15th August - a week of change

Hi All,

First up, many thanks for all the positive feedback on last week's blog, it is appreciated and very motivational for me, so thanks.

Well, I am delighted to see the first showers and thunderstorms rolling into the UK & Irish weather picture. For some it'll be the first rain for over a month in what is an unprecedented drought situation, not just here but across Europe. Almost half of the European Union is currently experiencing drought conditions, as is the USA. My pre-Covid bi-annual 'holiday' fishing destination, the wilderness of Alaska, is beset by fires currently as the tundra is crispy dry. For some many different parts of the world to be affected by record temperatures and drought at the same time, it does make you think if this is a portent of the future as our climate warms in an out of control manner, whilst our politicians tap their fingers nervously.

I was reading a great article produced by the BBC entitled "The science of drought explained in pictures" and this image caught my eye. Firstly, because of the dramatic loss of water and secondly because it is one of the most westerly reservoirs in Yorkshire. Some of the stats are amazing, I didn't realise for instance that the source of the River Thames has retreated 5 miles downstream for one. You can read the article here

So the media is already saying how the rain this week will fall in a torrential fashion in places leading to flooding and how this won't change the drought picture because the soil is bone dry and of course hydrophobic.

As turf managers we know all about hydrophobicity don't we and we have tools to maximise water infiltration so that for me is one job for this week. I saw a FB article the other day where Greenkeepers were discussing which wetting agent they used and of course there were a myriad of responses. One contributor described them as a 'poison' being applied to the soil. Now that's an interesting viewpoint bearing in mind that the longevity of a surfactant is largely determined by how quickly it is broken down by microbial activity and the role they play in maximising irrigation (and rainfall when we get it !) efficiency by facilitating water movement into hydrophobic soils. I was tempted to respond but I think the most obvious answer would be to see how much water you need to apply to an untreated hydrophobic soil to wet it and how inefficient that process is.

Back to this week and all I would say is that any rain is gratefully received. I remember the drought of 1976 finishing with torrential rainfall right at the end of August and how the river levels quickly responded because the initial rainfall did indeed run off a bone dry soil. We had a wet autumn in 1976 and it was that wet autumn that re-corrected the dry soils and aquafer levels back then. What chance of that this year ?

Pete Goss, from Ashbury Golf Resort sent me some data back from 1976 to show how the rainfall played out for one location (Southampton), cheers Pete, appreciated.

Onto this week's weather and what you'll notice (and have probably already) is the rapidly changing, predicted rainfall within forecasts.

Karl Gutbrod, founder and CEO of Meteoblue (the Swiss weather company that I have been a fan and follower of since they were a start-up) once told me that predicting summer rainfall was extremely difficult. This is particularly the case when it comes to rainfall from thunderstorms. To understand this, you have to understand the formation process that leads to a thunderstorm. It begins with an updraft of warm moist air from the ground. Now up until recently we haven't had any moist air to speak of because the air has been so dry.

The stats below show the relative humidity on a daily basis from 01-07-2022 for Thame, Oxfordshire and I've highlighted the two heatwaves. You can see how the relative humidity (the moisture content in the air) dropped to 27.5% in July's heatwave and 32.5% in the recent August heatwave. Another factor to mention is that the drier the air, the more moisture can be evaporated from the plant and soil (high E.T).

Back to the formation process of a thunderstorm. So we need this heat updraft of warm, moist air. Well this updraft can begin practically anywhere. It can be from the roof of factory buildings, cars parked at an event, concrete surfaces radiating heat upwards. Indeed I have shown in past blogs how storms have followed the line of motorways like the M1 and M40 because these areas are hotter than the surrounding countryside and 'fuel' warm air updrafts into the storm. Last week, I was driving home from a baking fishing trip and it was 28°C when I left. 2 miles later on the packed M1, full of middle lane jockeys, the air temperature shot up to 34°C ! (that could have been the resultant hot air from me swearing at the afore-mentioned though :) ).

That hot air rises, cools and forms into precipitation event. It is often characterised by the formation of an Anvil cloud.

Back in the days when I travelled around Europe a lot and had the 'pleasure' of multiple journeys courtesy of Ryanair (which I won't knock because you get what you pay for and without them I wouldn't have been able to travel), I remember flying into Luton airport from Nimes, France and noting the anvil clouds that indicated the beginning of the breakdown of summer 2018. I love this pic...

The fact that the hot air updraft can begin practically anywhere leads to the variability in the process and that's why this week's rainfall is going to be a tough one to forecast accurately, so I'm not even going to begin to try !!!

I will instead be glued to Netweather.tv and the Dark Sky app(I find the former more accurate rainfall radar-wise though) to try and determine if Market Harborough will get some.

General Weather Situation

So as we can see from the GFS GIF courtesy of tropicaltidbits.com, we have two low pressure systems across the U.K & Ireland. One is the BOB low pressure that popped up and effectively cut off the hot air plume, the other an Atlantic low that is slotting into the cool air trough created by the BOB. The projected rain pattern for the next 10 days (above caveat aside) is shown below in the animated GIF.

So this week we have a much cooler and unsettled theme, with some very welcome cool nights. Today is the last day of heat for the south and east of England but the change is already underway with rain across Ireland, Scotland, Wales and the north of England.

Frustratingly (and this is what it is going to be like so I feel your pain believe me) I can see storms seeding less than 8 miles away from me but they're likely to head in the wrong direction :)

So Monday through to Wednesday sees this slow-moving combination of low pressure systems push rain across the U.K and Ireland with temperatures dropping down to the low twenties during the day and mid-teens at night. The wind direction will be variable this week depending on your location and proximity to the low pressure systems. As an example, for my location, it is given as north westerly Monday / Tuesday, north easterly on Wednesday and then swinging round to south westerly for the end of the week. As we move through towards the end of the week, we see a weak ridge of high pressure push the rain more north but a northerly Atlantic high pressure will keep the heat further south and allow rain to push further south next week as well. So for the southern half of the U.K, I think Monday through to and including Wednesday offers the best chance of rain this week.

Weather Outlook

So above we can see the animated GIF for next week and how we start the week with Atlantic low pressure dictating the weather for the first half of the week. So we will see more rainfall from Sunday onwards for the north and west but this may push further south as well as the tail end of that low swings round. We then look to build heat towards the end of next week however there is another BOB lurking and this may still introduce moisture into the equation for the south of England so fear not, there's still a chance of rain later in the week.

The weather situation / outlook is delicately balanced but for now we look to have settled down into an Atlantic low pressure then high pressure then Atlantic low pressure sort of pattern because the position of the jet stream has shifted south and that allows a more Atlantic theme to our weather for the 2nd half of this month. As I said last week, this won't be a drought ender and indeed we could build heat again for the end of the month but I think it is unlikely we will see a repeat of the level and duration of heat that we have seen already this summer. In-between these shorter-term heat events we will see cooler and unsettled weather with more in the way of thunderstorms for the south I think.

Since we are likely to get plenty of thunderstorm activity this week I thought I would mention the ATD Lightning Detector. This system shows lightning strikes and currently updates every 5 minutes using data from the Met Office Arrival Time Difference system, which is considered to be the most accurate lightning detection available. Each of those crosses in the image above is a recorded lightning strike over the last 24 hours and its approximate timing. There are also plenty of apps (Blitzortung seems good) that focus specifically on lightning and provide warnings of storms travelling in your direction. I use Netweather.tv as a subscriber and they have access to the ATD system. It's great for tracking storms. Above you can see the last 24 hours of lightning strikes and how the breakdown started across Ireland.

Agronomic Notes

OK, A lot to discuss...

Soil hydrophobicity

So one of the key things we need to focus on this week is utilising / maximising whatever rainfall we get and preventing run-off. One tool in the toolbox is soil surfactants. Now soil surfactant chemistry has come on a long way and there are numerous options to consider on the market but crucially you need a chemistry that effectively neutralises soil hydrophobicity. It's no good just using a penetrant that breaks down water tension because our soils are dry now and hydrophobic. If in doubt, just make up a small amount of soil surfactant in solution, go to a dry area and assess the behaviour of the product solution when applied to the surface. If it beads up on the surface (see above), then it isn't going to do a fab job for you.

I remember this picture from 2018 but I don't remember where it came from, so can't give credit. It neatly highlights what a lot of fairways and outfield look like currently.

Is my grass going to come back ?

In the above pictures (of a fairway and a domestic lawn in the summer of 2018), you can see both dormant (light brown, bleached colour) and darker, black looking grass. The former is likely to regenerate provided the crown integrity is intact. This is the part of the grass plant that differentiates into roots and shoots, I think of it as the heart of the grass plant. If you take some samples of grass on affected areas you aren't sure will degenerate, you can strip back the leaves and look at the base (crown) of the plant.

If it is tan colour like this, It isn't going to regenerate. If it is white, it probably is....

You can also take some cores from affected areas, plant them in a pot of rootzone and water them and keep them inside. You'll soon see the grass plant react if it is alive and this will give you an insight as to how much grass cover you'll have in places this autumn provided we get more rainfall. The grown on cores tip is also useful in disease and vandalism cases and saves a lot of time.

Great recovery

Speaking of cores, the green above was hollow cored and vertidrained 9 days ago and you wouldn't really know it judging by the recovery. You can clearly see new plant in the core holes growing faster than the resident plants because of the increased oxygen content and lack of compaction afforded by the new rootzone (topdressing) material.

The greens weren't overseeded by the way. This is why we need to aerate and why summer aeration provides so much faster recovery than delaying it till later into the autumn when disease pressure is higher and recovery potential a lot longer. You do need a reliable irrigation system though together with good communication and an understanding membership !!!!!!

Higher humidity = higher disease pressure

One advantage of the dry summer and low humidity up until now has been the lack of foliar disease activity. OK, on irrigated areas where you are artificially raising the moisture content of the soil and increasing plant leaf wetness for a short period , that is an exception but aside from this, the disease pressure has been low.

That's not to say there hasn't been disease because I have had plenty of reports of Waitea, Anthracnose and also Plant Parasitic Nematode activity (OK, the latter isn't a disease, but it is a plant pathogen)

When you look at the Smith Kerns Dollar Spot Probability chart below for Milton Keynes, you get some idea of what I'm talking about. Now the way this model works is that it calculates the probability of Dollar Spot using a 5-day average of minimum and maximum air temperature and relative humidity. It also works on the assumption that above 30°C and below 10°C, the pathogen is inactive. That incidentally is why it isn't that good as a Microdochium predictor because Microdochium nivale is active from 0°C and only needs 6 hours of the correct conditions to become an issue.

In the States, they use a probability level of 20% as a guide to applying a preventative fungicide for Dollar Spot. Now of course we don't work that way, Dollar Spot over here and in Ireland tends to be a pathogen of tees, aprons and fairways, rather than greens (but not exclusively I might add) and so we aren't going to be plastering a preventative fungicide on large scale areas. In practice, once the Smith Kerns starts showing 50-60% probability, this is when you could see activity on your site if you have previously seen Dollar Spot. Well you can see from the above graph, we have been nowhere near that over the last 6 weeks because the relative humidity has been so low.

With the arrival of higher humidity this week, I expect to see an increase in disease activity from Dollar Spot, but also some of the more humidity-related diseases like Red Thread and Superficial Fairy Ring.

We have to also remember that the grass plant (Poa I'm talking about) has been relatively dormant of late and will start to grow with the onset of cooler, unsettled conditions. It is at this point that you often see the plant keel over from something like Anthracnose or Take All as the higher growth rate requires more water and nutrient to support it and the plant cannot uptake sufficiently through a damaged root system.

OK, that's me for this week, I hope you all get a piece of the rainfall action, I really do.

All the best.

Mark Hunt