Hi All,

It’s not difficult to see the effects of the very strong grass growth in May this year. Anyone who uses the roads will have noticed the tall grass growth around junctions and roundabouts that makes it impossible to see approaching traffic clearly. If like me, you spend a little time blatting about on a motorbike, you’ll have felt especially vulnerable in this case. Of course we have local cutbacks in budgets that must take some of the blame but for sure with the last 3 May’s showing a trend for increasing GDD, it must be a difficult task deciding how and when to target your limited grass cutting resources in this area.

It’s all change this week with a move to more unsettled conditions and a westerly airflow after 4 weeks of north / north-east dominating the weather. That means cooler, fresher even, some rain for sure, probably more for north and western parts initially and more consistent night temperatures. Let’s put some detail on it for the coming week.

General Weather Situation

A dry start for Monday for most, but there’s going to be some rain around with a thicker cloud base over Central Scotland likely to bring drizzle to the party and then later some heavier, more localised rain. As we go through the morning the heavy mist burns off to produce a warm, sunny day with temperatures rising rapidly into the mid-twenties for the south of England. Ireland looks to continue a nice run of weather with a dry, warm and sunny day. By late morning however we will see some rain showers push in to the north-west, north and possibly South Wales, The South West and north of England. This doesn’t really move much and if anything becomes lighter and more dispersed through the afternoon, as does the cloud cover. Now with moisture and rising temperatures we are sure to see some showers kick off later in the afternoon and the advice as always is look at your rain radar. Temperature-wise, mid-high teens for Scotland under that cloud cover and pushing up to the mid-twenties across the south of England. The wind will remain north-easterly through Monday.

Tuesday looks a cooler one with more in the way of cloud about for all the U.K and Ireland. It’ll be reluctant to burn off as well on Tuesday so that’ll keep the temperatures down a tad on Monday. Maybe the south-east of England will see the best chance of this occurring and if it does, here temperatures will push up into the twenties again. Dry again on the whole though late in the day you’ll feel that north-east wind start to shift to south-east and then by the time you next awake it’ll be south-westerly.

Onto mid-week already, how time flies when you are enjoying yourself. So everywhere will wake up to south-westerly airflow on Wednesday and with it arrives the first rain front from the Atlantic pushing into the west of Ireland early in the afternoon. East of this across Ireland and the whole of the U.K, you’ll have a dry and cooler start with plenty of cloud cover in situ. That rain over the west of Ireland will be heavy at times crossing Ireland through the course of the evening, maybe not reaching Leinster and the north-west coast of Scotland until midnight. So dry, cloudier and a little cooler for everyone on Wednesday, temperatures in the high teens, possibly nipping into the low twenties down south.

By dawn on Thursday morning that rain front will be into the west coast of the U.K bringing potentially heavy rain to Western Scotland, the north-west of England and North Wales. Ireland meantime will see lighter rain showers to start their day. By the start of the morning rush hour the rain will have moved across all parts of the U.K towards the east coast, lessening in intensity as it does so. By mid-morning the rain should have cleared Ireland and be more broken up across western coasts, with the heaviest now across the east and south-east of England. For some areas this will be the first rain for two weeks or so. By the afternoon that rain should have cleared east to leave a sunny and warm end to the day for many, though still with the risk of showers across the north and south-west coasts of Scotland.Temperature-wise, pretty similar to Wednesday, despite that rain, so that’s high teens for most and maybe nudging twenty degrees again down in the south of England. Winds will be moderate to blustery and south / south-westerly.

Friday sees us end the week with a dry (ish) picture for most places though with plenty of cloud cover courtesy of a weak rain front that’ll push some showers into the west of Scotland, the north-west and west of Ireland later on Friday morning. South and east of this we look to have a cloudy but largely dry day with some hazy sunshine. By lunchtime that rain will be into Donegal, Connacht and the west coast of Scotland but it’ll be slow to move inland during daylight hours when it is joined by another rain front. Scotland though may see some rain push into central areas for the second half of the day. Temperature-wise, mid-teens under that cloud and rain and high teens, maybe just nudging twenty degrees in the south of England. Winds will be light to moderate and south / south westerly.

With rain fronts coming in from the west late on Friday it’s no surprise then that the outlook for the coming weekend looks unsettled with rain fronts and thick cloud crossing Ireland and the U.K during Saturday. Sunday looks much the better day of the weekend with lighter winds, hazy sunshine and largely dry, save for some showers across the north-west of Ireland and Scotland possibly.

Weather Outlook

So next week looks like starting unsettled with low pressure in charge and this may potentially bring some strong winds and rain across the north and west of Ireland and Scotland through Tuesday. Further south we look to hold onto some drier weather courtesy of high pressure that pushes the low further north so not a bad week at all once the unsettled conditions have departed. At this stage I don’t think it’ll be ridiculously warm, pretty similar to what we have had, low twenties that kind of thing but with a low north of us and high across the south, they’ll be quite a contrast in temperatures as you move north. It could then quite possibly be a dry June as this weekend is the only rainfall on the radar for south and central U.K at present long-term. Time will tell.

Agronomic Notes

Ok, so a week later than normal, here’s our round-up of how May 2018 shaped up across the U.K and Ireland from a growth perspective.

May 2018 – GDD Analysis – Location – The Oxfordshire, Thame, U.K

After the dismal spring that we ‘enjoyed’ up until the middle of April this year, May 2018 came in as a very good growth month indeed, second only to May 2017 in terms of total GDD. In fact the last 3 years have been the 3 highest consecutive GDD totals for May, which kind of makes you wonder doesn’t it. A very good growth month isn’t great news for everyone because keeping outfield areas under control has been an issue but on the back of memories of a truly depressing March and first part of April, I think we will take it 🙂

It’s no surprise that cumulatively for the year we are well behind 2017, courtesy of that Sudden Stratospheric Warming Event in late February this year and unless we get a barn-storming July and August and / or a warm autumn, I can’t see us setting any records for total GDD this year.

May 2018 – GDD / Rainfall Analysis – U.K Locations

The locations show a very similar rainfall pattern across the entire U.K with the east side of the country the driest I think. (Lincolnshire I know was around 18mm for May)

More to the point with the torrential downpours of late May, most places received 50% of the total months recorded rainfall over a 24-hour period and in some extreme cases, all of their months predicted rain in a 3-hour period ! 🙁

May 2018 – GDD / Rainfall Analysis – Irish Locations

Now it’s not often that you see Irish rainfall totals lower than totals from the U.K, but looking at the easterly locations of Dublin and Johnstown Castle, Wexford, we can see 16.8mm and 33.2mm respectively.

That is one dry month from an Irish perspective !

Even 60.4mm in my beloved Co. Mayo is a pretty dry month, but looking back at last year, it was pretty similar, May 2017 was a dry month as well.

GDD-wise, Limerick looks to take the prize for being the warmest location otherwise all locations are very similar, just like most of the U.K ones, which indicates settled and consistent weather conditions throughout most of the month of May.

We also see the same pattern in rainfall totals with those thunderstorms at the end of May contributing 1/3rd of Cork’s rainfall over a 24hr period and 4 days of rainfall contributing 2/3 of it. In other words, a dry month in terms of number of days with no rain and then a small number of days with high daily rainfall courtesy of storms.

Monthly totals don’t tell the whole story…..

On balance May 2018 looks a pretty nice month from a turf management perspective but the storms at the end of the month brought a tricky combination of high temperature, highly localised rainfall and high humidity.

You can see this in the two graphs below from Swindon and Cork, featuring daily GDD and rainfall….

So in both locations we can see some real peaks at the end of May with daily GDD exceeding 12 (in my books this constitutes a growth flush) accompanied by high daily rainfall totals.

I didn’t manage to analyse how much nitrogen was contained in the rainfall that we had during those storms at the end of May but the fact that they were accompanied by lots of lightning suggests that it may well have been in the region of 1-5kg / N / Ha / inch of rain.

What happens here is that the energy contained in lightning is high enough to break the bonds of nitrogen oxide molecules present in the atmosphere (remembering that air contains 78% nitrogen) allowing it to combine with oxygen to form nitrate N (NO3) which is plant-available. So we get a lovely green up after a thunderstorm in part because grass receives a dilute liquid feed.

In the past I have measured amounts of nitrogen in rain water and then done the calculation working on the fact that 1″ of rain represents 254,000 litres of water over a hectare (shocking mix up of units there which I put down to my split parentage of Danish-English).

If you then measure the N content of the water, you’ll get a figure in mg/l so you can just multiply up to get kg / N/ hectare. I have worked out that if you have a total N figure in mg/l, then you multiply it by 0.254 to convert to kg / N/ Ha / per inch of rainfall.

So in the past I’ve typically measured 0.75-1.0kg / N/ ha per inch of rain (25.4mm odd) but during some trial work in Ireland way back in 2007 / 2008, I measured nearly 5kg / N / Ha (per inch of rain) that was deposited in some August storms. (Some of you will remember it because most of Dublin was flooded and the flood water was cascading off Croke Park Stadium roof like a waterfall !)

Agronomically what we saw at the end of May / beginning of June was a surge in growth, particularly in Poa-dominated swards and a ‘puffy’ turf habit indicating a succulent leaf and a fast growth rate.

This made it difficult to keep green speeds sensible at the end of May, beginning of June because the grass growth rate was so high and the sward was soft.

It also made it very easy for fungal pathogens like Microdochium nivale to attack the grass plant and that’s why we saw such aggressive Microdochium across swards during late May / early June.  A combination of a thin leaf epidermis (because of fast growth rate) and long periods of elevated plant leaf wetness (because of high humidity)

I also think this surge of growth was too much for PGR to hold back as I had a number of reports of excess clipping yield even when a PGR had been applied.

Anthracnose Trigger ?

Now that the gliche in Weather Underground has been fixed I’ve been able to look at some different sites across the U.K and Ireland to determine if we had the correct combination of conditions to trigger spore germination. You’ll remember from past blogs that with this disease it is air temperature around 25°C for 2-3 days combined with high humidity around 87.5%. (marked red below)

So I’ve down a lot of data trawling, one of those jobs that you start and then wish you hadn’t because it has taken hours to sort.

Now the data below comes with lots of caveats, not least that I’ve lifted weather station data from around Ireland and the U.K and so much depends on where that weather station is situated. It also depends on whether the location received one of those heavy storms as well to generate the humidity.

Caveats aside, It does at least give a flavour as to which areas have had the necessary temperature and humidity combination for Anthracnose disease development to be initiated.

Now you’ll remember that even if this particularly disease is initiated it doesn’t necessarily follow that you’ll see symptoms develop later in the summer because the plant has to go under stress, usually from high temperature / high E.T. This data does serve as a line in the sand though that some areas have been warm and humid for long enough to start the ball rolling. If we do get high temperature stress in the future then I’d expect to see symptoms from the beginning of July onwards, perhaps more so toward the middle / end of July.

Ok my head is frazzled, that’s it for this week, time for a cup of Earl Grey and a lie down….

All the best…

Mark Hunt