September 14th

Hi All,

Back from my Covid-19 limited travels after spending some enjoyable time exploring North Wales, an area I was previously quite unfamiliar with save for a crazy idea once to mountain bike with panniers from Builth Wells to Machynlleth and back one October over the course of 3 – 4 days !!!

The Bass eluded my fly, a big Welsh Trout didn’t and the weather played ball some of the time. One morning I opened the curtains and I was faced with clouds to the ground drizzle and the temperature sitting in the low teens during most of the day. Looking at my weather station data across The Midlands, South and East of England, I saw temperatures in the low twenties and E.T building. It struck me how diverse an island we occupy and reminded me how one persons wet day is another’s continuing drought, the same is true for that other island across The Irish Sea with big weather variability, west to east, north -south.

Difficult then for me to sum all of this up in a weather blog so again I’d ask your patience when it comes to the subject areas I concentrate on, some will be relevant weather-wise, some won’t, but hopefully they’ll continue to be informative until the day beckons when I hang up the pen / keypad on a Monday morning 🙂

Back out walking in familiar countryside I noted how some fields of late-sown winter wheat and spring Barley were only just being harvested now, fields that caught the wet spell at the end of August that delayed many a harvest. The Welland valley had a cloak of dust over it as farmers hurriedly ploughed their fields in an effort to get their next crop in. Maybe it was just me but  I noted an air of urgency about proceedings, maybe they were mindful that at this point last year, we were only 10 days away from the date when a dry September transformed into the beginning of a 5 month wet spell with little or no drying days.

Difficult to imagine at the moment when we have had less than 1.5 mm here this month so far, but September 2019 followed the same pattern until the 23rd of the month….

So let’s look at how the weather is shaping up over the next 10 days or so….

General Weather Situation

Looking at the GFS output above for Monday the 14th of September, we can see we have a ‘high’ jet stream position with a big plume of warm air extending up from Africa to the U.K and Ireland. As you’re probably aware by now we are set for a mini-heatwave this week with heat building through Monday and Tuesday and then slowly subsiding through the week to normality at the weekend. As it often happens with this type of weather pattern, the cooler, wetter weather gets pushed north and that’s why Scotland and Northern Ireland picked up some heavy rain recently.

Onto this week and a stable affair during Monday and Tuesday with the heat building slowly after a pretty cool, single figure start to the day. With light winds expect temperatures to pick up to the high twenties for England and Wales on Monday and Tuesday. Ireland will be something of a west-east divide as will Scotland with an Atlantic low pressure feeding in rain to the west of Ireland through Monday afternoon / evening. This rain will track northwards into Scotland overnight with the west of Scotland and central areas ‘enjoying’ a wet Tuesday. The east may just miss the worst of it though. As the heat builds further south on Tuesday it may just trigger some thunderstorms across the south of England. Despite the threat of rain, Ireland and Scotland will have high teen / low twenties temperatures peaking on Tuesday and that means more Microdochium nivale pressure and more worm casting for these areas 🙁

As we move into Wednesday, the high pressure pushes up north and east and that means a change in the wind direction to north easterlies. This will do two things to our weather, firstly it’ll push more cloud into the Scotland and the north of England / north Midlands and secondly it’ll drop the temperatures down to the low – mid twenties for England and Wales, declining further as we move through the week.  A dry picture then for all of the U.K and most of Ireland (save for the odd shower across The Irish Midlands on Wednesday) through Wednesday and Thursday with pleasant temperatures and variable amounts of cloud. The wind will remain north easterly / easterly and that’ll push more cloud into eastern and central areas of England on Thursday. As we close out the week on Friday we see the odd showers across north west Scotland, but still remaining dry for Ireland, England and Wales with plenty of sunshine after that cloud cover has burnt off. Temperature-wise, high teens for Ireland and Scotland, but low to mid-twenties for England and Wales.

Going into the weekend we have a Bay of Biscay low pressure trying to enter the weather scene and this will push in cloud and the possibility of rain to the south coast of England through Saturday and Sunday though a lot is dependent on exactly how that low pressure behaves position-wise. Away from this possible incursion of moisture we look set for a dry weekend on the whole for most of England, Wales, Ireland and Scotland though the threat of showers moving up from the south may increase through Sunday for England and Wales. With a low south of us and high above us, the wind can only be from the east and it’ll be moderate to breezy at times. This will hold back the temperatures to the high teens / low twenties for all of us with more in the way of cloud building on Sunday.

Weather Outlook

A very different looking GFS output for the start of next week compared to this one with that southerly-orientated low pressure system set to bring a cooler start to next week than this. That said I don’t think high pressure is quite finished with us just yet. In fact as it looks now, September 2020 may indeed turn out to be one of the driest on record for England anyway dependent on who wins next week’s battle between low and high pressure. As it stands now, next week looks to start off dry and settled with pleasant rather than warm temperatures, I’d say high teens to low twenties would be about right. That low pressure system and the prevailing easterly wind direction may create and drag some showers in off The North Sea through Monday and Tuesday but on the whole these look to be few and far between.

As we approach Wednesday, an Atlantic low pressure system pushes rain into the west of Ireland and north west of Scotland. Some of this rain will push inland but at this stage it looks more north and westerly-orientated. A more consolidated weather front is projected for next Thursday with heavier rain for Ireland and the north west of Scotland.  This rain will move into Wales and northern England overnight into Friday crossing the U.K, again tricky to say who will get how much when but I don’t think we will see that much for central and southern England. As we approach the end of next week / weekend we see high pressure build and that will push any rain more west and north and set us into a fair end to September.

So at this stage I can’t see a repeat of late September 2019 when the weather changed on the 23rd September, the jet stream dropped and the rest is history. Looking at the GFS projections from both ECMWF and GFS, the jet stream looks to be sitting in a northerly position which means continental high pressure will fill below it and push the majority of the rain north and west. Maybe a late raid to North Wales for Bass could still be on the cards…

Agronomic Notes

A bit of a catch up…..August and September have been a bit of a rodeo ride from a temperature, rainfall and growth perspective and this has had some quite clear consequences in terms of turf management.


Looking back at August we see the effect the heat had on growth between the 6th and 13th of the month with a pronounced dip in Growth Potential (G.P). This dip was once of the strongest that I have recorded at this location since I started using Growth Potential.

As we have discussed before one of the strong points of using G.P as a predictor of growth vs. GDD is the ability for the Growth Potential formulae to take account of a potential reduction in growth due to plant stress with a standard optimum temperature of 20°C for cool-season grasses. I use 18°C in my model because I think this more accurately reflects the effect of high temperature growth reduction on Poa annua-dominated swards.  Once we reached the middle of August, we got a double whammy, a swift reduction in temperature and the arrival of rainfall.

This resulted in a massive growth flush and I remember it being the week when I forecast “The greens are slow, the fairways haven’t been cut and the bunkers are washed out” feedback potential from hermetically-sealed golfers. What was interesting was what happened in the last week of August. Some superintendents reported that the growth flush continued unabated, others that the greens dropped off completely with little or no growth despite reasonably good growth conditions. Some of this drop-off in growth was due to some pretty cool nights with ground frost reported by some but some of it I think was down to the grass plant and a potential exhausting of carbohydrate reserves.

During the heat we know that the grass plant shut down and photosynthetically was way below optimum, so it is likely in my mind that the plant was at a low level from a carbohydrate reserves perspective. Come the arrival of rain and cooler temperatures, the speed and magnitude of the growth flush in some cases I think exhausted the carbohydrate reserves of the grass plant before it had a chance to produce more. Dove-tailed in with that potential drop in reserves was a drop off in Solar Radiation towards the end of August (cloudy and dull weather) so the grass plant wasn’t able to photosynthesise at optimum levels.

Below is a graph of the Solar Radiation for the same time period, you can clearly see the drop off at the end of August.

So we experienced a bit of a rodeo ride in terms of growth, not everyone mind, some reported high levels of clippings continuing unabated through this period, but others said the greens dropped off markedly.

To summarise, I think the reason was a lack of carbohydrate reserves due to the hot spell, depletion during the following growth flush and then sub-optimal temperature and light levels at the end of the month. You can see things in September have settled down somewhat with some consistently high G.P figures. In my mind though just chucking fertiliser on to try and re-stimulate growth was not the right call. Apart from trying to push a grass plant that was operating at a below-optimum carbohydrate reserves perspective, the lack of light would probably have just caused more upright, etiolated growth with thinner cells walls (easier to invade from a disease perspective) and a less tillering / thickening growth habit.

Disease activity

With the arrival of rainfall after the heat came humidity, some mild night temperatures between 15-20°C and this kicked off most of the usual suspect turfgrass diseases. Anthracnose flared up on Poa-dominated greens, Microdochium nivale also and we saw huge amounts of Red Thread on Fescue / Ryegrass swards. In addition the heavy dews experienced during this period encouraged Dollar Spot to make an appearance both in the U.K and also Ireland. I have outlined the specific period of sustained high humidity and temperature on the chart above but no doubt in my mind it led to high levels of Microdochium in turfgrass stands from the 3rd week of August onwards. Although we haven’t repeated the duration of high humidity we have seen continual peaks of mild night temperatures and high humidity since and this has led to ‘flare ups’ through September despite it being a dry month for many. (Midlands south in the U.K mind)

Now one of the consolations of early disease outbreaks is that they tend to grow out very quickly and if you have a mind to overseed a more tolerant grass mix into the affected areas, the soil temperature is high enough to generate quick germination and therefore recovery. Certainly you’d hope that we would be able to manage this amount of disease without having to resort to the dwindling choice of fungicides still available on the Chemsafe shelf. As we move out of September into October that situation usually continues from a potential recovery perspective however the damage potential from Microdochium tends to ramp up.

Diseases like Red Thread, Microdochium nivale and Dollar Spot have definitely become more aggressive over recent years and I believe the issue is related to the weather, you can call it climate change or whatever you like.

There’s no doubt in my mind that we see the undesirable combination of high humidity and high overnight temperatures more often nowadays year-round but also throughout the autumn and winter months. I used to think if we got to mid-November, we were past the worst but recent years have shown December to be one of the worst months for Microdochium activity. Furthermore this spring we saw active Microdochium from January through to May.

Spotting and reacting in the correct manner to those peaks of disease activity will be the challenge for all of us now we are bereft of contact, curative fungicides.

Worm activity

I am grateful to a Superintendent for sharing these above images with me (thanks Simon), though I’m sure he’d rather not have them present to share in the first place 🙁

With the loss of Carbendazim a number of years back now went with it our ability to control worms on outfield areas. I am of course cognisant that there are products used in our industry that cause mass earthworm ejection (lets call it that) and that there are still clubs using the aforementioned chemical (and some daft enough to advertise this on Twitter ???%&**??). The fact remains that it isn’t cost effective to use the worm repellent-type products on large areas for most golf clubs whether it is legal or not, but purely from a budgetary perspective and especially on the back of a Covid-19 year. As the photo above shows, wide-scale smearing on the turf surface is a real problem and this year it started early because of the very high soil temperature in August and the incidence of localised heavy rainfall that promoted huge amounts of worm activity during the second part of August in the U.K & Ireland. This has largely declined in the south and central areas with the onset of a very dry September and possibly across the east of Ireland and Scotland where I think (stand to be corrected here) it has been dry as well. For most of Scotland, the north west of England, west and south of Ireland, worm casting continues to be an issue though at least it’ll dry out a tad this week which will allow the casts to be brushed out without smearing (if you have the resource and machinery that is)

E.T, Plant stress and drying down time

Even though we are set for some hot September days with temperatures close to August levels this week, we won’t be set for the same high E.T levels.

As day length shortens going into the autumn / winter, the number of hours of sunlight does so as well and this affects wind generation, high temperature duration and of course evapotranspiration.

I’ve graphed out two 24-hour periods showing hourly E.T loss, one from the end of July this year, the other from the weekend just gone.

You can see how in the height of the summer, the E.T starts earlier and climbs faster reaching a peak value some 80% higher in July vs. September. The peak also extends longer into the afternoon / evening during the height of the summer whereas during September we see a progressive decline after 13:00 – 14: 00 hrs. Indeed in this comparison, the E.T is higher at 17:00 on July 31st than it was at 13: 00 on September 13th and the Davis Vantage Pro didn’t record zero E.T until 23:30 in July vs. 21:30 for the September day.

This has a number of consequences agronomically.

It means the level of plant stress is nowhere near as high as it would be in the summer, nor as prolonged. It also means dry down times for dew and worm casts are longer as the E.T level builds more slowly and to a lower peak, dropping off rapidly as the sun sets earlier. It also means you can get buy using less water because water loss is 45% lower on the September day than it was at the end of July.


OK that’s me for today folks, it is kind of nice to be back but all the same I’d still be as happy up to my nads in the Dyfi estuary chasing those very elusive Bass !!! 🙂

All the best.

Mark Hunt