August 6th

Hi All,

As we enter our 10th week of pretty continuous hot and dry weather, we have a change on the way as correctly predicted last Monday with some cooler and unsettled weather on the cards. That’s precisely what awaits me in Alaska with some pretty significant low pressure systems doing the rounds and plenty of bears across the river from the camp feeding on Wild Blueberries apparently. Should be interesting……

It is a change that won’t be welcome news for farmers maintaining crops like this and as I noted the dust clouds rising over The Welland Valley yesterday whilst out walking, I sensed urgency in their work. Like our industry, they have had a very challenging year, cold winter, wet and cold spring, driest, hottest summer, you know the thing. For sure it is already causing an impact as you see cows and sheep being fed hay in the fields because the grass growth is insufficient for grazing. I ground up an ear in my hand from the wheat field on the right and the grains were really small, lots of screenings this year and for sure lower yields of grain and straw, so we will see this in our pockets when bread and milk prices rise.Their industry is already incurring significant extra costs and will likely lose money on poor yields, but what of ours ?

It made me think about the effect of this years weather on our industry over the course of the year, for sure a loss of rounds and revenue early on with the wet spring and winter snow closures. Since then it’s surely been good from that perspective with less issues regarding playability, less cutting, more watering, less disease pressure (less humidity), poor Poa growth, more seedheads, good bent growth, I could go on… It is ‘swings and roundabouts’  on our side of the fence.

All in all though has a long run of dry and hot weather been negative do you think ?

I wonder if we will carry some sort of legacy into the autumn with a grass plant that’s been on the back foot for such a long time and I also wonder in a year of extremes, what the autumn will bring weather-wise ?

Will we sign off 2018 with the warmest, wettest autumn ?, lets hope not and no I haven’t a clue at the moment.

General Weather Situation

So we start the week as we finished it with another hot, dry day for England and Wales on Monday. We have low pressure sitting north-west of the U.K and the above Meteoblue image shows the typical demarcation line when it comes to cloud and rainfall of late with Ireland, Scotland and north-west England ‘enjoying’ thicker cloud cover and cooler temperatures. So a cool and showery day for Scotland with some light rain, mainly across the west, Ireland pretty dry but cool under that thicker cloud front and England and Wales set for another extremely hot day. I expect temperatures again in the high twenties, low thirties today with a gentle wind from the west, increasing in the afternoon as convection sets in. High teens for Ireland and Scotland.

Onto Tuesday and a very similar picture with the thicker cloud base and rain following the same pattern as Monday. Maybe more chance of some rain across the north-west of England and east of Scotland for a time on Tuesday morning, but this fizzles out to leave just thick cloud cover. A dry, cloudy day with perhaps some breaks in the cloud for Ireland during the afternoon but rain will push into the west just before midnight. For England, a re-run of Monday, hot, dry and sticky but already the impact of that cooler air pushing in from the west will be felt across Wales with temperatures down in the low twenties for the day. For England we will see similar temperatures to Monday but there’s a risk of moisture pushing in over The Channel into the south-east and east of England and this could trigger off some thunderstorms possibly. This threat of thunderstorms may extend up into The Midlands but we will see.

Wednesday sees a rain front pass across Ireland overnight so by dawn it’ll be departing Leinster most probably. This rain front will push eastwards into The South West, West Wales and the west of Scotland through the morning intensifying as it crosses land mass. Further south this rain won’t make much more progress inland confining itself to Wales, The North West, The South West and Scotland. So England is set for a sunny day with hazy sunshine but much lower temperatures than Monday and Tuesday, down in the low twenties with a freshening westerly wind. That drop in temperatures will be felt everywhere with Ireland and Scotland now in the mid-teens, Wales and England, high teens to low twenties and significantly for the latter, much cooler nights to make sleeping more bearable.

Thursday sees a similar picture with rain fronts stacking off the west coast of Ireland and through the day these will make slow progress across the country, initially affecting West Munster, Connacht and Donegal during the morning but pushing inland later in the afternoon. For the U.K, we will also see rain across western coasts during the afternoon affecting an area from South Wales upwards. So England looks to stay dry on Thursday with again some sunshine and cloud and little in the way of rain away from western coasts. Scotland looks to have some pretty wet weather across the west and this will stay confined to the coast till the afternoon when it’ll move inland. Similar temperatures for all areas to Wednesday, mid-teens for Ireland and Scotland and high teens, low twenties for Wales and England. A fresh westerly wind again in situ.

So we close out the week on Friday with another very unsettled day, particularly across the west with some rain across Ireland, The South West of England and Scotland from the off. This rain could push into The North West and northern England through the course of the day and move along the south coast of England later in the afternoon into The South East on Friday evening. I’d say more risk of showers moving inland on Friday accompanied by a strong westerly wind but saying that many areas will stay dry and see some sunshine. Similar temperatures to the rest of the week with that strong to moderate westerly wind bringing a much fresher feel to the weather.

The outlook for the weekend isn’t great really unless you are fed up with irrigating and trying to keep your garden and lawn alive that is at home 🙂 So a heavy front of rain is set to push across Ireland and Scotland on Saturday crossing into The South West and Wales during the late morning pushing thick cloud before it. So the 2nd part of Saturday will see heavier rain for the west of the U.K moving inland as it does so with Ireland and Scotland hanging onto that rain for most of the day. (maybe lighter across the west of Ireland). That rain is set to cross the U.K overnight into Sunday with more rain likely through the day further inland across England a.m. with Ireland and Scotland missing the worst. Strong westerly / south-westerly winds likely over the weekend associated with that rain system and these will ramp up through Saturday before dying down through Sunday as the low passes through. Similar temperatures across the weekend to the 2nd half of the week.

Weather Outlook

So with the onset of unsettled and cooler conditions for the 2nd half of this week and weekend is this a fixed change or just a flip of a coin that will flip back to the hot and dry side next week ?

Well it looks like the latter from where I am sitting with the cooler front set to stay till mid-week next week before high pressure re-asserts itself from the west though not with the same level of heat as we have seen this week. I think after next weekend we will see a sunshine and showers scenario for the start of next week, more in the west and north rain-wise and staying cool with the winds more northerly if anything. Wednesday next week looks interesting and possibly another front of heavy rain pushing down across Ireland and into the rest of the U.K before high pressure spins us back onto a drier and warmer outlook.

Grass Agronomics

Ok since it’s my first blog of August we will do our normal look back at July GDD from a stats perspective.

GDD Comparison – Thame Location

Not surprisingly perhaps for a measurement that averages maximum and minimum air temperature, that our GDD figure for July 2018 was the highest we have ever recorded at 434, that’s 10% higher than any other July. Of course it doesn’t mean that we have recorded record growth because other factors will have come into play, namely moisture limiting growth and also the maximum air temperature being too high for the growth of some plant species, namely Poa annua, more on that later.

So the cumulative for the year looks not bad really and courtesy of July’s heat, 2018 is no longer a poor partner to the other years as it was before. In fact 2018 sits only just behind 2017 now as the highest GDD year cumulative July, what’s the betting that it doesn’t finish up as the warmest 2nd half of the year ever maybe ?

GDD Comparison – UK Locations

Ok let’s look at the GDD stats for the U.K and Ireland, accepting the fact that my weather station spends some of the time in full sunshine, so I get an ‘enhanced GDD’ figure.

Market Harborough is a lot of things but it isn’t the sunshine capital of the U.K, I think that title belongs to Eastbourne or somewhere similar. Incidentally my esteemed colleague Andy Russell hails from Eastbourne. It is rumoured that he only lives there because everybody else is older and that makes him feel young. (Luckily he never reads this far in my blog so I’m safe with this assertion :))

So pretty high GDD’s as commented earlier and you can see the difference a cooler airstream makes when we look at the Fife total and the Irish locations below. Rainfall-wise it’s a case of the ‘haves and have nots’ as commented in previous blogs with mid-teens for the month pretty standard and the higher totals for York and Okehampton courtesy of more rainfall during that cool and wet period at the end of July.

GDD Comparison – Irish Locations

Above are the stats for the various Irish locations and you can see the effect of a cooler westerly air stream that kicked in periodically during July across Ireland and is still in place today (same applies to Scotland). That said July 2018 will go down as a very good month from an Irish summer perspective and follows on from a very dry June where temperatures were very good but not as high as July.

Cumulative E.T Stress – Summer 2018

First off, I have updated the E.T vs. rainfall stats from The Oxfordshire (cheers Sean) so we can see how we are tracking. Now I know for the north and west (as per Meteoblue graphic model) you’ve had more rain and so this is largely immaterial but for England and Wales, the drought continues.

First up don’t they look very different graphs !

So if we look at the above stats taking the two-month period from June 1st to July 31st, in 2017 our soil moisture deficit was -113.9mm and in 2018 it is -225.1mm, a gnats whisker under double the moisture loss this year than last. Consider also that we have had some very hot days since and I think the E.T loss will be > -250mm over the last 9 weeks, that’s 10″ of rain equivalent !

That’s the result of 132.7mm of total E.T loss in July 2018 vs. 103.7mm in July 2017 for this location, an average of 4.3mm E.T loss per day. Of course it’s rained less this year as well with 16.4mm of rain in July 2018 vs. 62.2mm in July 2017.

Just while we are on the subject of stats from The Oxfordshire, the average maximum air temperature for July 2016 was 23°C, for 2017 it was 23°C and for 2018, 26.0°C. So the average maximum air temperature was +3°C, that doesn’t sound very significant does it but it is.

Consequences of prolonged E.T stress.

Growth Patterns

Well we know that during July in particular, the maximum air temperature has exceeded the limit for growth of Poa annua. Now it’s pretty tricky to find definitive data regarding what the ‘top out’ temperature for Poa annua is and maybe a little irrelevant because presumably a Poa annua biotype growing in the U.S will be different from one growing in say Dublin.

If I picked a figure I’d say that anything above 27°C has Poa annua on the back foot and whilst it won’t stop growing totally, there will be a marked drop off in growth rate. So I’ve plotted out the maximum air temperatures for the Thame and Dublin locations and looked at how this potentially could have affected Poa annua growth.

I’ve blocked up the days in red where the temperature was either close to or exceeded 27°C and you can clearly see the difference between the two locations. Now Thame is by no means the highest air temperature U.K location, so I’d say the stats for Surrey would have been even more significant. You can see the difference for the Irish location in that although they have had a very good June / July (depending on your perspective), the effect of maximum temperature on Poa growth was much less suppressive.

So during July at the Thame location, we have 18 days out of 31 when Poa annua was potentially growth-limited by maximum air temperature. It should also be said that if your surfaces have a higher organic matter content, they will have heated up quicker and so the effect would be even more significant.

I would also expect that if I ran the Growth Potential stats for July I’d see a reduction in G.P on these days. One of the big benefits of using G.P vs. GDD is that the equation takes into account the optimum temperature for cool season grass growth and produces a lower figure at higher air temperatures. This serves as a very good indicator of plant stress.

This feature of G.P is highlighted in the Meteoturf module this week with a lowered G.P for Monday and Tuesday courtesy of the high air temperatures and then an increasing G.P as the cooler air arrives mid-week. (see below)

What could be the consequences of this reduced growth potential ?

Organic matter production

Well less growth means less organic matter production for one and less nutrient use as well because the Poa plant isn’t developing new shoots, existing effectively in shut-down mode. It is also worth pointing out that with the high temperatures Poa annua switches over to survival-mode and that’s why we have seen another seedhead flush at the end of July / early August on fine turf.

From a practical perspective it would also mean less requirement for vertical aeration (verticutting) and topdressing (because there’s less growth to dilute). I always remember the sadly late Dr. James Beard commenting that a clubs maintenance schedule should not be fixed year on year in terms of aeration frequency, type of aeration, nitrogen input and in particular topdressing. It follows that in a growing year, there’s more requirement to keep organic matter under control by aeration and topdressing, whereas in this type of summer, that requirement must surely be less ?

August Aeration, root development and overseeding

Always a controversial subject for sure but one worth visiting….

Another consequence of the sustained temperatures will be a loss of rooting as the plant ‘sacrifices’ surface roots vs. deeper roots (if it has them). Now this last observation is purely anecdotal because I haven’t pulled plugs lately but I would expect root development to be pretty limited during extended periods of high air and surface organic matter temperature.

If this is the case then I think one of the benefits of August renovation is surely restoring some of that root deficit provided it coincides with cooler conditions. Another benefit is speed of germination if you are also using the opportunity to overseed as part of the aeration process. I put down some ryegrass seed on Thursday night and noted it had popped yesterday afternoon, that’s 3 1/2 days !. I presume bentgrass overseeding carried out at the moment would show a similar speed of germination.

Rainfall flush

Another comment that I have picked up repeatedly over the last week or so is the degree of growth flush experienced at the end of July once the rain arrived. Now I theorised about this last week in terms of N input in rainfall and possibly a pH effect as well.

Dr. Micah Woods kindly put me straight on the topic of rainfall pH, in that the pH of carbonic acid (CO2 + H2O) at equilibrium is around 5.6. Typically though I measure rainfall pH levels higher than this (depending on the type of rainfall and its source) so I can only surmise that the reaction between CO2 and H2O doesn’t reach full equilibrium and / or possibly other atmospheric constituents of rainfall are affecting the pH ?

And Fairy Rings….

Another consequence of the rainfall at the end of July was enhanced activity of the Fairy Ring fungus and a change in the ‘behaviour’ of the ring. So the feedback has been of Fairy Rings sitting there through July but becoming very active once we had rainfall. As we know, that rainfall was followed by some very high temperatures and in some cases, this has caused a loss of grass cover / bleaching effect around the circumference of the ring.

Why is this occurring ?

Well I think that the Fairy Ring fungi becomes more active with the advent of rainfall and elevated humidity and this activity extends to a higher fungal growth rate. The image above shows the effect of active Fairy Ring mycelium on moisture repellency in that more fungal mycelium = greater hydrophobicity.

So the areas became more water-repellent and then shortly after, air temperatures and E.T rates increased markedly, so the localised requirement for moisture increased dramatically. These areas are harder to wet up and so unless you were applying a good quality surfactant (with good organic matter wetting abilities) and irrigation close to the above sequence of events, you’re likely to see plant stress and potential grass cover loss. I think the above process happens very quickly by the way.

There has also been some research to suggest that a build up of ammonium / ammonia as a consequence of the Fairy Ring fungus converting organic nitrogen to nitrate nitrogen can be toxic to the grass plant. I would have thought that in hot conditions it would more likely be ammonia gas toxicity due to volatilisation. For this reason, light aeration to vent surfaces is beneficial as will be the application of a soil surfactant with Azoxystrobin and a biostimulant prior to the onset of rainfall (like later this week perhaps)


Ok that’s it for me today and for the next few weeks, I have to finish off my in-tray, tie a few flies, chuck my stuff together and ship out to AK. I hope the weather (and the bears) play ball (mental reminder not to watch The Revenant again on the in-flight movie!) and I look forward to catching you on the flip side late August.

All the best…

Mark Hunt