GDD Tool – FAQ – 150 GDD?

We’ve recently launched our Growing Degree Day (GDD) tool – (take a look here) and a sure sign of engagement is questions and I’ve had a few. In this blog I’m going to talk about why I keep talking about 150 GDD as a application window for PrimoMaxx II.

What is a GDD application window?

I’m going to assume that since you’re here you have a basic understanding of how GDD is generated and skip straight to why use 150GDD.

A GDD application window is simply how long a period of time do you leave between PrimoMaxx II applications.

Primo’s longevity is heavily influenced by temperature, the cooler it is – the longer it lasts.

So as we move through the season, different temperatures or to different areas of the country we should vary the application window to get consistant results.

We tend to use a figure of 150 GDD in the UK with a base temp of 6 degrees as a starting point.

Lots of work has been done in the USA on Bentgrass with different Base temperatures. Bill Kreuser of University of Nebraska-Lincoln has done lots of work on this but as far as I can gather the UK GDD research is limited.

What are we trying to achieve?

The point of using the GDD program is to achieve consistent results from your primo. The below graph shows how once Primo has been applied the growth suppression goes through a pattern – turf growth reduces, then begins to creep back to normal and then you go into a potential rebound effect.

When timing our next application we are trying to time the sweet spot between the point of maximum suppression and before we go into a rebound effect.

This is a much wider window than we give credit. So whilst I talk a lot about a 150 GDD figure for applying Primo – in reality GDD is a guide and shouldn’t be too prescriptive.

I’d aim to apply somewhere between 100 – 150 GDD use amount of boxes of clippings (or clipping yields) to help guide you. 100 – 150 GDD is an anecdotal figure based on experience, anyone fancy doing a research project for me to tighten that down a little?

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