September 16th, 2024

Hi All,

First up, sorry for no blog last week but the weather forecast was lovely to get up into Snowdonia and that doesn't happen very often !

The weekend just gone I did a night fishing session on the River Trent as the above image shows. Just below where I was ensconced was a tree with branches sitting low to the water and I had watched a Kingfisher fishing from them. I was just wondering if he might land on my rods, when he did !

I couldn't get a photo because he would have flown off so I just sat motionless and enjoyed watching one of nature's greatest fisherman less than 3ft away from me for 5 minutes or so. A little later as it got dark I watched a Barn Owl hunting across the river and as it got darker still, an Otter hunting across the river. And people ask why I love fishing ? The answer of course is because it immerses me in nature and that is where I am my most comfortable. Occasionally of course, I actually catch something as well 😊

There is a connection here with greenkeeping because as we know large areas of a golf course are a great environment for nature, a species-rich corridor between fields of monocultured crops that lack species diversity and of course we come into contact with nature every day when we do our jobs.

Now in my last blog I was bemoaning the inaccuracy of weather forecasts beyond 2-3 days. In that week we picked up 20mm+ of rain across the southern half of the U.K that wasn't forecast 2 days before to illustrate my point. I did get the forward forecast right though for a cooling in our weather which we experienced last week. I went out last Wednesday night looking for the Northern Lights and there was a grass frost on that and the next night with temperatures just above 0°C. That's cold for early September although it isn't unusual for us to pick up a cold few days this month.

Exchanging emails with a meteorologist about the subject of forecast inaccuracy, his viewpoint was that there are certain periods when the weather is no longer conforming to long-established forecasting models due to he thinks to climate change. Certainly from June to now I think forecasting accuracy has been unusually poor.

I spoke last time about one source of this inaccuracy is our inability to predict the behaviour of 'teardrop' low pressure systems that move very slowly, but unpredictably. The rainfall we got the week before last was one such example. The image above from tropicaltidbits.com shows a 'teardrop low' forming from Thursday 14th September as it detaches itself from a northerly low pressure front. (Can you see why I call them teardrop lows ?)

Over the weekend you may have seen the reports of flooding in Central Europe across Austria, and Poland, it was this teardrop low pressure that was responsible. I downloaded a rain report from a Davis weather station in Vienna, that you can see below ;

So in just over 4 days they received 276mm of rain or 11" in old money. This is why the behaviour of slow-moving, low pressure systems are so important for us to get our forecasting head around. The consequences of these weather systems are chaotic and far-reaching.

General Weather Situation - w/c 16th September

No teardrop low pressure systems in the initial part of the forecast this week as we see high pressure build across the U.K & Ireland to give us an Indian Summer feel to the weather. So fine, warm and settled with plenty of sunshine. The emerging high pressure system will swing the wind around to an easterly / north easterly direction and that means it'll keep a hat on the temperatures limiting us to 18-21°C during the day and I think 8-12°C at night, with the warmer temperatures across the south of England. That easterly / north-easterly wind direction will become a feature of September's remaining weather I think. That forecast seems pretty predictable but as we approach the weekend, we see a potential blot on the weather picture as that very same teardrop low pressure system that I referred to over Austria makes an appearance across France / Bay of Biscay area, where it'll redevelop. Now I don't think we are looking at anything like the same intensity of rain so no need to panic, it'll just add the potential for rainfall at the end of the week and pushing into the weekend for the southern half of the U.K & Ireland. So a nice forecast up until Friday and then we see the potential for showers across the southern half of the U.K, with the fine weather continuing north of the developing Bay of Biscay low pressure system.

At this stage the end of the week / weekend suggest that fine weather will persist but it will carry with it more of an unsettled theme as the low pressure introduces moisture in the form of showers and maybe the odd thunderstorm as well across the southern half of the U.K and I think the south east and south of Ireland. It'll up the humidity as well, more on that later.

Weather Outlook - w/c 23rd September, 2024

Now as you'd probably expect with a Bay of Biscay low pressure system slipping into the weather picture, it makes next week's forecast trickier to predict, but here goes...

So I think Monday next week should be a reasonably dry and settled, but I think it's the calm before the storm (literally). Tuesday sees an Atlantic low pressure system push in across Ireland initially and then the rest of the U.K, though it could miss the far south of the U.K. Along with the rainfall, it bring with it strong south westerly winds as well and introduce a more unsettled theme to the weather. As this low pressure pushes rain across the U.K & Ireland, it'll quickly move eastwards with cooler air following behind for a time on Wednesday before another Atlantic rain front pushes in across the north of Ireland into Scotland over Wednesday / Thursday. Further south, high pressure is predicted to push in across Ireland and the southern half of England on Wednesday, so effectively we have a north-south split from the middle of next week onwards - warm, dry and settled for the southern half of the U.K and unsettled across the north / Scotland and Ireland (though the south of Ireland may benefit from the high pressure system as well). Looking beyond that we see the weather cooling at the end of next week as low pressure pushes in across Ireland and the U.K for the end of the month.

Agronomic Notes

Well a lot has been going on in September from an agronomic perspective.

Firstly, we had a big disease pressure period on the 5th and 6th of September, when overnight temperature and humidity increased and we had extended periods of leaf wetness.

The graphs above from our default Thame, UK location, highlight the peak in overnight temperature and humidity and the extended periods of leaf wetness shown on the middle graph. The leaf wetness is measured on a scale of 0-15, with a reading >8.0 indicating dew forming on the plant leaf.

The period I have highlighted in red between 5th September 20:00pm and 7th September 16:00pm specifically relates to Dollar Spot disease with a combination of ideal conditions for this pathogen. Reading the research papers, this pathogen needs air temperature > 15-16°C, high humidity > 90% and a prolonged period of leaf wetness > 10 hours. All of these boxes were ticked during this period.

Thereafter the air temperature dropped back below the point that allowed pathogen development but by then the damage was done on tees, approaches, fairways and greens.

I mention greens because a good number of facilities will have previously only experienced this pathogen on higher-height-of-cut turf but there is a growing tendency for it to affect lower cutting height turf. Locations in the south and south west have been seeing this for a number of years now but the effect is moving northwards and eastwards. The same is true for Ireland I think with the drier east coast now seeing Dollar Spot ingression. The reason I think is down to the need for extended periods of prolonged leaf wetness and for that you need high humidity. Note - High humidity means the air is holding high levels of moisture and is close to being saturated. In this state, it is much more likely for the dewpoint temperature to fall to close to the air temperature and for dew to form on the plant leaf.

I think one of the trends we are seeing is towards a more humid air environment over the U.K and Ireland (well continental Europe as well) as air temperatures increase with our changing climate. Higher temperatures mean the air has the potential to hold more moisture, for every 1°C increase, the air can hold 7% more moisture.

Now you might be shouting out "Ah, but Mark, this summer was the coolest since 2015 according to the Met Office, I read that here". Yes, this is true, but cooler in the summer means normally more rain and therefore higher humidity. The fact is we don't need a hot summer to cause Dollar Spot, we need the air temperature to be above 15-16°C, coupled with high humidity. As we get these unpredictable low pressure systems (yes it's those teardrop low's again) that impart moisture into high pressure systems, we are seeing the above combination in greater frequency and that is driving turfgrass disease.

Not just Dollar Spot but other diseases like Leaf Spot that affects a good number of sports grounds turf and ryegrass in particular. Of course Dollar Spot is none too fussy when it comes to grass species, happy to attack Perennial ryegrass, Fescue species, Poa annua and Bentgrass alike. Of course there are strong cultivar differences in terms of resistance to this pathogen and these differences will I think become even more important as we go forward. It isn't going to be just a case of overseeding, but choosing your cultivar that shows greater resistance to turfgrass pathogens.

Although the highlighted period shows high pressure for Dollar Spot, the days after were still conducive to Microdochium, Red Thread and the like because the drop in air temperature was still in the 'sweet spot' for these pathogens. Consider that Dollar Spot really doesn't get motoring to 15°C, this is the optimum temperature for Microdochium and its growth starts at air temperatures just above freezing.

Heads Up for the weekend...

Just before I leave this subject I am keeping an eye on the conditions for the end of this week / weekend when we have high pressure in situ but during this time it will become affected by the proximity of a nearby low pressure close to the south of England / Ireland. This might see us experience another disease spike as humidity is set to rise at the end of the week.

Growth recovering....

Last week we experienced some pretty chilly nights with ground frost and that really knocked back growth. The snippet above from a golf club in the south west of England shows how the G.P dropped from > 0.9 on the 8th September to 0.33 on the 12th September a matter of days later. For people who got hit by disease the previous weekend, this lack of growth wasn't welcomed because it knocked any recovery straight on the head. Thankfully as you can see from the G.P figures for the 15th and 16th, the growth is recovering to the point where meaningful recovery can be gained with the correct nutrition and overseeding.

Ok, that's me for this week, hope this blog is enjoyable and informative.

All the best.

Mark Hunt