What a weather week we had last week with a new record high temperature at Heathrow for July at 36.7°C, pipping the previous record recorded at Wisley of 36.5°C, recorded in 2006. I measured 35.5°C here in The Midlands and decided to test my stamina by going for a 4 mile lunchtime run at the hottest point of the day, I don’t think I’ll do that again 🙁 We also measured some extremely high E.T (Evapo-transpiration) levels during that heat, more on that later.
The heat of mid week was followed by some of the most active thunder and lightning storms ever recorded with hail the size of golf balls, torrential rain and over 13,000 lightning strikes recorded from Friday evening through to Saturday morning. As predicted the storms came off the continent as they had done earlier in the week. The lightning archive on Netweather Extra shows the path of the storms in the merged graphic below ;
Sadly I didn’t manage to get a water sample from these storms, but it’s a fair bet that it was loaded with N and you’ll already be noticing the result on your turf areas. It always amazes me how you can irrigate an area during dry spells but the moment we get rain and particularly rain from thunderstorms, they green up. I measured 13.4mm fell here in Market Harborough over a short period.
So what kind of a weather week do we have in store for us this week ?
Well a very different week you may be pleased to hear, as an Atlantic low pressure system will bring cooler and wetter weather to the west and north, whereas the south east of England may just sit in a high pressure bubble. Either way it’ll be pleasantly cooler at least for the early part of the week.
So Monday sees the first of those rain fronts already into the south west of Ireland and pushing across during the day to give some pretty heavy rain across Leinster and south east Munster. The rain will move diagonally (/) north east across to skirt Wales by early afternoon and then push into The Lakes and south west / central Scotland by the evening, so a wet end to the day there. South of a line roughly along the M62, it’ll be a different with hazy cloud and sunshine making it a pleasant day, dry and warm. Winds will be moderate and from the south west, courtesy of that low pressure and it’ll be high teens under that rain in the north and west, but low twenties south of that rain.
Come Tuesday and that rain pushes into Wales and the south west / north west of England overnight and then moves east across the U.K during the day. Ireland and Scotland will continue their wet theme through Tuesday with frequent rain showers and a cooler south west wind. There’s always the chance of missing westerly rain if you’re located in central or eastern England and this could well be the case for Tuesday with a likelihood of that rain fizzling out during Tuesday afternoon. Cooler temperatures for Tuesday, mid to high teens the order of the day and still with that south west wind in situ.
Wednesday continues the unsettled theme for the week albeit with less rain around in general. So we start Wednesday with rain still affecting Ireland, Wales, the west coastline of the U.K and Scotland. Through the morning that rain fizzles out over Ireland in general but will still affect Leinster, Wales, the west coast of England and Scotland. During the morning that rain could shift eastwards to affect the north of England and during the afternoon potentially the east coast pushing down into The Wash area. Behind it it’ll leave a drier picture, brighter in the south where that hazy sunshine will give way to clearer spells of sun. Temperatures will range from mid-high teens under that rain to low twenties in the Costa Del Sol of England. Potentially a little cooler across The Midlands as that wind moves round during the day, through westerly to slightly north-westerly.
For Thursday we have a much drier picture across all of the U.K and Ireland. Later in the morning we will see a rain front tickle the coast of south west Munster, The Dingle Peninsular and that rain will push across Ireland during Thursday. Some of that rain may just reach south west Scotland by late Thursday night, but away from this localised area of rain, it’ll be a lovely sunny summers day, dry and warm with temperature in the low twenties for all and hazy sunshine giving way to brighter spells later in the afternoon.
Closing out the week we have that rain pushing into Scotland, North Wales and northern England overnight, clearing Ireland as it does so. Further south and east, another lovely day with hazy sunshine breaking up to give a warm / hot day, with temperatures pushing right up to the low / mid-twenties again across Central England. Winds will be lighter and from the south, that’s what will cause the heat to start to build again in the south of England. Where you have the rain it’ll be cooler, maybe only mid-teens across Scotland as you pick up a cooler easterly airflow.
The weekend could continue the ‘mixed bag’ sort of weather because the low pressure system is projected to push across the U.K during Saturday and Sunday. That suggests the unsettled, cooler theme will continue for the west and north with rain likely on Saturday. Further south it’s a tricky one to call because it really depends just how far south the influence of that low pressure extends. In the far south east we could see the effects of continental weather again with heat funneling up from the south and giving hot temperatures for Saturday at least, maybe mid to high twenties. It wouldn’t surprise me if we get some more thunderstorms on Saturday night as that hot air meets the cooler, moist air, though none are currently forecast. That heat should dip away on Sunday to a more pleasant low twenties sort of feel for England and potentially drier as well for the north and west.
Looking ahead we don’t have a clearly-defined, settled, weather pattern because we have a low-lying jet stream and another Atlantic low pressure system waiting in the wings. So next week looks like starting off settled and dry with warm temperatures in the south and south-east. Further north and west will become affected by this new Atlantic low pressure system later on Tuesday and that’ll push down to affect all areas of the U.K and Ireland from mid-week onwards so potentially some rain around for the driest areas at the close of the week. To summarise, warm, dry and settled in the south for the early part of the week with unsettled weather pushing into the west and north from Tuesday onwards and pushing south to affect all areas by the close of the week.
Lots to talk about today after last weeks weather 🙂
Firstly – Evapotranspiration
Last week as we know saw unprecedented high temperatures and they were accompanied by some pretty blustery winds and these really ‘broke the mould’ as far as I’m concerned in terms of recorded E.T levels.
Looking at the data from The Oxfordshire for last Wednesday we see that the total moisture loss recorded over the 24 hour period was 10.72mm !, now that’s the highest I’ve known recorded. The weather station was check / calibrated earlier this year so I have no reason to doubt the figure but I’m interested in what other sites recorded, did you also see extremely high E.T figures last Wednesday, if so how high ?
Here’s how the day played out in terms of temperature, wind strength and E.T…
What made Wednesday, July 1st such a brutal day from a moisture loss perspective was a double peak in E.T, with the normal increase in E.T up to 2 p.m, but this was then followed by a second peak as the air temperature increased further from 3 p.m through to 6 p.m and that was unusual.
So we lost 10.72mm from the turf over a 24 hour period.
The perceived wisdom is that in order for a cool season grass species like Perennial Ryegrass or Poa annua to survive you’ll need to replace a minimum of 40% of that moisture loss by rainfall and / or irrigation. So that means for Wednesday alone you’d have needed to apply 4.3mm of water. If you wanted to apply enough moisture to maintain growth, that figure would have to increase to 60% of E.T and 6.4mm. It is however is a very subjective area and there are a lot more variables involved than just how much water you are able to apply that will determine whether the grass plant will survive or not.
Consider the picture below….
Here we have a Poa annua plant (with a new seedhead visible) that has managed to survive last week’s high temperatures and maintain leaf colour. Next to and around it, is a modern Perennial Ryegrass mix, bred for drought tolerance and fineness of leaf and you can see it hasn’t performed as well. So why is this the case, how come Poa has the upper hand when everything you read says it should be one of the first grass plants to check out when the E.T level is high and moisture scarce ? It’s a difficult question to answer and one I can’t immediatley get to the bottom of, but I suspect that the Poa annua plant has the deeper root system in this case. That said, you would think that the Ryegrass would be the deeper-rooted plant and so more likely to maintain moisture status in the plant itself, but this doesn’t seem to be the case.
The other question in my mind is whether the bleached ryegrass will actually survive and regenerate with moisture ?
This image incidentally was taken with a simple Veho Discovery x200 microscope that connects to your P.C / Tablet through a U.S.B port and is an invaluable tool (I find) when you have this kind of turf-related issue.
So provided there is sufficient moisture, nutrient and an intact root system (all three are linked of course) to sustain this new growth, it should regenerate. Of course the Poa plant sitting next to it will have set its seed by then so I’d expect to see an increase in Poa annua on this area of turf after heat stress.
Makes you kind of wonder then if you still believe the theory that stressing your turf out will favour grass species other than Poa annua doesn’t it ?
Talking of other plant species that’ll show an increase in population density during a drought we can expect to see more moss and algae on thin areas of the sward where grass cover has been lost. This is because moss can survive dessication better than grass during high temperatures / low moisture. The algae is normally a result of grass density loss and colonisation of decaying plant material.
Before I leave drought and drought survival, one of the key factors that will help achieve plant survival during periods of weather like this is your root system and that comes down to another set of variables, not least organic matter content, compaction, etc.
In other words all the things we do when we aerate to try and control organic matter, relieve compaction and increase the air-filled porosity of the soil we are maintaining (to encourage better rooting). All this work comes home to roost when we go through periods of weather like this. So if after last week you’re looking at a pretty healthy sward with minimal grass loss and good coverage, use that to reinforce with your management why it’s so important to do what you do aeration-wise at other times of year.
Looking back at June….
June was a so-so month from a growth perspective as the GDD information above shows and although we had reasonable temperatures through the second part of the month, it wasn’t temperature that was growth-limiting in June, it was rainfall.
The chart below shows growth potential and rainfall for a site in York (Cheers Adrian) and you can clearly see the up and down nature of growth (normally it’s more consistent once we reach the end of May) and the large gaps between periods of rainfall. (particularly after the middle of the month)
Nutrition, aeration and disease activity going forward…
With a more unsettled picture for the weather this week and potentially next, we can use the lower temperatures, lower E.T and higher potential for rainfall (except the south / south east) to gently bring the grass plant back on track. This should be done with a light / moderate amount of nutrition to increase the grass plant’s nutrient status and in conjunction with biostimulant use to maintain plant health, the two go hand in hand at this time of year. If your grass is stressed then drop your PGR rate or cut it out altogether until you have achieved recovery. Light aeration (Solid tining, Sarel rolling, etc) will help to stimulate new root development and vent the soil. I’d be careful with verticutting or scarifying if the plant is under stress and follow up aeration with topdressing if practically feasible.
Disease-wise, the high temperatures and rainfall will undoubtedly trigger off lots of Fairy Ring activity, along with Waitea Patch (they look similar sometimes) and these will require management in the usual ways. Speaking of disease I’d be using this week to get my preventative fungicide down for Anthracnose if you haven’t already done so. With last week’s high temperatures I think we’d have seen Anthracnose spore germination in the soil. It doesn’t necessarily follow that you’ll see Anthracnose this year but fore-armed is fore-warned. This is really a priority on turf areas that suffered high levels of Anthracnose activity in the summer / autumn of 2014.
Ok that’s all for now, enjoy the cooler temperatures and particularly the cooler nights, it should mean getting some shuteye is easier for one and all 🙂
All the best.