Early application of plant growth regulators could have worthwhile benefits for disease control and rooting in wheat crops this spring, according to leading agronomy provider Farmacy.
With crops at a range of growth stages coming out of winter and last season’s high lodging incidence in many areas still fresh in the mind, there may be clear benefits to both forward and more backward crops, says the firm’s David Howard.
Lush, thick crops are often at greater disease risk, especially from Septoria, which is spread by rain splash within the canopy. However, any period of rapid growth can result in soft plant tissue that is more vulnerable to infection, he says.
Growers should try to maintain steady growth throughout the season and avoid sudden surges as many experienced last spring when rain after a prolonged dry spell resulted in a flush of rapid growth, weak stems and lodging in some crops.
“Because it was so dry and crops were stressed, a lot of growers quite rightly, either reduced the dose or did not apply later growth regulators. By the time rains came, growth response was extremely rapid and it was too late to do much about it with PGRs.”
To avoid a repeat, he favours a “little and often” approach to PGRs from T0 onwards to keep growth under control, and promote other benefits, such as improved rooting.
“An early PGR can have a big impact on root stimulation during the foundation phase up to GS30. It’s not just about canopy control. Improving rooting should enable all crops to access more water and nutrients, which means they are healthier, suffer less stress and are not as susceptible to disease.”
It’s an approach favoured by Lincolnshire-based Farmacy agronomist Charles Wright, who says PGRs are generally best applied early at T0 and T1 to build root mass and manipulate canopies, rather than delaying applications and trying to rectify problems later in the season.
Although early-drilled wheat is generally well developed, a lot of later-sown crops are less advanced and some fields show big in-field variations in growth stages, so a tailored approach to PGRs will be essential.
“Variety, soil type, nutrient regime (artificial and organic fertilisers) and weather all influence the exact approach you take, but in general I prefer to go early and use a mixture of different PGR actives rather than relying on a single mode of action.”
Plant growth regulators work by targeting different parts of the plant growth hormone cycle, so using products based on a range of active ingredients will affect different parts of the growth chain and provide more effective growth manipulation than a single active, explains Mr Howard.
Few PGRs are approved for use prior to GS30, but some based on trinexapac-ethyl can be applied. He suggests including these with the first T0 fungicide to manipulate rooting and tillering and follow with a full PGR programme at T1 and T2.
Chlormequat is another option that can be used alone, or included with trinexapac-ethyl if growth is very advanced.
A chlormequat plus trinexapac-ethyl mix is Mr Wright’s preferred approach for the majority of winter wheat, although he points out that warmer conditions and active growth are needed for best results. For early PGR applications when conditions are cooler, products containing prohexadione may be another option to consider.
Dose should be tailored to specific field conditions and variety. “It’s important to have a plan for what you’re trying to achieve with PGRs, but don’t be too prescriptive. Every field must be managed individually,” says Mr Howard.
He also reminds growers of the intrinsic link between canopy structure and nutrition, so PGR and fertiliser programmes must be managed in tandem.
Canopy manipulation
- Thick, lush canopies at greater disease and lodging risk
- Use PGRs to maintain steady growth
- Early PGR use can stimulate rooting – aids water and nutrient capture
- T0 spray is key time to promote rooting and control canopy
- Utilise a range of chemistry for more effective growth manipulation.
