June 16th, 2025

Hi All,

Ah, the 'Glorious 16th' as it once was known, the date in the year when the fishing season close season comes to an end on British rivers. As a young lad, the countdown to this date was met with growing excitement, now it passes with a wry smile. Not that there's a whole bunch of water in those rivers at the moment mind with the dry spell continuing. Yes, we saw rain at the end of last week, up the west side of the country and spectacularly up the east on Friday night accompanied by thunderstorms that moved across The Channel from Northern France. That leaves the middle of England drier than the east with a typical annual rainfall of 180mm y.t.d compared to last year's figure of 430mm at the same date. Some difference. I cycled across one of my local brooks at the weekend and it was barely flowing, this with 2 1/2 months of summer still to come.

Image left from lightning.org

You can see the track of the storm across Kent and Essex on the left and the resulting rainfall in the middle image - 57mm of rain rising to a rain rate of 256mm per hour (just over 10" an hour rain rate). No small wonder there was flooding. A day later, we were in bright sunshine and strong winds and that really ramped up the E.T pushing up to 4.6mm on some of the locations I have measured. Windy and warm = high E.T, that we know.

Courtesy of tropicaltidbits.com

This week's weather for the U.K and Ireland is set fair as predicted at the start of last week. A warm and increasingly humid air peak will push up from Africa and that'll result in an increasing temperature and humidity trend as we move through the week, potentially culminating in a breakdown over the coming weekend. This heat plume will push temperatures up into the high twenties / low thirties by Friday, our warmest weather of the year so far. Further north across Northern Ireland and NW Scotland, it'll be cooler with the risk of showers across western-facing coasts as a northerly low influences the weather. As you can see for Denmark, the heat is east of the country so here we will see more pleasant temperatures sitting in the low twenties. The heat and humidity combination last week and potentially at the end of this week spell problems from a disease perspective, more on that later.

Courtesy of tropicaltidbits.com

Weather Outlook

Looking beyond this week is tricky because when heat plumes break down, they can simply reform again or a more complex weather picture can take over so it's a tricky one to predict and with a low probability attached.

As it stands currently, the GFS projection is pointing to a low pressure system pushing across Ireland and the U.K on Sunday bringing a cooler and more unsettled theme to the weather for the start of next week. So we look to start cooler, fresher with some showers around next Monday, with a prevailing north westerly wind taking the temperatures I'd say 10°C cooler than it will be at the end of this week. This cooler, unsettled period of weather looks to hold through to mid-week when we will see high pressure exert itself again and the weather settle down to dry and warm. The same pattern appears to hold for Denmark, warm and dry this week with temperatures increasing at the weekend and then potentially cooler, more unsettled weather with rain from the beginning of next week lasting through the week and also accompanied by cooler, northerly winds. I repeat though the caveat accompanied to this forecast because high temperature breakdowns are unpredictable.

Agronomic Notes

Anthracnose

Last week, I mentioned that the weekend past might meet the conditions required for Anthracnose fungal development, that of high temperature and leaf wetness and I can confirm they did.

I have been working on using an Anthracnose disease model within our reporting software (Prodata Reports) that takes data from the Davis weather station and crucially an additional leaf wetness sensor (pictured above) and converts it into a disease score.

Like most models it provides normal, moderate and high risk thresholds and on Saturday, at many locations, it recorded moderate and high risk readings. The key to the model is the leaf wetness data because Anthracnose as a fungus needs high temperature for spore germination but this must be followed by a prolonged period of plant leaf wetness which allows the developing fungus to grow over a grass plant leaf and then penetrate the epidermis in what is known as the Biotrophic phase of this disease.

The Biotrophic phase is where the fungus sits within the plant itself and is undetected by the plant, there are no apparent symptoms. Controlling this fungus relies on applying a control product in close association with a trigger event. In my experience I'd say there is a 10-14 day window following on from a trigger event, but this is just my gut feeling, as far as I know, it has never been confirmed in research. The reason why a control has to be applied is because the fungus then moves from a Biotrophic state to a Necrotrophic state, damaging plant cells and revealing the symptoms we all know for this disease, whether it be as foliar blight or basal rot. In my experience at this time of year, it is normally as foliar blight but later it develops at the base of the plant with the familiar blackening at the crown. By the time you see these symptoms I feel chemical control is pretty ineffective, potentially ring-fencing existing outbreaks but doing very little to change the current infection status.

It is worth pointing out that not ever golf course / bowling green suffers from this disease and in many cases applying good best management practices is enough to prevent it being an issue. In other cases, Anthracnose is a perennially-occurring issue and a control (applied at the correct time) is necessary to break the cycle. I expect another signal event this coming weekend and therefore we can expect to see symptoms of this disease in early July at my best guess.

Last weekend we also saw the Smith Kerns Dollar Spot Probability Model nudge into the low 20's meaning that the threat of Dollar Spot disease is increasing. Again I feel that the weather forecast for this coming week / weekend will push this score up further, so one to keep an eye on if you are maintaining a course where this disease is problematic.

High temperatures as we will experience at some locations this week will push the grass plant past its comfort zone, particularly for Poa annua, so the trick here is to keep nitrogen applications on a 'spoon feed' level and input biostimulants (typically seaweed, humic and amino acid-based products) to mitigate plant stress. Pigments and PGR's are also extremely useful in conditioning the grass plant prior to stress periods. At high temperatures, photosynthetic efficiency declines, whilst respiration increases, so the plant's ability to make energy decreases just at the time it requires more energy to maintain its moisture / temperature status. This is why pushing plant growth at such a time with nitrogen is not a good idea because you are forcing the plant to grow and therefore consume / utilise its food reserves when it cannot produce them as efficiently. On the other side of the coin, you don't want to produce a plant that is at a low N status (foliar tissue level < 3.5%) because it will be fair game for both of the plant pathogens I have already highlighted.

That is the line you must tread and it is a tricky one, all the best with that.

Mark Hunt