growth by interfering with an enzyme responsible for the biosynthesis of gibberellic acid
• Shortens and thickens the plant stem
• Increases rooting and tiller development – especially important in a year where crops have not had to work hard to find water up-to-now, but as we have so often seen, it can dry up and not rain for months, so rooting development is another key opportunity to take in early spring
• More efficient gram for gram than CCC and at lower temperatures

3. Ethephon (ETH)

• A strong auxin inhibitor: taken up via leaves where it is converted to ethylene which limits cell elongation and, instead, increases cell width
• Ethylene also reduces apical dominance, therefore increasing auxiliary branching to create a larger canopy. However, if used close to flowering can cause abortion or delayed flowering
• With the area of spring barley predicted to increase considerably following a reduction in winter wheat planting this autumn, Ethephon is a very important option for reducing brackling