June 9th, 2025

Hi All,

Well most of us have had a nice drop of rain over the last 7-10 days, breaking the cycle of long-term drought that commenced at the end of March. The rain and cooler temperatures has also given us some respite from the high moisture loss by evapotranspiration that we have experienced recently. Let's not kid ourselves though, we are just at the start of meteorological summer (June, July and August) and a few days of rain isn't going to revert the long-term decline in soil moisture status that we have seen this year.

Soil moisture surplus / deficit in mm - 2025 - Milton Keynes

As you can see from the graph above, we hit a neutral soil moisture status at the beginning of May and although this is a simplistic model (because it is entirely dependent on the ability of the soil type to retain moisture), it does tally with my experience that turf started to show stress at that time of year. From early May to the end of the month, we saw a steep downward trend in soil moisture status before it picked up slightly at the end of May / beginning of June as rain arrived. Despite this brief respite, we are still at -71.7 mm for the year and that's at the beginning of summer. So this one is potentially going to be a hard graft I think from a water perspective.

Now I make that statement with obviously no notion of what summer 2025 will bring from a weather forecast perspective and what's more I don't believe anyone else has a notion either. I have said it before but I feel long-term forecasting (beyond 10-14 days) is something for La-La Land. What is clear though is that this week we will see temperatures rise back up again and with it humidity. Those two factors together pose a disease risk from a Dollar Spot activity and potential Anthracnose trigger event perspective.

Temperature and humidity at this time of year spell thunder and lightning and that's a nice coincidence because when I was in France, I was chatting to the couple on the next table, Michael and Romana, who I knew well from past holidays. We were talking about the weather (no surprise there) and the threat of 'L'Orage' (thunder and lightning) that day. Michael ventured a really good website where you can see real-time lightning strikes and the thunder radiating out from the strike. If you set the sound, it clicks every time there's a lightning strike. It is called LightningMaps.org and here's a screenshot from the website.

Lightning data by Blitzortung.org, map data from Google Maps

It may come in handy this week looking at the forecast !

General Weather Situation

So this week we will see a mixed picture of weather. Mixed because we will pick up some serious temperature but with a low pressure system close by, there's a risk of some pretty serious thunderstorms and elevated humidity as well. That said I think the real heatwave could potentially arrive next week with a hot air plume projected to push up from Africa.

So putting some detail on it, Mondays sees a rain front pushing over the north of Ireland, Scotland and the north of England. This rain front will push southwards but fizzle it as it does so. So south of this it'll be a pleasant day with temperatures up on the last few days when it has felt pretty chilly. Overnight that rain front will cross The North Sea and push into Denmark, so more rain for you guys. Tuesday sees a pretty dry day for the U.K & Ireland, but a very wet one for Denmark.

From Wednesday, the temperature really ramps up from high teens at the beginning of the week to mid-twenties by mid-week. A nearby low pressure out in The Atlantic will feed in showers across Ireland during the second part of the day. By Thursday, this rain will have moved across The Irish Sea into The South West and later central England. It may also just touch the east coast of Ireland / Wicklow / Meath sort of area as well. This rain accompanied by rising temperature will likely trigger some fruity thunderstorms, so that website above may come in handy. During Thursday morning, that heavy rain will cross the south coast of England and vector northwards. Again this could be accompanied by some thunderstorms and again mid-twenties temperatures. It'll feel very humid. This rain will then push into northern England and eventually Scotland. Some of the rainfall associated with this front will be localised and very heavy with flooding. Another feature of Thursday will be the elevated temperature pushing up towards 25°C. I haven't mentioned Denmark because this rainfall will be U.K / Ireland-localised and for you it'll be calmer and more settled with temperatures beginning a gentle rise into the high teens initially, but by Sunday it could be mid-twenties for Copenhagen.

Through Friday we will continue to see more showers across Ireland and the U.K and the temperature continuing to rise towards the high twenties. This combination of increased temperatures and rainfall / moisture will provide elevated humidity and more thunderstorms. Again, some of the rainfall could be very heavy and localised. Still some showers around on Saturday, particularly across Ireland and the west of the U.K, drier across the east with temperature dropping back a little on Saturday before falling significantly on Sunday as the wind turns round to the north west. Later on Sunday we will see rain cross the north of Ireland into Scotland. Overnight this rain will push across Denmark.

So a very mixed week of weather, rising temperatures, humidity with some very heavy, localised downpours.

Now next week looks interesting as a hot air plume is projected to build from Africa and push up across southern Europe and into the U.K & Ireland. This heat will begin to increase on Tuesday and then stay in situ all week. Now to the east across Scandinavia, it won't quite be as warm, but temperature will build again towards the end of the week and it'll become drier.

Agronomic Notes

So as suggested above, I think this week will represent significant disease pressure because up until recently we have had dry, warm conditions but accompanied by dry air (low humidity).

That will change this week with higher temperatures and high humidity, a potentially negative combination when it comes to disease.

The mix of diseases that comes with this combination are quite different from other times of the year and 4 of them are shown above.

Bottom left is Waitea Patch, a disease that loves a wet surface and also manifests itself like Superficial Fairy Ring. So if you have some heavy downpours and high temperatures and see yellow patches everywhere, it is likely to be Waitea and / or Superficial Fairy Ring. The two can look very similar but if it is Fairy Ring (top left), you'll tend to see a depressed patch when you push on the surface, accompanied by a musty smell from a core. Waitea has none of this. Fairy Rings and Waitea patch don't tend to take out turf unless the former is accompanied by soil hydrophobicity (shown below), they are merely aesthetically displeasing most of the time. That said, a bad outbreak of Fairy Rings / Waitea isn't what you want if you have an event because it will draw attention for sure. ("What are all of those rings" type comment ???)

The standard treatment is a drench of fungicides like Azoxystrobin, tank-mixed with a soil surfactant (an approved tank mix obviously) and for deeper hydrophobicity, localised tining to aid penetration to the area of activity.

By far the most aggressive of our summer diseases is now Dollar Spot (top right in case you don't know what it looks like !) with a massive increase in geographical area over the last 10 years, marching north with our changing climate. I believe the warm air plumes (an example for this coming weekend is shown above) that we have seen as a feature of our weather are the driver behind this disease because they push warm, humid air further and further north and that's exactly what this disease likes. Humidity, plant leaf wetness and high overnight temperatures are the agronomic drivers for Dollar Spot and we will have all 3 in spades from mid-week onwards, so be aware.

There's plenty of advice out there on controlling this disease from a pesticidal and non-pesticidal perspective, that isn't my bag anymore, but for what it's worth, keeping the leaf dry overnight and hardening it with an iron, manganese and zinc spray worked very well for me back in the day. Remember also that a weak plant from an N status perspective is fair game for Dollar Spot (and Anthracnose for that matter)

For the pitch guys (not exclusively). Grey Leaf Spot is another disease that loves the combination of high temperatures, high humidity and a wet plant leaf and whilst I don't have any current reports, I do think the weather combination in the forecast is conducive to this disease. Again one to keep an eye on.

Although I didn't add it to my picture, Anthracnose or more specifically a trigger for the commencement of Anthracnose fungal development is also likely this coming week with the necessary combination of high temperature AND plant leaf wetness. This disease is a slow burner going through an initial plant leaf entry phase before becoming pathogenic. Controlling it after the trigger event is key to preventing a later incidence in August and September. Like Dollar Spot, Anthracnose is one of our worst diseases precisely because it occurs right in the sweet spot of the playing season (and is therefore front and centre in the golfer's eyes) and it takes a long time for turf to recover.

Now you may be in the position of not usually seeing any of these diseases on the turf you manage, in which case consider yourself extremely fortunate.

OK, that's it for another week for me, it will be interesting to see if that heat plume signature continues to develop on the GFS forecast for next week or declines. My money is on the former.

All the best.

Mark Hunt