May 14th, 2025
- Mark Hunt
- 14 minutes ago
- 7 min read
Hi All,
Long time, no blog, yes I know, my apologies, but I've been away to North Norfolk chasing Mullet on the sand flats of Thornham and Holkham Beach in some truly beautiful weather, up to Scotland installing some new stations and then down to Bristol to talk at the new GMA Connect event this week, so in short, my Monday's haven't been my own (except while I am fishing that is :)
Whilst in Norfolk I experienced some big spring tides, flooding all of the marshes and making you cast more than an anxious glance behind you to ensure you had a way off the beach. As the tide pushed in, nature and particularly birds went into overdrive, waders, ducks, Egrets and Geese pilling onto the wetlands behind the dunes as their feeding grounds submerged, the air absolutely full of their calls. I watched a Barn Owl opportunistically picking up fleeing rodents early in the evening, no doubt with willing mouths to feed. It was simply beautiful.
Whilst out fishing both away and closer to home I noticed how many more insects and butterflies there are on the wing compared to last year, a drier, warmer spring for insects has been just the tonic compared to last years wet, cool and dull affair.
What isn't a tonic to insects and especially aquatic ones is the effect of insecticides like Imidacloprid and Fipronil, of course. Whilst their use in agriculture is I believe very limited now (I stand to be corrected / informed of course), I was quite amazed to find that these two chemicals make up some of more popular flea and tick controls for dogs. And of course when those dogs are taken for a swim too soon after treatment, guess where the chemical goes ? Look on the net and you'll find plenty of references to elevated levels of these chemicals in water courses (here for example) and the effect on aquatic insects. There is a code of practice here but its one I think many dog owners may be unaware of possibly, so I am simply highlighting the issue. After all, nature needs as much help as it can get and insects are often the bottom of an elaborate food chain. We simply can't afford another DDT-like scenario. Ok, off the soapbox and onto the weather.
One last nature anecdote before I do. I always put water out for wildlife during times like these, utilising an old plant plot tray. I have had everything from birds to mice, hedgehogs and foxes coming into the garden for a drink of late, but the undisputed masters of bathing are definitely Starlings, particularly young ones, they really know how to enjoy themselves.....
Well it has been a tad dry hasn't it ?
As I talked about yesterday at the excellent GMA Connect event down at Bristol City's ground (thanks all for the organisation and attending), the jet stream ran out of puff in the 3rd week of March. Since that date we have had a run of high pressure systems sitting over the U.K, Ireland and the continent and this has been due to a Diffluent Blocking Event, typical of the spring season and shown in the schematic above.
Browsing on the excellent Meteoblue.com today, their animated graphic of wind / temperature (below) shows it up really well I think.....
One of the consequences of this type of blocking system is that the dominant wind direction becomes easterly and that's exactly what we have seen. Up until yesterday, many places have had no rainfall at all in May and many after yesterday remain so.
With a very wet winter preceding this blocking event, aquafers were nicely topped up, so soils were initially resilient, however of late we can see plant drought stress evident both in crops and turf. Spring-sown crops in particular around here in Leicestershire are meagre at best. Warm / hot and windy weather is really ramping up the evapotranspiration rates (E.T) of late with close to 5mm of moisture lost per day (more on that later). Just tonight I read that this spring is heading towards being the driest ever (read it here) and they're already starting to talk about the possibility of water restrictions.
So we are stuck in a 6-week old weather pattern, is there any sign of change I wonder ?
Well looking at the GFS I think there may possibly be so as I put my head above the meteorological parapet. The way I see it is that the Diffluent Blocking pattern is changing to an Omega Blocking pattern and that is significant because it may be more prone to breaking down (in my humble meteorological opinion). Now if we look at Meteoblue's forecast probabilities in their app, they are pretty high (>50%) up until the middle of next week. Fair enough I'd say as any further than that is tricky but if you look at the GFS projection above, that's exactly when there is a potential breakdown to a more unsettled theme. At that point (around 22nd, 23rd May) a cut-off low pressure system forms and it is this that could be the catalyst to change, pulling down cooler and more unsettled weather at the same time as the jet stream meanders southward.
Things that make you go hmmmm.....
Now don't get me wrong a lot can change between now and then weather-wise, but there's maybe, just maybe the first signs of a change underway. What a caveat-laden declaration that is 😂
Agronomic Notes
Lot's to talk about here....let us start with moisture......
So, we all know that we have been in an extended run of dry weather with some locations over 3 weeks since rainfall. I had been thinking turf areas were holding up pretty well until the last week or so when I began to see clear signs of plant stress. The tipping point has been due not so much to the lack of rainfall but the rate at which moisture has been removed from the soil and grass plant by evaporation and transpiration respectively.
A snippet from our monthly soil moisture status report showing SMD (Soil moisture deficit) / SMS (Soil moisture status) from our default Thame location in the U.K shows how the 1st half of May has been characterised by some pretty high daily E.T rates. Thanks as always to Sean Wilson @ The Oxfordshire for allowing me to use this data.
Anything in my books over 4mm per day moisture loss generates plant stress, so we can see why May has already been a challenging month.
When you look at the soil moisture surplus / deficit status plotted from the beginning of the year, you can see we had significant surplus up to the end of February and then the rate of moisture input from rainfall was less per day than the rate of moisture loss by evapotranspiration. By the 3rd week of April we were at parity and since then we have moved into a deficit situation. Now of course this is an overly-simplistic calculation because it is entirely dependent on the soil type and its capacity to retain moisture. For lighter, sandier soils, this capacity is limited and therefore the actual soil moisture deficit is more exaggerated.
The combination of heat and wind strength is what really does the damage.
Typically during the day we start off with low ET values, but as air temperature rises, convection generates increasing wind strength and therefore moisture loss from the soil and grass plant. The 13th of May was one such day with significant wind strength and air temperatures rising to 24°C.
Below is the hourly moisture loss by E.T plotted out against time of day for the above location.
Think about the above in relation to when you hand water and irrigate, tricky eh as we still were experiencing significant moisture loss at 6pm.
May is a YO-YO month.....
Up and down growth...
Above is the minimum and maximum air temperature plotted against daily Growth Potential for the month-to-date. What you can see is that for a part of this time period, the minimum air temperature at night is in the low single figures, even bordering on a ground frost on occasion. Despite the fact that the maximum air temperature was in the teens or even twenties, the cold night temperature is dragging down the daily growth potential to the point where it is similar to February's daily Growth Potential.
So what appears to the layman / woman as great conditions for grass growth, is in fact entirely the opposite. Now this is nothing new, May in my books is always a Yo-Yo month temperature and growth-wise and often we don't see night temperatures stabilise till the end of the month and then we see consistent growth.
One of the reasons we are seeing colder night temperatures has been because of the Diffluent Blocking Event, with colder winds funnelled between the dominant high pressure / low pressure systems off The North Sea from the E and NE typically.
Differential growth
Of course at the same time Poa annua is in the middle of its seedhead flush, it is under elevated levels of plant stress and night temperatures are on occasion, holding back growth. So we have differential growth across a surface between Poa annua and Bentgrass, with Bentgrass loving the dry and bright weather (after all it has a high DLI requirement). so we see Bent broaden its leaf and Poa annua hunker down. All the constituents for an uneven, bobbly surface I am afraid.
During this period, having a high cutting height is hard work and so light topdressings and rolling (often in place of cutting to reduce stress) are the order of the day. Cutting heights are an emotive subject between golfers and greenkeepers. There's always a vocal minority that want faster greens but shaving down your greens longer-term comes at a price. It increases plant stress and requires more consistent inputs, both nutritional and pesticidal.
Research from Rutgers University on Anthracnose for example severity shows a marked increase in the severity of damage once the cutting height is dropped below 3.2mm. Now one thing I do know is that when you have this disease across your greens in August and September, your surfaces are pretty sub-optimal and this lasts for weeks, there is no easy fix, you can't make it 'go away'. So if you go down this road, you have to buy into greater inputs and increased risk of disease and of course it is entirely dependent on grass species composition. I am not wishing to start another debate, we know you can sit at low cutting heights but it comes at a price, that's all. Like most things in life, there is a compromise. Controlling surface organic matter, with good levels of topdressing, a sensible cutting height and rolling can produce great surfaces. Of course as we know, we can tolerate short periods of lowered height, such as during tournaments / events with no problem, it is just about being sensible and seeing the bigger picture.
OK, that's me for this blog, I'll update next Monday as we will know more about how the GFS outlook is progressing and whether or not we will get some rain.
All the best.
Mark Hunt