I got sent this cracking weather-related picture from Sean at The Oxfordshire late last week and it reinforces the changeable nature of the weather at the moment, a few days dry /warm, a few days wet.
That Mackerel skies weather saying keeps buzzing around my head after happening upon it last week. Sure enough as I sat outside yesterday evening and looked up at the cloud base, there was that Mackerel sky made up of Altocumulus clouds. It’s not just well-known here, in Germany and France it is known as a ‘Sheep Sky’ (German: schaefchenwolken; French: nuages moutonneux). The week past we had some warm weather, high E.T days but also some rainfall as well, so that changeable theme for summer 2020 continues. I for one much prefer this to a balmy heatwave any day of the week, plus it is good for growing grass, exercising and also for fly fishing 🙂
So as we start another week, the images above highlight the pretty good accuracy of the GFS forecasting platform, the top image is the actual weather pattern for today and the bottom image is the projection for today from a week ago, not bad I say.
As you can see we still have a jet stream boundary sitting across the U.K and Ireland, when this boundary is pushed northwards then high pressure dominates our weather, when it is pushed southwards then low pressure dominates. This is the cycle of weather we have been in since early June and one that looks set to continue as we see out July and tip toe into August.
General Weather Situation
So from the projection above you can see we start the week with a north-south split. High pressure is edging into the south of Ireland and southern half of the U.K whilst the north and Scotland picks up some of the cool, fresher and wetter weather, courtesy of a low pressure system sitting close to Iceland.
For Monday then we have a pretty settled weather picture, sunny in the south with cloud cover pushing in across Ireland, Wales and the north west of England and further north, rain across the west of Scotland that will move eastwards through the day. As we move through the day that cloud cover increases and it may just set off some showers across South Kerry and the north east of England. Further north that rain over Scotland intensifies and brings heavier rain to the north east and east of Scotland later in the day. Temperature-wise, mid-teens for Scotland, high teens for the north of England, Wales and Ireland and just nudging into the twenties across the south. Winds will be light to moderate and from the north courtesy of that leading arm of the high pressure pulling down northerly winds.
Tuesday sees almost a carbon copy start to the day, dry everywhere except the north west of Scotland. Brighter to the west and across Ireland during the morning but as we approach the afternoon we see more heavier cloud cover push in from The Atlantic. This thicker cloud is courtesy of a rain front pushing in from The Atlantic and likely to bring rain overnight to the north west of Ireland and Scotland. So a calm, pleasant and settled day across England, Wales and Ireland for Scotland much drier than Monday and a tad warmer as well. Those winds will still be light to moderate and northerly-orientated for most of us so that means a similar temperature spread to Monday, high teens to low twenties.
Mid-week beckons and overnight that rain front has pushed across the north west of Ireland and into western Scotland, really anywhere from the beautiful island of Arran northwards. So a cloudy start across Ireland, wet for the north and north west and the same for Scotland. Further south we look to enjoy another calm and settled day with long spells of sunshine, some cloud cover and pleasant temperatures…’perfic’ 🙂 Through the course of the morning that rain front over north west Ireland heads south and east across the country and likewise that rain over Scotland moves south into The Borders and the north of England. By late afternoon though it looks to fizzle out to a showery scenario stretching across Ireland, the north and west of Scotland and England. There’s a possibility of some of these showers heading down into North Wales and the north midlands. A little warmer on Wednesday as those winds drop round to the west so expect temperatures to edge up into the low to mid-twenties for Wales and England, mid-teens for Scotland under that rain but Ireland will at least have some warmer spells between the rain and temperatures nudging into the twenties.
OK, onto Thursday and we start the day with thick cloud and a line of heavy showers stretching across Ireland, North Wales, the north of England and Scotland (particularly the north and west again here) As we move through the morning those showers will slowly push south into The Midlands and Mid-Wales clearing the west of Ireland as they do so. South of these showers it looks to continue warm and dry as this area hold onto the warm weather but through the day those showers will continue to push southwards on a fresh to moderate westerly wind. So an unsettled day for most with temperatures in the high teens to low twenties in-between the band of showers. As we approach dusk most of the showers have fizzled out leaving a vestige along the east coast of the U.K.
Closing out the week on Friday on what hasn’t been too bad a week weather-wise, the theme is dull and dry for almost all of the U.K and Ireland. They’ll be some brighter spells across the east of Ireland and Wales, The South West, but most places will be dull and dry for the majority of the day with the wind swinging round to the north. The thicker cloud cover and change in wind direction will knock the temperatures down on Friday so expect high teens as the norm. Later in the day we will see showers push into the west coast of Ireland as an Atlantic low pressure system starts to make its presence felt. These showers will track east across Ireland on Friday evening.
So an unsettled and cooler end to the week, how does the weekend look ?
Well Saturday looks pretty unsettled now with that rain having moved across The Irish Sea overnight into Wales, the west of England, northern England and Scotland. That same rain band will still be affecting Ireland throughout Saturday with plenty of showers around and principally it’ll be dull. Sunday looks similar, maybe less showers around initially but they’ll soon pop up and coalesce into longer spells of rain for Ireland, Wales, Scotland and most of England. For both days maybe the far south east of England will be the least rain-affected. Later on Sunday we could see the intensity of showers reduce over southern England and some brighter spells but all the time unsettled is the theme you should take with you for the weekend. Mid to high teens the order of the day for the U.K & Ireland with the highest temperatures down in the south as usual. The wind will swing round from northerly this week to westerly / south westerly for the weekend and take on a fresher feel alongside that rain.
Mackerel skies…Mackerel skies…
So the projection for the start of next week is for the jet stream to have dipped south with the arrival of a new Atlantic low pressure system. As you’ll hopefully have gleaned by now the outlook for next week is quite the opposite of this week with low pressure pushing rain into Ireland on Monday and then this moving across The Irish Sea into the west of the U.K through Monday a.m. / p.m. So rain across the U.K for the second half of Monday and into Tuesday. A brief respite before more rain arrives on Tuesday into Ireland and again pushes eastwards. The low intensifies on Wednesday to bring potentially stronger winds and heavier rain before backing off at the end of the week with just showers for Thursday and Friday. Now since these are Atlantic low pressure systems it means the bulk of the rain will be north and west. We will know closer to the time if the low is more likely to track southwards or northwards. Either way, work on an unsettled week and you won’t be surprised.
E.T / Soil moisture deficit / Rainfall Situation
So first up I thought I’d kick off with an update on where we are tracking rainfall and E.T-wise 2020 vs. 2018. Over the weekend I was fly fishing, this time enjoying a brilliant session at Draycote reservoir near Rugby. In the queue for the only loo open by the fishing lodge I was looking at the reservoir stats when one of the other people in the queue remarked “No hosepipe bans this year then” as the reservoir was at nearly 100% of capacity. In this scenario, the 5 months of near continuous winter rain had been put to good use but of course for the majority of golf courses and the like, this isn’t the case. Back in early June you may remember, I was really worried, we were on the back of a continual dry spell with high E.T, Poa was on its backside and water reserves were rapidly dwindling. Worried because we hadn’t even started the summer proper and facing the potentially hottest months ahead of us.
Fast forward to today and I’m a little less worried, July 2020 will pass by with a reasonably high E.T and actually not that far behind July 2018 all things considered up until today’s date.
The biggest difference, as always, has been rainfall.
Here’s a comparison from June 1st to July 19th inclusive of 2018 and 2020 using data from The Oxfordshire location.
Year Total E.T – June 1st – July 19th Total Rainfall – June 1st – July 19th Deficit / Surplus
2018 196.9 mm 2.4 mm – 194.5 mm
2020 166.1 mm 88.4 mm – 77.1 mm
As you can see the big difference is the rainfall and so if we look at the potential soil moisture deficit, it’s roughly a third of what it was in the summer of 2018. Happy days….
Here’s the actual stats till July 19th using the same location….
So you can see the two lines are rapidly closing up on each other and if next week’s unsettled weather pans out as forecast I wouldn’t be surprised if by the end of this month they are pretty much equal. Good news really for us, less stress both on the grass and us personally in what has already been a pretty uniquely challenging year. And one that hasn’t yet finished with all of its surprises I think…
So I am seeing a lot of these pictures finding their way into my inbox or on social media and the like.
It is tricky to definitively diagnose them on turf appearance only because on first sight this could be Spiral nematode damage, Anthracnose or Take All or perhaps a combination of both nematode and fungal pathogen. Now most people will instantly dismiss Take All because they’re managing a Poa-dominated sward but this wouldn’t be a safe assumption as I know Kate E has been diagnosing Take All on Poa. annua for a good while now. Take all attacks the plant root and often does its damage long before you ever notice a symptom. It is only when the grass plant begins to suffer high E.T stress that you see the consequences as the plant struggles to maintain adequate water status through a damaged root system and leaf die-back occurs. So if it were Take All, you’d normally expect to see symptoms after some pretty toasty high E.T days, that’s your first marker and for me anytime from mid-June onwards typically with its season of activity extending into the autumn if we have a wet summer. Take all tends to follow a more classic fungal patch sort of shape as well in my experience whereas Anthracnose tends to be more vague and irregular.
Now I’ve talked about Anthracnose back at the end of May and also during that mini-heatwave we had in June but I have revisited some temperature and E.T stats for a recap.
This time they’re from the Sevenoaks area of Kent for a bit of variety.
Now this is a complicated graph, it took me about half an hour to get my head round it, split the axes over the same time frame (1st May – 19th July, 2020) and then annotate it. I think some people imagine I have hordes of colleagues who I can just ring up and said “Err knock me out a temperature and hourly E.T graph please for this location and annotate it with dates and threshold settings…and have it in my in tray by 10!.”
Ha ha I bloody wish….Even if I did have, my mind is so scrambled on a daily basis that these thoughts kind of come into my head as I’m thinking about where we are, what’s relevant and often, your feedback…That’s what sets the tone for this blog usually so preparing a grpah like this in advance isn’t an option 🙂
So I think it is also a pretty interesting graph.
Reporting the hourly E.T is something quite different from a daily total but the reality is in my book if I see more than 0.5 mm per hour E.T loss then the plant is under stress and it is likely to be a high E.T day. Bearing in mind that on a stressy day, E.T can start building from 07:00 a.m. and continue on through to 20:00 p.m. reaching a peak at 13:00 / 14:00 p.m. Anything above 0.5 mm hourly E.T loss will typically end up with a daily total > 4.5 mm over a 24-hour period. Now that’s stressy.
Looking at the top graph we can see we had some serious periods of E.T early in the summer and these coincided with Poa. annua seedhead production. These periods effectively extended the severity of the Poa annua seeding period. Normally it starts early May and continues for 6 weeks before subsiding (but not totally), whereas this year we saw some heavy seedhead production from Poa. sp late into June / early July because of the mini-heatwave that occurred at the end of June.
If we look at the bottom graph (temperature) we can see we had two periods when the air temperature edged above 25 °C, the first between 19/05-21/05 and the second more prominent peak occurring between 23/06 – 26/06. Now this period also coincided with a high E.T peak so we know that grass plant was under stress at this time and that conditions were high enough temperature-wise for Anthracnose spore germination. Not shown on this graph is the rainfall that followed this period and the rise in humidity so in other words in my mind it’s this late June period that ticks all the wrong boxes when it comes to Anthracnose. That we are now possibly seeing turf symptoms 3 – 4 weeks later also fits the bill because we know it is a slow-growing fungus and has two distinct phases of fungal development. Firstly the biotroph-phase where the spores germinate, produce fungal mycelium and these enter the plant leaf surface. We know it can sit in this primary biotrophic development stage for a significant period without damaging the plant. Then when the plant goes under stress we see it shift to the necrotrophic stage where it begins to invade cells within the grass plant and kill them and for the turf manager we see symptom expression. Now a lot about this fungus is still to be determined but we know the first phase needs high temperature (above 25 °C) over a continual period along with or followed by high humidity and plant leaf wetness. The second phase is harder to pin down in my mind because some years we see the trigger conditions but no symptom expression and here we can only surmise that conditions weren’t conducive for the fungus to transition from biotroph to necrotroph.
We also know largely by the excellent work done at Rutgers University that a number of cultural factors affect the severity of the disease in terms of expression including low N and low K plant leaf tissue nutrient status. Putting the plant under stress by reducing the cutting height (< 3.2 mm) and / or lowering the irrigation level / nutrient status are recognised triggers. It comes as no surprise then that combating Anthracnose aside from applying a preventative fungicide comes down to keeping the grass plant healthy, maintaining adequate (but not excessive) plant tissues levels for N and K (>3.6% and 2.0% respectively) and not increasing the plants stress level.
Now symptom expression is also governed by your grass species with less Anthracnose prevalence on Bentgrass, so if you have a mixed Poa / Bent sward you might minimise the severity of expression by overseeding bentgrass. If you’re using a U.S-sourced bentgrass then you should be able to ascertain cultivar Anthracnose sensitivity from the trials they conduct there.
Some forms of cultural work have often been associated with increased Anthracnose including summer topdressing and verticutting but in the work conducted by Rutgers they found precious little evidence of this and indeed quite the contrary when it came to topdressing. In their research work they show a great image (below) of how the grass plant crown is protected by topdressing and so less sensitive to temperature extremes. Also a firmer surface means that their is less of an issue when comparing bench set with actual height of cut. In other words, a softer surface tends to allow the mower to sit down into the turf surface and therefore cut lower which in turn puts the plant under more stress.
A compelling argument for good surface organic matter management and topdressing me thinks 🙂
So if you are seeing symptoms, keep nutrition up, maybe undertake a little overseeding of an cultivar mix that isn’t sensitive to this disease, keep up the topdressing (as this tends to help in-fill and also maintain a smooth surface) and above all maintain adequate nutrition so the plant isn’t ‘hanging’.
OK that’s me done for this week folks.
Enjoy the pleasant week, all the best.