Hi All,

Just a quick update on next week’s weather as it’s looking feisty and some information on a couple of downloads from the blog.

Weather Outlook

A note of caution surrounding next week’s weather. Already we have seem a much colder January than the ‘new normal’ with a number of snow events including today for Scotland and the north of England. Next week there looks to be a high potential for further snowfall and likely further south as well if (and it is an ‘if’) the scenario detailed above pans out as projected in the GFS output. With low pressure to the west, north and east of us at the start of next week, the projection is for these areas of cold air to merge and form a trough event powered from the east and north. At the end of next week low pressure looks to form to the south of the U.K and that’ll pull in easterly winds on its trailing edge. So for me there is an increased likelihood of cold air from mid-week, next week and an increasing risk of snow, first up across the north but potentially further south as well. Now as we know things can and do change from a weather perspective and we are talking 7-10 days out so we are right on the edge of forecasting accuracy but I’d say the potential is clearly there for another ‘Beast from the East’ -type scenario.

Looking beyond this the run of colder air is set to possibly continue right through to the end of January if the north and east trough stays in situ

Not the greatest scenario for us all right now I appreciate but it is what it is, another ripple in the pond (and it’s a choppy pond at the moment all things considered !)


I have had a number of requests for the 2021 GDD spreadsheet and like most things this year it’s been a bit delayed, so please accept my apologies for this.

I have taken on board some suggestions for 2021 in the new spreadsheet and incorporated some extra columns for logging humidity, E.T and Clipping Yield for those of you who have access to this type of data.

In turn I have also used the data to calculate the Smith Kerns Dollar Spot probability prediction so if you are able to input maximum and minimum air temperature along with humidity you’ll see how this shapes up in terms of the probability of Dollar Spot. Now a lot of sites don’t have an issue with Dollar Spot but this equation has shown itself to be a good indicator / predictor of some other turfgrass diseases including Microdochium (in the autumn rather than the winter), Red Thread and I think Leaf Spot on Lolium perenne. Normally the Smith Kerns model doesn’t start till April and in practice temperatures drop to below their formula threshold during October / November (less than 10°C and more than 35°C for the Dollar Spot pathogen), but I’ve put it in all year in the spreadsheet just for you to have a look see. I am grateful to Paul Koch for allowing this usage and I would urge you to have a look at the technical feature on the Smith Kerns Dollar Spot prediction model here

In the U.S they would use a threshold probability of 20% as returned by the model calculation to commence preventative applications of fungicides for the control of Dollar Spot, their worst turfgrass pathogen. Now for us our approach is of course different. I think the main benefit would be to determine for your site when you see pathogen activity from Microdochium, Dollar Spot, Red Thread, Leaf Spot, e.t.c and how that links in with the Smith Kerns Model so you establish your own threshold values. I have been doing this on some sites for the last 2 years and in practice with Dollar Spot here I have seen a reoccurrence of Dollar Spot when the probability exceeds 60% on some sites and 75% on others. Now as mentioned earlier I fully appreciate a lot of sites do not suffer from this pathogen but those that do will know it is a re-occurring one and so this is hopefully useful in the first instance to those end-users. For others it may or may not be useful when looking at the other pathogens I have listed. Either way it’s worth a go I think.


Each month now has two graphs under the data entry page, one showing daily G.P and the other daily rainfall. Both of these can be printed off as a pdf by simply hitting the button on the spreadsheet and may prove useful for communicating to members, management on issues relating to playability, growth, etc. I have picked these two measurements because I think they represent the most often requested information from end-users and management alike ” How much rain have we had this month”, “the greens don’t seem to be recovering very well”….you know the kind of thing by now 🙂

I have added some extra charts on the chart tab to show how the Smiths Kerns model worked through the calendar year and again it will hopefully be useful to marry up this output with what you actually see on the ground.

The 2021 GDD spreadsheet is available to download here 

GDD / G.P Calculations

In this week’s blog I covered GDD and G.P calculations and how they work in practice. First up, I made an error in the G.P calculation on example day 2, the G.P figure should have said 0.55 instead of 0.77. I think my brain was a bit addled from all of that number crunching so I blame this and old age 🙂 I’m very grateful for Peter Jones from P.J Lawn Care for pointing this out to me. So I decided to produce a downloadable pdf which features both the GDD and G.P calculations with some additional worked examples and commentary in case you want to use either of these formulas in the future. You can find it here

Think that about wraps up this week, stay safe and healthy 🙂

All the best.

Mark Hunt