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  • Writer's pictureMark Hunt

August 29th, 2023

Hi All,

As I sit by my kitchen table and type this blog, I am getting the evil eye from one of the many, semi-tame Blackbirds that populate my small back garden. He lands on the door handle and peers at me accusingly as soon as he sees me bustling around the kitchen.


I think you'll agree, he has a very persuasive stare.


I feed them on a regular basis and I am pleased to say the garden is host to a number of bird species because I am mostly cat-free. You tend to think of your garden in the daylight hours as a home for plants and wildlife but equally at night it serves a purpose for moths, bats, Hedgehogs (which I feed) and surprisingly, a visiting fox. I have a Spypoint night camera which is triggered by movement and takes a photo. I use it to keep an eye on my Hedgehog population without disturbing them.

It looks like Foxes and Hedgehogs coexist whereas I know to my cost, Badgers and Hedgehogs do not.


It shows how given the right conditions, wildlife will populate even a relatively small space.


On a much larger scale, it serves to remind me what a brilliant resource we have in golf courses as custodians of nature. As we know (but Defra and other legislators don't seem to have grasped this fact), only a small area of a golf course (typically 1-2%) is intensively-managed from a nutrition and pesticide perspective. In addition, because our objective is (hopefully) to maintain plant cover 365-24/7, we have a brilliant natural filtering system in place (grass that is) to keep nutrients and pesticides where they are intended to be and not in the water courses. There is plenty of leachate research to show that pesticide and nutrient loss from a well-managed turfgrass rootzone is minimal. Away from these areas in uncut rough and woodland, we have the opportunity to encourage more biodiversity than agriculture could only dream of.


I still think we have more of a PR job to do in this respect although the penny is definitely dropping with organisations like the RSPB and Butterfly Conservation identifying the above potential.


The cooler, wetter summer has definitely benefitted nature with (I think) insects in particular present in greater numbers. Butterflies for sure and this in turn feeds more birds, more Bats and the like. Hotter, drier summers are a big threat to this dynamic and I am so glad we dodged a bullet this time, even if my campervan holidays have been punctuated by windy, wet and not typical summer weather !


I say dodged a bullet because it is around the end of August, you really start to notice the shortening days. At the height of summer (June 21st) we get 16hrs 38 mins of daylength in London for example. Today, in the last week of meteorological summer, we are running at 13hrs 46 mins daylength and by the end of September, we will have lost 2 hours more daylength.


What this means for turf is quite complicated. It relates to dew formation and ET - the process by which moisture is lost from the soil surface and grass plant leaf. The shorter the day, the shorter the time period when ET levels can reach optimum, so we tend to see less moisture loss, which means lower levels of plant stress. The flipside of this coin is that we start to see longer nights and therefore longer periods of dew formation. Of course this equates to plant leaf wetness and it is this factor that ramps up disease pressure from Microdochium (in particular) but also Dollar Spot. I will talk about this later.


So last week, the long term (14 days) GFS forecast had a potentially large storm system forming. Is it still on track or has the scenario changed ?


General Weather Situation - w/c 29th August


As you can see from the animated GIF's above courtesy of tropicaltidbits.com, we start this week with the trough pattern in the jet stream firmly in place, so that means a continuation of cooler, unsettled conditions for this week. Now then, there has been a change in the weather prognosis beyond that with a lifting of the jet stream northwards and this means a cessation (maybe a temporary one) in this seemingly never-ending run of weekend low pressure systems (I make it 7 weekends in a row when we have had rain). More on this in the weather outlook.


So back to this week and we have low pressure departing and another one slotting into the trough. In other words a continuation of the cooler and unsettled weather. Putting some detail on it, Tuesday looks a mainly dry day with some showers across western-facing coasts of the U.K & Ireland and Scotland in particular. Looking on the Netweather.tv v8 rain radar, I can see a band crossing Wales and another band across north west England / Scotland heading eastwards. Usual sort of 2023 summer temperatures 17-21°C, dependent on the location and reasonably light south westerly / westerly winds. The main rain event arrives on Wednesday into the south west of Ireland and pushes across country during the course of the day. Away from this rain front, Wednesday looks a reasonably dry day for the U.K with just some showers pushing into western Wales and The South West in the evening and maybe a few inland.


Overnight into Thursday sees that rain front crossing The Irish Sea and affecting the west coast of England and Wales first thing before tracking eastwards into The Home Counties and Midlands during the course of Thursday morning, clearing Ireland as it does so. There will also be rain across The North West and south west of Scotland. The heaviest rain will be along the southern half of England and it'll be slow-moving, pushing into East Anglia later in the day for some much-needed rainfall I think. Ireland should have a dry start to Thursday but showers will build across the day and perpetuate the afternoon into the evening. Similar temperatures and light winds to the start of the week but the wind direction will be more variable dependent on your proximity to the low pressure.


Closing out the week on Friday, we have another 'pick and mix' weather day with some rain, potentially heavy across The North East and then a raft of coastal showers for the east coast of Ireland / west coast of England, Wales and Scotland. Some of these showers may intrude inland during the course of the day and potentially thundery in nature. High teens looks to be the order of the day with light winds.


Now for the coming weekend, we were due to be on the receiving end of a stormy Atlantic low pressure system according the GFS weather forecast last Monday. Again highlighting the uncertainty in forecasting beyond 7-10 days, we now have a very different outlook.


Quite possibly it now looks to be the first weekend for a good while when we will be largely dry, yes that's largely dry, as a ridge of high pressure puts itself between the U.K & Ireland and Atlantic low pressure systems. Hurrah, about time. This means a nice weekend is potentially on the cards, calm, settled and warmer, with temperatures pushing into the high teens, low twenties. 'Nice' (said in a Fast Show type voice)


Weather Outlook - w/c 4th September


So is this ridge of high pressure a temporary phenomenon or does it set a pattern for the first part of September ?


Well to be honest, I hope the latter as I am off to the beautiful Llyn peninsular in North Wales to overdose on Barra Brith, Flat Whites, some lovely countryside and maybe chase some Bass with the fly rod.


Above is the projected GFS GIF for next Monday and as you can see we have a ridge of high pressure over the U.K & Ireland. To the north west, you can just make out the bottom of the Atlantic storm that was heading our way and below the south coast of England, sitting over Portugal and Spain, you can see a low pressure system. A 'BOB' as I call it (Bay of Biscay low pressure system). Now as we go through next week, there is the potential for this BOB to push northwards and bring rain (and easterly winds) to the southern half of the U.K, whilst the rest of the U.K and Ireland picks up a developing high pressure system. This means drier, warmer and more settled weather away from the south of England through next week. The centre of the high will be north of Scotland which means they could potentially see the hottest weather later next week. So maybe a dry warm week, away from the south of the U.K, that could be affected by the developing BOB low pressure.


Looking beyond the end of next week is sort of Mystic Meg territory but for what its worth, the current weather dynamic is for the high pressure to break down through the course of the weekend after next and for unsettled conditions to build from the south. Now I'd add a bid caveat here, as BOB low pressure systems have a high potential to behave in a contrary way, so I wouldn't attach too much certainty to this feature.


Time will tell.


Agronomic Notes


This week I want to talk about September as a month because I view it as a change month from a plant nutrition and disease management perspective.


The science behind dew formation


At the beginning of this blog, I mentioned the significant change in day and night length that we start to notice from the end of August onwards. The increasing periods of night length allow the air temperature to drop further and further. During this period of time, the air temperature can approach the point where water vapour in the atmosphere condenses to form dew. This is known as the dewpoint temperature, the temperature below which dew forms. You often see it reported on weather forecasts and weather stations alike. Dew will only form if there is enough moisture in the air or put more exactly, if the relative humidity is high enough. So you can have a situation when the air temperature is below the dewpoint temperature but no dew forms because the air is dry / humidity is too low. That is to say the moisture content of the atmosphere is too low for it to condense into water droplets.


Incidentally, the dew image above was taken in the middle of December at midday. The dew had been removed earlier in the day as one would expect but had reformed due to guttation and dew formation.


The 2 metre debate


Now things aren't as clear cut as they seem when it comes to dew formation on turf because of the not inconsiderable part played by climatic variation vs. height above the ground. So for example, a weather station should be located / sited around 1.5-2.0 metres above the ground if it is to generate turf-specific information that is relevant.


Although sticking them on a building makes sense from a security perspective (not that they tend to go walkies due to their size and functionality), I am afraid the data generated is pretty irrelevant because it overstates ET and can in turn provide inaccurate humidity and temperature data due to height, the interference from the building itself and possible thermal complications. (building components can heat up and thermally influence the weather station itself)

A weather forecast assumes ground temperature to be between 1.25 - 2 metre height but wind speeds are often measured at 10m height for example. We of course are maintaining grass at considerably lower heights of cut than 2 metres 😉 and the dynamic is not the same climatically.

To illustrate this point, I have graphed out below the air temperature, dewpoint temperature, humidity and leaf moisture content (as measured using a leaf moisture sensor fitted to a Davis weather station) from a night over the weekend. The sensor has a scale from 0 to 15, where 0 = dry and 15 - totally saturated.

So what we can see is that as the sun begins to set on the evening of the 26th August, the difference between the air temperature and dew point temperature begins to close and (vertical blue columns), moisture begins to form on the leaf moisture sensor as dew. By 20:30, the sensor is saturated reflecting a heavy dew and remains in this state until 08:00 the following day when the air temperature begins to rise and the difference between this and the dew point temperatures begins to increase. By 09:00, the sensor reading is zero indicating that the dew has evaporated with the increasing ET levels.


The key point here is that at no point did the air temperature @ 2m fall below the dew point temperature @ 2m, but yet dew formed at ground level. This is because the air temperature, humidity, dewpoint dynamic is different at turf height than at 2m.


So what we know is that the rule of dew formation at 2m does not apply to a managed turf situation at ground cutting height. I could go into more detail here because I studied this specific climatic dynamic for over 5 years but it wouldn't be wise for me to do so🤐


What we can say is that this type of climatic dynamic with the formation of dew on the grass plant leaf lasting nearly 12 hours overnight, is one that occurs more and more frequently as we move into September. Dovetail that with lower daily ET levels (less drying down) as air temperature begins to fall and we can see that the potential for the grass leaf to stay wetter for longer increases as we progress into the autumn.


What does this mean for turfgrass management ?


Well what this means is beyond the practical problems associated with longer periods of dew formation (clipping pick up, earthworm casting, etc), extended periods of plant leaf wetness drive disease formation. Microdochium, Dollar Spot, Leaf Spot and Red Thread, to name a few but in reality, all fungal plant diseases are encouraged by extended periods of plant leaf wetness.


So rather than waiting till October when we can potentially see some of our most damaging turfgrass disease formation, we need to get our house in order from now on.


This doesn't necessarily mean beginning a pesticide program but in my mind dew mitigation and plant hardener, elicitors, etc should become increasingly part of your IPM program from this point on. Now I know applying a surfactant dew control provides a short-lived affect in early autumn because clipping removal / new grass growth rate is higher but if it serves to bridge a peak in pressure and leave your grass sward largely clean, what's not to like ?


OK, that's me for another week.


Next week I am in Pwllheli but I will be taking my laptop with me so there will be a blog of sorts next Monday.


All the best.


Mark Hunt








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