September 22nd, 2025

Hi All,

Quite a shock to the system yesterday morning when I checked the temperature. After a run of nights when the temperature didn't dip below 15°C, yesterday we saw parts of the U.K experience a ground frost, the same today. The reason ?

A change in our wind direction, swinging round to the north and high pressure building. High pressure tends to be associated with clear skies which allow heat to escape to the atmosphere. So a drier interlude this week after the heavy rain (for some) of the weekend, with areas of Yorkshire picking up 50mm in a day. Hopefully that'll help the depleted reservoir levels up there.

It shouldn't come as a surprise really, because today marks the autumn equinox, when the sun is directly above the equator and so night and day length are equal

Clear skies mean more autumnal sunshine and beautiful colours from the leaves changing hue. Last year, I took this picture of an avenue of Oak trees near Lyndon, Rutland.

One of my favourite parts of a weekly walk I do with my partner. I call it 'Acorn Alley' because currently when the wind blows, you get bombarded with falling Acorns and there are plenty this year and they are heavy. (Cue the Health and Safety, Cotton Wool brigade, putting up a sign warning of 'Danger of falling Acorns' )🙄

I love the change in colours on this part of my walk, the fact that I always hear Woodpeckers and Nuthatch as I walk through the avenue of trees, sometimes a Raven, often Kites and if you stop and be quiet, occasionally a Tree Creeper. It's my favourite for this reason and as importantly, I know I am close to a warming bowl of Soup, a nice Flat White and maybe a shared Kanelsnegle (Cinnamon Bun) at Picks Barn Cafe, Lyndon.

At the weekend I took my camper over to Norfolk in a futile search for Mullet and Bass before hanging up my saltwater gear till next year. The winds of last week had coloured up the sea for at least a mile out, so nothing was doing. My compensation was the late afternoon light over the salt marshes as I walked. Watching the Geese come in across the windmill at Cley, the haunting cry of the Curlew and a Marsh Harrier hunting, I'll take that. 'Nature is a language, can't you read?' sang The Smiths, plenty can but plenty can't and especially not the KWD brigade as I have named them. (the 'D' stands for dogs)

For turf managers, autumn brings its own challenges of course, last week's humid night time temperatures brought disease activity and heavy dews to contend with. As the ground wets up again, worm activity will become an issue and of course leaves, lots of fallen leaves. Every season has its own set of challenges for sure.

Onto the weather....Well it is still 'variable' and a challenge to forecast for sure.

Image and above animated GIF courtesy of tropicaltidbits.com

One of the reasons I think it is tricky to forecast is the creation of a cut-off lo pressure system during the early part of this week. These meteorological phenomenon are very hard to forecast in terms of where they move and the rainfall associated with them. Last year, a cut-off low pressure looped over the southern half of the U.K and brought 166mm of rainfall to Leicestershire, making September 2024, our wettest month of the year.

Currently the outlook for this week is for high pressure to build and maintain the run of lovely autumn mornings, heavy dews, cold mind with them and daytime temperatures rising to the mid-teens. Those northerly / north easterly winds will be a continuing feature and that's why we have cold / cooler temperatures than of late. The cold nights that have brought a ground frost to many areas away from the still warm, concrete of the towns and cities will gradually fade as night time temperatures pick up later in the week.

For Ireland, the wind direction will swing round on Tuesday so it'll usher in some slightly warmer weather than we will enjoy across the U.K, warmer nights for sure. Denmark looks very similar to the U.K, dry and settled weather, bright and sunny during the day, cooler at night but still into double figures later in the week. Day time temperatures will drop back from their early twenties peak of last week.

Later on in the week, towards the weekend, this cut-off low moves westwards (against the 'normal' line of movement of weather systems) and joins up with an Atlantic low pressure system. One to watch because its path takes it across the warm seas of The Bay of Biscay, so there's potential for it to intensify rainfall-wise and possibly bring some heavy rain for the start of next week for the south of Ireland and the U.K. It is then projected to move across The North Sea towards Denmark.

Plenty of time for this outlook to change mind and with a cut-off low in the weather picture, I am sure it will as it brings with it an air of unpredictability. Keep an eye on your forecast as we approach the weekend.

Smith Kerns comparison - September 2025 vs. 2024 Thame, U.K - Prodata Reports Software

Agronomic Notes

Last September, we saw two peaks of extremely high Dollar Spot and also Microdochium disease pressure. It was a much more humid scenario in 2024 than it is currently, but last week we saw some very humid weather and very warm overnight temperatures accompanied by heavy dew, so the threat is there.

Overnight leaf wetness report - Prodata Reports - Luton

Overnight leaf wetness report - Prodata Reports - Copenhagen

In the recent past, October used to mark the beginning of our autumnal disease period, now it starts earlier with of course Dollar Spot in the ascendency. With the lengthening nights and cooling temperatures, dew becomes more of an issue as we can see from the two examples above from our Prodata Reports software. The areas I have highlighted feature long periods (over 10 hours in some cases) of high leaf wetness, combined with high humidity and high overnight temperatures.

The Leaf Wetness Mean column is a score out of 15, with a reading of 0 representing no leaf wetness, 8 indicative of dew formation and > 12, heavy dew formation.

So when you see a reading for the Copenhagen location on the 21st September showing 12.8, it marks a heavy dew and 692 minutes, over 11 hours of prolonged leaf wetness. Then look at the mean overnight temperature, 17.2°C, that is optimum for Microdochium nivale and (depending on which model you subscribe to) well into good growing conditions for Clarireedia homeocarpa (Dollar Spot).

We can see a similar peak for the Luton location occurring on the 19th and 20th September with prolonged leaf wetness (> 12 hours), combined with high overnight humidity and temperature.

So if you saw some activity last week, you can see why is was very likely to occur.

From a turf management perspective there are a number of 'choices' that could be made here, pesticidal or non-pesticidal. One of my favourites is dew control, a surfactant designed to reduce water tension on the leaf surface and thereby reduce dew formation and leaf wetness. Now normally we think of using these products in the winter, when growth levels are lower and so you get good longevity from each application. Using them at this time of year brings the familiar concern of 'it doesn't last very long does it'. Well this is true but then when you look at the high pressure peaks of disease that bring damage to your sward, neither do they.

The damage though that these disease do to the surface does last and it may take a long while to grow out if you have say Fescue as your dominant turf species or Creeping bentgrass.

So what price protecting your turf with a dew dispersal to manage these peaks of activity ?

Now during September, growth is still usually good, last week we had almost optimum Growth Potential in both of the locations I featured above, so theoretically and certainly in the case of Microdochium, you'd probably grow out the disease as fast as it attacked the plant. You see that familiar copper blotching where the disease is active but doesn't extend down into the crown of the plant. Dollar Spot though I am not so sure because the evidence is that this pathogen grows faster than the grass can out-grow it even in late summer and early autumn. So even at high daily Growth Potential values, we still see significant damage to the grass sward with Dollar Spot compared to Microdochium nivale. As the daily Growth Potential declines in October, we begin to see more damage to the crown on the plant from Microdochium and Dollar Spot.

If you look at this from a G.P perspective, it is understandable because our average G.P for September is typically up around 0.85-0.90 in England, Wales and Ireland, but only 0.6 for Scotland and Denmark typically (though higher for the latter this year I predict).

So the potential for Microdochium and Dollar Spot damage is higher, earlier, in cooler climates. Once we get to October, the average daily G.P figure drops in England, Wales and Ireland is between 0.5-0.6 and then we start to see more turf damage as the grass plant is growing more slowly and the disease as aggressively. (remembering that Microdochium as a fungus starts growing at 0°C). Of course this potential for growth is purely based on temperature and doesn't take into account the things we do to slow growth, like using a PGR (not in Denmark of course as there it is unavailable now, a calculated choice made in gaining the fungicide, Signum and losing the growth regulator, Primo Maxx).

So, we have to make a judgement call sometimes when it comes to dew control and its usage. Sure your longevity is compromised when the turf is actively growing but if 5-7 days of reduced plant leaf wetness is the price you pay for a significant reduction in say Dollar Spot damage on greens (for which you know the odds will only increase against you growing it out going into winter), then I think its worth paying that price.

Remember also that a dew control product tends to produce a drier leaf even when you start to see dew forming again. What I mean by that is as the products efficacy declines, it is still giving you a drier leaf than you would have without its usage with dew forming for a shorter duration.

An interesting debate for sure and I would just make the point I am not involved with dew surfactants and their efficacy anymore, so my argument is purely agronomic rather than commercial.

OK, that is me for another week, let's see how that cut-off low behaves as we approach the weekend....

All the best.

Mark Hunt