Unlock and Play – GDD edition

Can Yorkshire deliver any stress? That's the question I usually open with and at last the answer is yes! This week I'll take a look at why GDD (Growing Degree Day) models are still useful during high stress periods if you have that stress under control.

After a pretty dull July the first 2 weeks of August delivered some decent temperatures. Above you can see how we had a prolonged period in the 20C's with the mercury touching 30C at one point. Of course Bingley wasn't alone and the black line shows the temperature on the South Coast where the max temp regularly moves along around 5 to 7 degrees higher.

What impact did this have on the turf? It's clear to see in the above clipping yield chart that the downturn in growth was significant.

This is where managing a trial situation and turf in the real world differ. In a trial we can purposely induce stress and make the most of of it to highlight the differences in management styles. In the real world you're battling to mitigate that stress in every way you can, rather than allowing it to take hold.

Our stress management treatments showed that we can mitigate some of that heat stress by using a biostimulant and Ryder. The turf quality is better and visually much improved. The image below shows how strong the colour difference is during the stressful periods.

In this situation we have allowed the heat stress to manifest itself and this, in itself, provided the growth regulation - although as this is a trial we will keep up the GDD based Primo applications, which in the real world not be advised.

If your turf was this stressed and no longer growing, a growth regulator application is clearly not needed and you would move your management program into a protection / recovery phase.

Turf managers use many tools to mitigate stress in the heat
image credit - Graeme Roberts - Windlesham golf club

This is the skill of the turf manager, and where GDD programs can play a role. A well timed GDD based program can reduce the amount of Primo used and still produce the same standards. Rarely do we move into prolonged periods of heat that suppress growth and it can usually be mitigated by good stress management practices.

There is certainly an optimum range for growth in cool season grasses - soil temperature of between 16 to 24C (with and a lethal threshold point around 42C). Even the extreme days we see in the UK (and we are seeing more of these) the soil temperatures typically only move out of the optimum ranges for a few hours a day.

Soil temperature will vary in practice, depending on many factors, including soil moisture, thatch / organic matter levels and positioning of the playing surface. Good watering practices and good organic matter management will both help keep soil temperatures lower during these periods.

So even though we are seeing more extreme temperatures, GDD models still have a useful role to play helping us time our PGR applications. Particularly on well managed surfaces that are kept in a healthy state during these periods. If the temperatures are warm and turf is healthy Primo Maxx will be effective for shorter periods of time.

If however you are using Primo on unirrigated fairways, as we move into the summer months, which can be dryer and hotter, then GDD isn't so useful. The additional stresses will be doing a pretty good job of reducing growth for you.

GDD is a great tool for guiding you with your Primo Maxx II applications - it is pretty simple though and should be used with caution. If the turf is stressed to the point that it is no longer growing then you need to work that into your decision making process. If the weather is hot and you have the plant in a position to cope with that stress, then the Primo longevity will be shorter.

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