Around 30 years ago I was a junior playing golf at Cairns GC. Along the left side of the 16th hole in the rough was a roped-off area with a couple of signs that mentioned ‘Primo’ which was sprayed in strips between untreated areas. The difference was amazing and as an apprentice greenkeeper I couldn’t believe you could apply a product to rapidly growing turf and it slows the growth – in FNQ of all places. Usually, if you stand in one spot long enough up there the turf tries to mate with your shoelaces given its growth habit.
Primo®250EC was eventually registered in 1995, followed by Primo® Maxx in 2002 and now by the next generation Primo Maxx® II in 2022. When we consider almost 30 years of use in turf situations, and the learnings we are still making today, has the introduction of PGR’s such as Primo Maxx® II been the turf industry’s greatest achievement?
If I think back to the plots at Cairns GC, it was the reduction in vertical growth that really stood out initially. And that’s the first impression that turf managers have when using a PGR like Primo Maxx® II. Inside the plant, a biosynthesis pathway is converting photosynthate (energy produced in part by photosynthesis) into the growth hormone gibberellic acid (GA) – required by plant cells to elongate. When a plant cell elongates, the leaf grows longer. Primo Maxx® II is targeting the final stage of conversion of this pathway, when GA20 converts to the plant available form GA1. By inhibiting this conversion at the final step, vertical growth is minimised.
But what happens when vertical growth is minimised? Does everything just stop? As time went on, the more we learned about the associated benefits of PGR applications. One learning was a reduction in internode length, a tightening of the sward and an improvement in colour.
Imagine a football field that has solar panels placed across the surface and in between each panel is a space to move between each row. The total energy output of the panels would be consistent day to day in full sun but would vary in shade. This is consistent with a turf surface without any PGR applied to it. Now imagine that same field where the space between each panel is removed and the panels are side by side. More panels could fit and as a result, more energy is produced. This is consistent with a turf surface with PGR applied to it. The tightening of internode length means more leaf blades per given area. More leaf blades in a given area means more chlorophyll and an associated improvement in colour. More leaf blades and more chlorophyll means more energy is harnessed through photosynthesis.
As vertical growth is minimized, the energy produced is transferred to other parts of the plant. When excess energy is produced by the plant it stores it in the roots and as a result, root mass is increased. This is one of the major growth responses of turf in full sun compared to shade. In shaded environments, turf stands usually can’t produce the required energy as photosynthesis is reduced. As such, the plant draws on stored energy in the roots and the result is a shortening and thinning of the roots in shaded locations. Shaded locations are where light rates of PGR’s are effective. The increase in chlorophyll content means the plant is able to harness more available light, convert to sugars and help drive enzyme processes.
Root Enhancement with Primo Maxx® II
As root growth and mass increases when PGR’s are applied, nutrient uptake is enhanced – further supporting overall plant health. The roots are able to access improved levels of moisture within the profile and when coupled with less transpiration due to less vertical growth, a reduction in water requirement through irrigation is realized. It was one of the main plant performance outcomes I noticed as a Superintendent by being able to move from around 3 times per week irrigating fairways to 2 times or less in summer. When you consider not just the less water applied, but also less power to run pumps, less strain on the irrigation system – there is a case for considerable savings in water alone particularly as we enter the next El Nino phase.
Primo Maxx® II Plant Health Benefits
More research work has been undertaken as to how to time applications of PGR’s to continue and enhance the plant health benefits through repeat applications. This is known as Growing Degree Days (GDD) with GDD a measure of heat accumulation. Research has shown the optimal value for warm-season turf types treated with Primo Maxx® II to be around 200GDD. Calculators, such as the free version on the www.syngentaturf.com.au website, monitor your minimum and maximum temperatures and then apply a base temperature value to the average – either 10C for warm season grass or 0C for cool season grass, as the temperature above these values initiates growth in each respective group.
By working within a 200GDD value, the plant stays with the suppression phase enabling it to enjoy the health benefits and for you to enjoy less cutting. If however you move beyond the suppression phase and the PGR wears off, then the plant enters the rebound phase where the flush of energy being transferred to other parts of the plant like the roots, is directed back into leaf cell elongation. The result is a significant amount of top growth and an increase in mowing activity again. This can lead to scalping and incursion of weeds and pathogens in these areas as the turf is weakened or if subjected to a sports field situation, a loss of surface durability and performance.
Suppression v Rebound Phase
Now is the time to apply to your turf to realise the health benefits and cost savings that are real. From a PGR programme using Primo Maxx® II, you will:
- Mow less: meaning less labour; less fuel; less R&M.
- Water less: meaning less labour if manual; less power to run pumps; less R&M on the system; and less water if you are paying per unit.
- Have a healthier plant: with enhanced uptake of nutrients; higher relative water content of the leaf improving heat stress management; and higher chlorophyll content for improved health in low light situations.
- Have less overall stress.
The more we have learnt about PGR’s the more benefits are realized and we will continue to learn more as time goes on. So, are PGR’s such as Primo Maxx® II the turf industry’s greatest achievement? For adaptability and benefits across a wide range of turf types in a wide range of growing conditions under a wide range of end usage – I firmly believe they are.
For more information on Primo®250EC and Primo Maxx® II visit www.syngentaturf.com.au.
