December 11th, 2023

Hi All,

December 2023 has undoubtably started wet with 8 out of the first 10 days featuring rainfall, some of it heavy, as Atlantic low after Atlantic low has pushed in from the west. With accompanying low light levels and E.T, it makes turf maintenance in such a run of weather a tricky and let's face it tough affair, both mentally and physically.

Against this challenging backdrop I am happy to report that we have a break coming from the wet and windy weather dynamic that has characterised the majority of November and December. A ridge of high pressure is projected to push up from the south from mid-week and this will provide welcome relief from the seemingly never-ending run of heavy rain.

Out walking yesterday afternoon, the gloomy skyscape parted to reveal blue sky and a setting sun and I thought that kind of sums up the above. Sodden fields in the foreground and the appearance of sun behind it.

Now the appearance of high pressure at this time of year isn't totally without concern because it is possible that it may bring with it some higher disease pressure than we have seen of late, more on that later.

Speaking of disease pressure, I have had a number of reports that the period last week following the hard frosts coincided with a spike in activity. I discussed this via social media with some superintendents over the weekend. It isn't the first time I have noted this and I wonder if the actual mechanics of the freeze / thaw cycle affects the epidermis of the grass plant and makes it more conducive for penetration by the mycelium of Microdochium ?

A bit of a SWAG answer I know (Scientific wild ass guess - copyright Dr James Beard)

General Weather Situation

So as discussed above, we have a change in the weather dynamic coming up this week but before we do we have one more Atlantic low pressure system due to push into Ireland later this afternoon. Away from this approaching rain front, the U.K looks like starting off the week dry with only a run of showers pushing off The Mersey estuary into the north Midlands and some across the east of Scotland. Ireland will see rain pushing into the south west from late afternoon and this will cross the country during the evening, the Irish Sea later and move into The South West, West Wales and north west of England overnight. Temperatures will be into double figures and the wind will be strong and from the west.

Tuesday sees the bulk of that rain clearing Ireland and advancing in a concentrated band across the U.K, from west to east as dawn breaks. It will leave behind some showers across the west of Ireland and along western coasts of the U.K. This band of rain across England and Scotland will move quickly eastwards so hopefully by mid-morning Tuesday, it'll have cleared the eastern coast of England. It will be slowest to clear across The North East and eastern Scotland. Behind this rain they'll be a rash of showers feeding in from western coasts with some drier interludes. Remaining mild with temperatures up to 10°C for Ireland, Wales and England, a degree or two down on this across the south and east of Scotland with that rain and heavier cloud cover.

As that low pressure moves eastwards its trailing edge will drag down northerly winds so Wednesday sees cooler northerly winds come into the weather picture. These will knock down the temperature across all areas towards 6-7°C, so notably cooler. Wednesday is the change day as we see drier weather push in from the west as that high pressure builds to the west of Ireland. Some showers still lingering first thing on Wednesday, but it's a largely dry cool picture for all areas. Temperatures will drop markedly on Tuesday and Wednesday evenings close to a frost in places if skies clear.

Thursday will see a weak weather front cross the U.K and bring rain to Scotland overnight in the early hours of the day. This front will push rain down into the north west of England and move south and east, weakening as it does so. So a bit of a blip but away from the west of Scotland which will pick up the bulk of the rain associated with this front. Ireland should benefit from being closest to the strengthening high pressure so dry here on Thursday. Remaining cool with a changeable wind direction.

Closing out the week on Friday, we still see some unsettled weather across west and north west Scotland as an Atlantic low pressure pushed north by the high pressure ridge, crosses Scotland. Away from this northern interloper, Friday looks like being a nice dry day, remaining cool but plenty of sunshine and a drying wind as well, which I know will be welcomed by all.

The outlook for the weekend looks largely dry save for some rain that is projected to push rain into the west of Scotland through the course of Saturday. Away from this rain, the rest of the U.K and Ireland looks like having a largely dry and cool weekend with some sunshine and strong south westerly wind, which will help dry down of those saturated surfaces. Temperature-wise I expect 7-8°C as the norm for all areas during the day and 3-4°C at night.

Weather Outlook

So the GFS projection now extends up to and beyond Christmas and it presents an interesting weather dynamic on the run up to the 25th of December.

So we start next week with high pressure in charge as you can see from the GIF from tropicaltidbits.com.

That means cool and dry for the start of the week with a westerly wind but a noticeable change is underway as we can see from the GIF below.

During Tuesday we see a cold front push down from the north bringing rain, sleet and snow I think with it on the back of some strong and very chilly northerly winds. So that moisture will arrive first in Scotland on Tuesday and as the wind shifts to the north through next Tuesday it'll push further south. As you can see from the GIF above, the air is cold and for me that could well mean cold enough for snow. Nobody is shouting about this too much at the moment but watch this space.....Currently this spell of cold weather is projected to last until Thursday next week when milder, westerly weather may push in from the west and the threat of wintry showers will become more confined to easterly coasts.

By the end of next week we have that high pressure ridge back in place funnelling strong westerly winds into the weather picture, so hopefully that means dry, cool and sunny for most but always with a threat of moisture over the north and north west of the U.K. This could run some wintry showers down across the north of Ireland, Scotland and the north west of England on Christmas eve. Currently Christmas Day is looking windy from the west / north west with rain, sleet and possibly snow at elevation across Scotland with some of those showers drifting into northern England and further south. Too mild for snow I'd say though but plenty of time to change yet mind.

Agronomic Notes

Disease Pressure and Spray Windows

On the run up to Christmas the discussion is nearly always about getting a spray window, likely disease pressure and of course dew formation / removal.

Looking at the weather from now to Christmas, here is my take on it....

Spray Windows

Obviously this directly relates to your specific ground conditions after the recent rainfall at the start of this month, I can only comment on potential meteorological opportunities. With high pressure pushing in later this week, we will see a good potential spray window Thursday into Friday, extending to Tuesday next week. Now the caveat is for the north and north west which may see some rain pushing down from the west of Scotland on Thursday this week and it'll be this area that sees the breakdown first next week as that cold weather pushes down on Wednesday. Ireland looks to be similar to Wales and England, being closer to the high pressure this area will be sheltered by the high pressure ridge. So Thursday (ish) to Tuesday it is.....

Dew formation and disease pressure

Now this is qite a complicated dynamic for the next 5-7 days but here goes....

As the ridge of high pressure builds from Thursday, initially it'll be cool / cold as the wind direction is from the north west but as that high establishes over the weekend, it will pull up warmer air from the south and that's when I think we could see some aggressive disease activity and dew formation. The image below shows the temperature gradient associated with the high pressure on Friday and then on Sunday..

Note how the high pressure has picked up warmer air from the south over the weekend.

So for me, the highest disease pressure on the run up to Christmas will be over this coming weekend with mild, humid air and no doubt significant dew formation. As we move into next week, the pressure will continue through Monday and then begin to decrease as that wind swings round to the north on Tuesday.

Mitigation strategies

Now this is another tricky one to call because you may well already have some disease activity originating from the breakdown of the cold, frosty weather at the start of last week. For sure as commented upon earlier, we always tend to see more aggressive Microdochium activity following a frost. I know from research work conducted in my previous employment that Microdochium as a fungal species is able to grow rght down to 0°C and I think once the mycelium is inside the plant, it is protected from the effects of frost.

Quite why we see this increase in disease severity as the frost thaws is a difficult one to answer. It may just be a case of the fungus growing at a time when the grass plant is dormant so the effects of the fungal growth are clearer to see ?

It may as hinted above be due to the effect of the freeze-thaw cycle on the grass plant itself allowing fungal mycelium to develop into the leaf more quickly. Although this is possible, the speed of the apparent infection would suggest to me that the fungus is already in the plant before the frost and then grows quickly once the conditions change. For sure as the frost thaws it reverts to a moisture layer on the leaf itself, which we know in turn encourages disease growth.

The challenge before us is first to be able to get out to the greens to spray in some cases due to ground conditions and secondly to apply a spray that will be able to provide some degree of protection / dew mitigation. If you already have a fungicide on then I would concentrate on getting a dew control down before the weekend if you are indeed able. Applying both a fungicide and a dew control is a tricky proposition because you have to know that the surfactant will not affect the activity / working mechanism of the fungicide. In addition there's the risk of increased phytotixicity from applying this type of combination to a grass plant leaf.

This is when you are relying on your technical support to have done the trial work and research to answer the difficult questions arising from applying such a combination comes into play. In my latter years working in research, I successfully applied a dew control and a contact / protectant fungicide (that remained on the surface of the leaf) in just such these conditions. I'd love to name the specific products but that isn't possible. It can be done but you have to make sure your supplier has the necessary experience of such a tankmix to advise you confidentally. If in doubt, I think I'd apply a fungicide as my first choice and then try and follow up with a dew control later in the week. Looking at the weather next week, once we pick up those colder winds, disease pressure should relent with one last potential spray window possible at the end of next week.

If the forecast for the Christmas period is correct, the presence of a strong, drying westerly wind should mitigate both dew formation and high disease pressure. When and if that wind relents will be the weather combination to keep an eye out for between Christmas and New Year.

Fingers crossed and all the best for the coming week....

Mark Hunt