It’s been another week of extremes weather-wise with the highest daily temperature of the year last Tuesday / Wednesday for some and then on Saturday night we had a deluge here in Market Harborough with 25mm falling in 30 minutes causing flash flooding and accompanied by some really active lightning. We had so much rain it formed rapids running over the speed humps in the road, brill and the only positive thing I’ll ever say about them
Not everybody got these temperatures or the rainfall for that matter, but if you did, isn’t it amazing how rainfall greens up grass and plants so much more effectively than irrigation water ? It never ceases to amaze me that one….I took a sample in the middle of the thunderstorm so we’ll see how much nitrogen there was in the rain, I think it might have been significant
What has also been noticeable is the cooler night time temperatures since the end of last week and I could almost feel the first chill of autumn in the air on Saturday night, kind of musty and cool, nice though
So are we in for another week of extremes or is the weather settling down as we approach what is traditionally a quiet weather month (and busy golf month fixtures-wise) in September ?
General Weather Situation
So we start Tuesday with high pressure sitting over the south half of the U.K and with some weather fronts trying to push in from the North West Atlantic. So for most of the day we are looking at fine, dry, bright and sunny with warm temperatures building from the off after what was a slightly chilly night. I’d expect mid to even high twenties in the south of England today and low twenties further west and north across Ireland and Scotland. So a settled day with light winds for most, though breezier over Ireland heralding the arrival of a rain front into Kerry and Connacht early this evening. This rain will push across Ireland overnight clearing by dawn on Wednesday. A cool night with temperatures in the low teens.
So Wednesday morning sees this rain band clearing Ireland and stil marching eastwards into western and central Scotland in time for sunrise and then later in the morning affecting north west England, West Wales and the south west of England. By late morning it appears to fizzle out leaving just a band of thicker cloud over the middle of the country. The rain will continue to affect Scotland though, mainly the north and west during the afternoon on Wednesday though this will slowly fizzle out through the late afternoon / evening from central areas of Scotland. Further south we end the day bright and sunny with pleasant warm temperatures with maybe more in the way of cloud across the north and east of England. The wind will still be south westerly but moderate in strength as a low pressure system tries to push in from The Atlantic. I’d expect low twenties for England and mid to high teens for Scotland and Ireland, likely lower under that rain for Scotland.
For Thursday we have another largely dry day although low pressure is trying to influence the weather so breezier and with more cloud cover for most and some rain showers from the off for north west Scotland. So we’ll start off with more in the way of cloud cover but this will burn off over Central England but remain over Ireland and Scotland for much of the day. As we close out Thursday we see the first of those Atlantic low pressure fronts push into north west Scotland bringing rain. Similar temperatures to Wednesday I’d expect with mid to high teens under the cloud cover and low twenties in the sunshine.
Onto Friday then (I do like these 4 day weeks they really fly by !) and a slightly tricky weather picture is on the cards, largely dictated by how far south the low pressure system sinks. This uncertainty in the weather will reflect in how much rain you do or don’t get at the weekend and I expect the outlook to change during the week so keep an eye on it. So that overnight rain for Scotland has moved to cover all but the far north leaving a dry Black Isle and Moray Firth. In addition a weaker rain front has pushed into the west of Ireland to bring thick cloud and light rain for much of the country. By dawn this rain is across Ireland, patchy in places though and is slowly moving south from Scotland and decreasing in intensity as it does so. By late morning expect it into North Wales and north west England and from there it’ll slowly move southwards into northern England, west and eventually South Wales and the south west by close of play Friday. South and east of this advancing rain expect a warm, dry, but cloudier day with temperatures up in the low twenties again with a light to moderate south west wind.
Onto the weekend and this one is really open to change depending on the behaviour of that low pressure system…At this stage Saturday looks like being a cooler day with cloud cover and frequent showers across the west of Ireland, north west of Scotland and England. Some of these showers may push further south and east into The Midlands during the early afternoon. Later in the day a heavier band of rain pushes over Ireland into the west coast of the U.K and Wales / south west of England. A windier and cooler day definitely with a strong to moderate westerly in place. Sunday looks a better day for the British MotGP at Silverstone with breaks in the cloud and less in the way of rain around although overnight from Saturday there’s likely to be a heavy band of rain with thunder possibly pushing across the England clearing during the morning. Thereafter it will be drier and brighter but remaining slightly cooler than the previous week. As I said earlier, lots of uncertainty here about this rain so best to keep a watching brief I’d say and act accordingly.
After a pleasant week and a mixed weekend (possibly) we have high pressure likely to make an appearance from Monday next week pushing up from the south so Monday and Tuesday look to be warm, possibly hot in the south of England particularly. It cools down a shade from Wednesday but looks set fine and dandy the whole week for all of the U.K and Ireland. Now I’ll add a caviat here and that’s Hurricane Gaston, the first of the Atlantic storms and this one currently is looking like it’ll miss us by a long shot. We’ll see though.
Now I appreciate in some areas you’ve had plenty of rain and not a lot of sunshine during August but since I don’t have data for those areas I’ll comment on what I do have data for and that’s the central part of the U.K. (Thanks Sean)
So for some August has been a quite brutal month E.T-wise with significant loss of moisture from the turf surface, some very high air temperatures and sporadic rainfall.
So we start off looking at growth potential and air temperature to see ‘when and if’ the grass plant went under stress ?
Let us just remind ourselves about Growth Potential with respect to plant stress. The principle of the model is based on a prediction of optimum growing conditions for a grass plant with 0 reflecting no growth and 1.0 reflecting optimum growth. If the air temperature gets too hot for grass growth then the model formula takes this into account and you see a drop in the Growth Potential coinciding with high air temperature.
Looking at the above graph we can indeed see a dip in G.P on the 24th and 25th of August at this site so it means that the Poa plant went under stress during this period due to a combination of very high, day time, air temperatures (around 30°C) and high, night time, air temperatures as well (around 20°C).
If we look at the moisture status over the same period we can see that not only was high air temperature coming into play, but E.T was an issue as well…
On those two days the grass plant experienced a combined E.T of 14.2mm, so the rootzone lost 14.2mm of water according to the weather station. We know that replacing 100% of E.T results in gross over-watering, but even if you were replacing 50% of that, you’d have needed to apply 7.1mm just to keep the plant healthy. That is alot of moisture, equivalent to applying 3,550L across 500m2 of golf green or 71,000L across a hectare of turf.
On this site, the moisture deficit across the month of August to date was 105.2mm so assuming 50% replacement we’d have needed to apply 52.6mm of moisture which is roughly 500,000L of water just to keep things ticking ! Like I say a pretty brutal month E.T-wise.
That’s not a lot of plant stress is it ?
If you look at it, two days of high plant stress in August wouldn’t appear to be much, particularly when you consider other areas of the world like the U.S or Australia where they experience weeks and sometimes months of this type of weather…
But in essence it is enough to upset the applecart on primarily Poa greens if we have sub-optimum rooting.
Now this may be because of a physical issue like too much surface fibre for example in the top 20mm or as we discussed last week it may be because of a root pathogen like Take All, Anthracnose or Plant Parasitic Nematodes compromising the efficacy of the roots…
So here’s the two scenarios ;
First off a plant under moisture and E.T stress….
Syringing is a real help during high E.T days..
When a grass plant closes its stomatal pores it incurs a problem and this primarily revolves around over-heating. This is because It uses water loss from these same stomatal pores to cool itself during hot weather, much like we do when you walk out of the shower in the buff and feel the cooling effect of evaporation on your skin as heat energy is removed from your body to drive this process. So when the grass plant closes its stomatal pores it begins to heat up and that’s why applying a light syringe to the leaves during hot days can really help, not by reducing the moisture deficit but by cooling the plants leaves…
It’s worth also mentioning that the regulation of the stomatal pores is carried out by so called ‘Guard Cells’ that change shape according to their cell turgor (internal pressure) and they effectively create an opening called the stomatal pore. Anything involving cell turgor requires water so running the plant very dry isn’t a good idea for that reason. These guard cells achieve this change in shape by regulating their internal pressure using ion transport and two of the ions that are involved with this process are potassium and calcium. And to me that’s why it’s a good idea to provide a balanced nutrient input over the summer. Here’s a complex image I lifted off Wikipedia to illustrate the functioning of Guard Cells…
If roots are sub-optimal during periods of high stress then we are into a whole new ball game…
So the plant needs to take up moisture to replace that lost through E.T but can’t because its root system is damaged and / or sub-optimal (depth-wise) so we have the scenario detailed above…
And this then leads to this type of turf symptom on the surface…
So hopefully I’ve illustrated that only a short period of plant stress is enough to bring with it a whole bundle of joy (not) in terms of plant symptoms and loss of sward integrity. I could go on to talk about what you need to do to avoid this or to get these situations back but it’s getting close to Midday and Tempus Fugit my friends
Selective Herbicide Usage
If it’s not too hot where you are the coming weeks offer an ideal opportunity to apply a selective to summer-germinating weeds that have sprung up all over the place in weakened areas of grass cover. If soil moisture levels are good, knocking those weeds back now and encouraging new grass growth to out-compete them is a worthwhile process in my mind…
All the best for the coming week…