July 29th, 2025

Hi All,

Well, I for one am certainly enjoying the cooler days and nights that we have had recently and a nice drop of rain to boot as well. Since the middle of July we have also seen the E.T rates back off a little to make irrigation and plant stress a little more manageable. Make no mistake though, we are still in a prolonged drought with a soil moisture deficit higher than I can remember seeing for this time of year and August still to come. Cooler and a bit wetter means more humidity so that comes with its own management challenges in terms of disease activity, never a dull moment for a turf manager eh ?

The reason for the change has been a stronger jet stream which has prevented high pressure systems from dominating as they did in May, June and the first part of July. In addition we have seen a feature known as a cut-off low (COL) which is an area of low pressure detached from the jet stream. The animated GIF courtesy of tropicaltidbits.com above shows how they form, almost like a teardrop detaching from the column of cool air marking the demarcation line of the jet stream. These COL's are hard to forecast in terms of how and when they form and what they do after they have formed. Last September, a COL was responsible for causing significant flooding in Central Europe, Spain and the U.K. That same COL made September our wettest month of the year, previously unheard of I'd say. As an observer what I see when we have a COL in the weather picture is firstly it introduces inaccuracy / unpredictability into the general weather picture and more importantly maybe, it also tends to pull down more cooler, wetter weather rather than allow high pressure to dominate.

Just my gut feeling.

As you may suspect by my focus on COL's, they are in the forecast for the next 7-14 days and have been present actually since we saw the weather change in mid-July. So when you are reading this blog and looking at the animated GIF I post for the forward GFS projection, keep an eye out for those COL's and how they behave.

General Weather Situation - w/c 28th July, 2025

So I begin with a caveat, I think our weather currently is pretty unforecastable past 5 - 7 days because of the elements I have detailed above, but here goes anyway.

This week we have an Atlantic high pressure system trying to push in from the west and butting up against an area of low pressure to the east, in fact just to the east of Denmark. So we will rain, some of it heavy for Denmark this week, with the threat of rain lasting through the week. For Ireland and the U.K, we have this ridge of high pressure trying to assert itself, but elements from that eastern low will allow showers to build and push down across the U.K through the week.

When we have high pressure butting up against low pressure, we often see the wind is squeezed between the two weather systems and tends to take on a northerly orientation. So that means a cooler edge to the temperatures keeping them pinned down to high teens and low twenties for the U.K, Ireland and Denmark and a sunshine and showers sort of forecast for this week. Not the end of the world I'd say. As we approach the weekend, a more consolidated rain front pushes into Ireland on Saturday and that low pressure system sitting off in The North Sea west of Denmark begins to edge back eastwards.

Now for my Danish readers that is significant because we know the sea temperature to the west / south west of Denmark is warmer than the east. This means in my books that low pressure will pick up energy, temperature and more rain before it makes landfall in W.Jutland on Sunday morning pushing eastwards across Denmark through the day. So that could mean some heavy, localised rainfall here. As we go from Saturday through to Sunday, that rain will cross the Irish Sea into Wales and the west coast of the U.K before moving eastwards, so a wet Sunday is potentially on the cards here, whilst Ireland enjoys a dry down day.

Weather Outlook - w/c 4th August, 2025

Well a complicated picture for next week as we see a southerly low pressure sitting off the coast of Ireland on Monday morning, so that would suggest a wet one for the southern part of Ireland and possibly Wales, the south and north west of England. That low pressure will push eastwards bringing the rain to central and northern areas of the U.K, before crossing The North Sea into Denmark on Tuesday. Possibly another very wet day for you guys next Tuesday. As that low moves eastwards, a ridge of high pressure pushes up behind it to settle things down for Ireland and the west of the U.K and from mid-week for Denmark. A northerly airstream follows behind so it'll keep things on the cool side next week, similar I think to this week temperature-wise. That easterly low pressure now forms into a COL, so that's one to keep an eye on. From mid-week onwards things look to settle down but at the end of next week we see a new Atlantic low pressure trying to displace that high pressure ridge. Beyond that it's for La-La Land, so there endeth my take on next week's weather !

Agronomic Notes

Over the last year or so I have been looking into Anthracnose as a disease.

As I have written about before, this disease isn't straight-forward in terms of control.

Firstly, we have limited options at our disposal because one of the most effective products - Azoxystrobin has been around for over 20 years now (geez). Strobilurins are single-site effective, i.e. they impact on one specific area of the fungus and as such the probability of resistance developing for this type of control product is high. The more single applications you make subjecting the fungal pathogen you are trying to control (and others of course), the more likely resistance will develop. In the old days we had multi-site products like Chlorothalonil which were great for mixing with Strobilurins to prevent resistance development. They are long since gone and currently we don't have multi-site options in our armoury. Getting back to Anthracnose, yes we still have labelled control options but the key aspect if you have recurring issues is to target the initial trigger for this disease. That is to say, a trigger event occurs long before you see visible signs of Anthracnose damage and in my mind by the time you see this disease, fungicidal control is pretty ineffective.

So identifying this initial trigger is key and that's where the Anthracnose Severity Index (ASI for short) comes in. The Anthracnose Severity Index is a disease model developed way back by the infamous Karl Danneberger and Joe Vargas. It works on a combination of temperature and leaf wetness duration. With access to both leaf wetness severity and duration, I have taken the original concept of ASI, modified it and applied it to European data.

Now of course other diseases like Leaf Spot, Dollar Spot and the like are also impacted by the same factors as ASI, so if you see a high reading for ASI, you can bet your bottom dollar (pardon the pun), other diseases are at work.

It isn't just about pesticidal control of this disease. As I have talked about before this disease is encouraged by certain agronomic practices / climatic conditions (high plant stress, low plant N, etc) and so if you see a trigger event then it can serve to mark your card that you should have the necessary BMP's identified by Bruce Clarke and his team at Rutgers University in place. (Read all about the disease and those BMP's here)

This summer we have seen high temperatures and high humidity but they haven't occurred everywhere at the same time. So I have graphed out the ASI readings for June and July for some different locations. Now I can only produce this data if I have access to a Davis weather station AND Davis leaf wetness severity / duration data, so if currently that's lacking in some areas, so no Wales, no Irish data I am afraid. The interpretation of ASI data is as follows. Below a reading of 2.0, low risk of activity. Between 2.0-2.5, moderate risk and >2.5, high risk of activity. I have drawn a line at the upper activity threshold. Here's how the data looks for some different locations ;

ASI index - Multiple locations - Summer 2025

So you can see some locations like Bath have had two main activity events so far this summer, whereas Scotland and Denmark have had one, though the timing has been quite different.

And in a way that's the rub with this disease, it is very location-specific so just because you might see some images on social media of Anthracnose or Anthracnose-like symptoms, it doesn't necessarily mean it is coming your way unless you have similar climatic conditions that is.

As mentioned above, activity from an ASI perspective is also likely to be indicative of activity of other turfgrass diseases, no great surprise there as they all require leaf wetness and a certain humidity / temperature combination. So for example on the Danish data, you can see quite a prolonged period of medium (>2.0) - high activity since around the 17th of July, whereas for Bath, they had two higher peaks around the 19th of June and 10th of July.

Once we have an initial trigger event, we will then see symptoms later, sometimes 14 days after this initial trigger, sometimes it takes longer because Anthracnose is a real ticker of a fungus, no point growing quickly when you can just slowly motor along and do a thorough job of killing a grass plant. It grows much, much slower than its racier compatriots like Dollar Spot and Microdochium, so you often see symptoms, then you think it has gone away, only to come in and find more areas affected. What it does share with Dollar Spot is the inability to get recovery in the affected areas, it seems to take a very low time and it also shares a similar period of activity, right in the middle of peak golf.

One to keep an eye out for sure in the coming weeks, especially if you have a history of this pathogen on your site.

OK, that's me for another week, no blog next week as I am off in the camper to chase Mullet and Bass and have some switch off time in the rain (yeah right)

All the best.

Mark Hunt