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  • Writer's pictureMark Hunt

July 3rd, 2023

Hi All,

Well we made it to feels a bit like that when you look back at the hard month (from a turfgrass maintenance perspective) that was June.

Listening to the media today, June 2023 is in the spotlight as the hottest, warmest (delete where applicable) month (to be confirmed later apparently) with wildlife suffering. Fish kills due to low water levels and oxygen deficiency, particularly in the north east and Scotland were higher than ever and concerns about wildlife abound, together with a note to let your lawn grow longer to help wildlife. (

The last point I'd dispute to the cows come home as good for wildlife. A healthy grass lawn provides a haven for our garden bird species and Hedgehogs. On Friday night, my outside light went on and I suspected one of my neighbours cats was chancing its arm at the Hedgehog food.(Mine is not a 'cat receptive' garden)

I glanced outside and was amazed to see a big Dog Fox standing there. Amazed because though I obviously know foxes come into towns, my garden has three Hedgehog-size highway access points and is surrounded by high fences. He quartered the garden before vanishing into the darkness and presumably scaling a 6ft fence somewhere along the way !

I know as a fly fisherman, water temperatures were hitting 23°C in our reservoirs at the peak of the heat, that's high and considerably earlier in the summer than usual. The only positive is that reservoir levels here in the Midlands are much higher than they were at the same point last year due to the wet spring. (Not the case in the north of England and Scotland though) and they have since fallen to 19-20°C.

Looking back at our GDD data, it won't surprise you to know that June 2023 has come in as the highest GDD June since I started collating data from 2005. I would also vouch the opinion that June 2023 was our highest E.T June as well. I'll look at some figures in more detail next week but already I know some of them were in excess of 125mm. If we take 60% of that as the amount we are choosing to apply as irrigation, then that's 75mm or 762,000L per hectare. Take into account the strong night winds we experienced in June and I'd vouch a lot of that requirement would have been applied badly, coverage-wise.

High temperatures, E.T, rain rate and wind speed....

Another month of excesses, whether that be excess temperature, excess E.T and excessive rainfall rate / amounts that fell in the storms as the weather broke. I am wondering if June 2023 was the windiest as well with that dominating north easterly wind lasting most of the month ?

Managing turf in such a fast-changing climatic environment is for sure a challenge. So if you are sitting reading this and currently on top of the job, then you are worthy of a pat on the back. It's worth noting mind that we have 8 weeks of summer to navigate before the shorter days start dropping E.T and plant stress levels, so don't relax just yet eh.....

So how does the weather look for the weeks ahead ?

General Weather Situation - w/c July 3rd

Well no weather records are likely to be broken this week in terms of heat because we have low pressure in charge. If you look at the source of the wind, it is pulling down from a cool air area over Finland, Norway and Sweden, so cool is the theme of the week. You can also see those isobars are packed tightly together at times, so that means the windy theme will continue, on and off, not from the north east this time, but from the north west. The wind will drop in intensity from Tuesday and then start to swing round to the west and south west. This change in wind direction will usher in some warmer temperatures later in the week.

Low pressure also means rainfall and currently we have some heavy rain moving across Wales, The South West and the north west of England, together with showers across Scotland / Northern Ireland. Later some of those showers are due to head further south east and may disrupt the first day of Wimbledon (Good luck to Neil Stubley and all of his staff with the event this year 👍). As I mentioned above, it'll feel cooler than 'normal' (whatever that is) for the start of July for the first part of this week, with some warmth arriving later in the week.

So we are looking at some cool night temperatures as well, dropping down to single figures for Scotland and the north of England this week and typically 10-12°C at night and 16-20°C during the day, with the lower temperatures across Scotland, the north of Ireland and North Wales. The warmest temperatures will be across the east and south east due to the wind direction.

From a rain perspective, we will see rain across Ireland, Scotland, Wales and the north and north west of England on Monday and Tuesday, with Wednesday and Thursday looking like drier days for the U.K. Some of this rain will push further south earlier in the week. As we get to Thursday morning, with a change in the wind direction from the south west, we will see a rain front push into the south west / west of Ireland. Some of the rain associated with this front will be heavy. This front will be slow-moving so that means high daily rainfall totals for Ireland during Thursday (and Friday) before this rain crosses The Irish Sea into the north west of Scotland. This rain front will effectively be pinned across Ireland into Friday lasting for most of the day as a ridge of high pressure builds over the U.K. Away from this westerly rain, Thursday and Friday will be drier days for the U.K, with temperatures rising into the beginning of the weekend with mid-twenties likely on Friday and Saturday. That rain across Ireland threatens to spill across The Irish Sea into The South West and western-facing coasts of England, Wales and Scotland overnight into Saturday and this suggests a wet day for the western half of the U.K on Saturday. Later on Saturday, this rain will move easterly and could trigger some thunderstorms later in the day over central and eastern areas. That rain front early on Saturday incidentally will extend right from The South West up to the west and north west of Scotland and move easterly intensifying later in the day across eastern coasts. Sunday sees a dry start for everyone but it won't be long before showers kick off along the south and east coast of Ireland and the west coast of the U.K. These showers will then track inland into Wales and the north west of England later in the day. So the better weather is likely across the east on Sunday. Temperatures will drop back from the highs of Friday and Saturday to low twenties across the U.K and high teens for Wales and Scotland.

'Summer rain' as Karl Gutbrod from Meteoblue once told me, is the hardest to forecast and as usual he is right ! s

So expect rainfall amounts to chop and change this week, either way. The best bet as always is to just look at your rain radar, track the rain direction, react accordingly and don't moan about it 😀

Weather Outlook - w/c July 10th

Above is the projection for next Monday and a couple of features jump out at me.

Firstly, that's the first area of extreme heat (purple) that I have seen this year, so that means 40-45°C for some areas of Spain. Seeing this serves as a reminder that is the only the current low-lying position of the jet stream that is keeping us from a repeat of last summer's heat plume and record temperatures.

The second feature is obviously the cooler and unsettled theme looks set to continue into the 2nd week of July with a succession of Atlantic low pressure systems ushering in rain and strong winds at times. Currently the GFS projection is for this unsettled theme to continue until the end of next week when high pressure looks to extend up from the south to settle things down a tad. Mystic megging it, there looks to be more low pressure systems on the way thereafter but I'd be less confident of this sitting here today. If I was a betting man I'd say next Tuesday looks to be the wettest day of next week for Ireland, southern England and Wales, with more of the rain affecting the north / Scotland thereafter.

Agronomic Notes

Now, I haven't got all of the data in yet for June (a bit like the Met Office it seems) but I wanted to just look at how it stacked up for my default location at The Oxfordshire to give us a flavour from a GDD perspective.

Monthly and Yearly Cumulative GDD Totals - The Oxfordshire, Thame

So looking at the GDD total for June for this location (calculated on a 6°C base temperature), June 2023 came in at 340.4 total GDD for the month.

Looking back this eclipsed the previous highest June GDD from 2017, with 2018 and 2013 also featuring prominently at the top of the pile. I mention this because in 2018 and 2013 we had SSW (Sudden Stratospheric Warming Events) earlier in the year, just like we had in 2023,

That's some coincidence, that 3 of the top 4 warmest June's occurred in the same year we had a SSW event post-Christmas (remembering that 2010's occurred pre-Christmas), so maybe there's a pattern. You know something like ;

  • SSW event disrupts the usual west-east dominant jet stream movement

  • Low jet stream speed = Increased likelihood of meander / trough-peak jet stream pattern

  • Meander-/ trough-peak jet stream pattern = higher potential for heat over Africa and Southern Europe to extend northwards at times.

Can't claim credit for this as someone else (thanks Rob) put that theory forward a few months back :)

The Implications of high GDD June.....PGR Longevity

Well, ordinarily we would associate a high GDD figure with high amounts of growth except we also experienced high E.T and low rainfall in June, so growth was moisture-limited for a good part of the month.

One factor we do know that is affected by temperature directly is PGR longevity.

If you recall the research publication "Avoiding the rebound" (you can find it here ), it looked into the longevity of Trinexapac-ethyl (TE) vs. temperature and found that applying every 200GDD (calculated using the American system of 0°C base temperature) avoided the grass plant rebounding from the effects of being under regulation by a PGR. (In this case TE)

Now 200GDD using a 0°C base temperature roughly correlates to 130GDD using a 6°C base temperature. So I charted out the daily GDD and the cumulative total, resetting to 0 every time it reached 130GDD starting on the 1st of June. So this simulates applying TE on the 1st of June and then re-applying whenver we reach 130GDD.

Here's how the graph looks....

Now normally in the heat of the summer we would be re-applying TE on a fortnightly basis and this just about keeps things regulated. Looking at the stats for June however and we can see that the 2nd application made on the 14th of June would only have lasted 10 days before reaching the 130GDD threshold, because of the high temperature and consequently high daily GDD. So if you saw a big flush of growth towards the end of June (and remember we had two spells of rain in mid-month and at the end of the month), it was probably in part due to losing the effect of PGR regulation and also the growth of the grass plant no longer being moisture regulated.

This work obviously applies to Trinexapac-ethyl as a PGR, but we also have Prohexadione-calcium on the market which has a longer GDD application period in the U.S. Studies claim an application interval of 280-350GDD using a 0°C base temperature which roughly equates to 180-230GDD (using a 6°C base temperature). This would equate to 17-21 days using the June 2023 data. (see here for some research data) It is worth noting though that this work was undertaken on a 9mm fairway height of cut (Gott love that fairway cutting height eh ?) with a mixed sward of Poa annua and Agrostis Stolonifera.

Cutting heights and Anthracnose

Speaking of cutting heights and I know it is a divisive issue within the industry but when we are in periods of heat such as we experienced in June, the smart play is to use the roller as often as the mower to maintain fast greens rather than shave them down to within an inch of their life.

It isn't that you can't cut short of course, it is just that it comes with baggage and you (and that vocal minority of members that want faster greens) have to be aware of that. For instance when we look at Anthracnose, there was a clear correlation in Rutgers research between lower cutting heights and increased Anthracnose, with 3.2mm being the threshold value. So if you are regularly cutting lower then you increase the risk of Anthracnose and have to orientate your agronomic program accordingly.

My Dad used to be one of those vocal minority, always claiming that the greens at his local course were too slow. They had an Open Qualifying Event followed by a club championship and the greens were cut lower for this. The result ? Unplayable for the majority of higher handicap members at the club and I remember my Dad moaning as such.

Of course it is a balancing act that you have to observe. Lower cut greens for short periods aren't the end of the world but as we go into the rest of the summer with 2 definitive Anthracnose triggers already logged, getting that balance wrong has consequences and Anthracnose as a surface-damaging disease is one of the worst.

Why ?

Well because it occurs typically in August / September at its height (maybe earlier this year mind) so right in the middle of peak golf and because it is a slow burner in terms of recovery. I have never seen a Superintendent turn surfaces affected by Anthracnose around in anything less than 6-8 weeks period.

So when it comes to cutting height, I guess I sit in the camp of keeping summer N inputs levels sensible but sufficient, surface O.M levels under control, light and frequent topdressings and using the greens roller to add pace so you don't have to shave your greens down to get extra speed. Just my ten cents worth like.

Ok, that's me for another week, next week I'll take a more in-depth look back at June and what by then will no doubt have been pronounced as our 'hottest June ever', probably. It did make me laugh though when I heard that they were using a 'Super Computer' to crunch the stats in order to deduce this...Well it's the 3rd of July now, doesn't it work weekends ? 😀

All the best...

Mark Hunt

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