November 18th, 2024

Hi All,

It's been a couple of busy weeks since I last posted, first talking at Saltex, then last week at the excellent Scottish BIGGA conference and this week I am honoured to be invited to talk in my motherland, Denmark, at the Danish Greenkeepers Conference. Can't wait to experience that 5am Redeye, Ryanair experience !

This week our weather is finally on the change from the Omega blocking event that has positioned high pressure and humid, warm weather across the U.K & Ireland to a trough pattern vectoring in Arctic air, northerly winds, rain, sleet and snow, as the jet stream finally slinks south of the U.K. Quite a change when it was 16°C only a matter of days ago up north and now temperatures are in the minus region with snowfall.

Whenever I see this coming on the GFS, that track by 80's superlative beat masters, The Housemartins, turns up on my Spotify favourites. As the title suggests this track was written to describe the emotional transition from autumn to winter and it's a belter. Read about it here

With the weather turning colder, it is now more than ever that birds and other wildlife (my hedgehogs are still feeding at night) need our support. My Blackbirds are in particular very observant. As soon as they see me sat in the kitchen tapping away on the laptop, they land on the door handle and give me the evil eye, time for feeding !!!!!:)

A week ago, my ultra-reliable yardstick for the winter dropped onto the patio to feed on my morning offerings of suet sprinkles and mealworms. A pair of Grey Wagtails, later joined by a Pied Wagtail, appear when their insect supply gets tougher along the brooks and rivers of Market Harborough, stay for the winter and then depart in late February. They appeared on exactly the same date last year despite the difference between the two autumns.

General Weather Situation - 18-11-24

So as mentioned above, this week is all about winter with the usual uncertainty currently whether tonight's rain may or may not turn to snow across The Midlands (groan). That rain is currently vectoring across Ireland, it will cross The Irish Sea into Scotland, northern England and The Midlands later today and then edge eastwards and southwards overnight. The demarcation line between rain and snow is slipping southwards and eastwards as I type. It'll take till close of play tomorrow to depart the coast of south east England and whilst it does we could see more snow risk across South Wales on Tuesday morning. This snow risk will track eastwards across southern England tomorrow leaving us with a dry and cold end to Tuesday with a widespread frost. This looks to start a run of frosts that will continue through to Saturday morning.

After Monday / Tuesday's rain / sleet / snow event, it looks to be a predominantly dry and cold week, with a westerly wind which may pull in the odd shower to western Ireland and the Mersey estuary. That wind will turn more northerly further south as the low pressure tracks eastwards on Tuesday further reducing the wind chill temperature. Temperatures will be right down in the low single figures 2-4°C during the day and then -1°C to -4°C at night depending where you are located.

Now aside from the uncertainty from The Met Office today about quite where the snow event is / is not likely to occur across the south of the U.K, the next one will be Saturday when we see a deep Atlantic low pressure push in across Ireland and the southern half of the U.K. This low pressure has some tight isobars associated with it, so it'll be very windy and with that wind of course will be a lot of moisture / rain.

So as this milder, moist air hits the cold Arctic air on Saturday morning, I foresee the potential for some temporary snow, turning to rain soon after. As we progress through the weekend, milder air pushes up into the southern half of the U.K, whilst colder air will persist across Ireland, northern England and Scotland. On this note it could be 8-9°C by Sunday across the south.

Weather Outlook - 25-11-24

So after a taste of winter this week, what does next week hold for us weather-wise ?

Well it looks like next week we will start with a cooler high pressure in place over the U.K & Ireland. This normally means dry and settled which will be good after the rain over the weekend, however there is a potential fly in the ointment with the emergence of a BOB (Bay of Biscay) low pressure system from Tuesday to Thursday next week that could bring rain to the southern half of the U.K and Ireland. Thereafter the jet stream looks to take a hike upward (which is unusual for this time of year) and high pressure fills beneath it. So a cool and dry start to the week, a potentially wet mid-week interlude and then back to dry for the end of the week.(maybe)

Agronomic Notes

I have discussed this before but since we have just come through one of the longest periods of sustained disease pressure we have experienced I think it is worth reiterating.

I see a lot of discussion about fungicide efficiency on Facebook and the like, with the usual statements of "I have applied fungicide 'x' or 'y' but I am still seeing active disease".

It happens, and indeed through my time in this industry I have seen it oft-repeated. Even when we had 2 very strong 'contact' fungicides in Iprodione and Chlorothalonil, it still happened. (though chlorothalonil was strictly speaking a preventative protectant)

So what is going on ?

Well to answer that you have to understand the principle of modern-day fungicides. The term 'cide' is an ancient one and is connected to 'the act of killing / slaying, so putting the two together infers a killer of fungus. Whilst this may have been been true awhile back, modern-day fungicides that we are allowed to use tend to be more focussed on restricting the growth of the fungal pathogen population (there are of course differences in how they achieve this, sites of activity, etc). So what we are looking at in essence is an application of a product that restricts the growth of the fungus on the grass plant itself.

Now there is a contra-process to this occurring at the same time. This is the effect of the climatic drivers on fungal growth, i.e air temperature, humidity and plant leaf wetness (dew formation). All of these act as catalysts to fungal pathogen growth.

So what we are looking at is a kind of test of strength really between the ability of the fungicide to lower the growth rate of the pathogen (to a point below which it becomes non-symptomatic) vs. the ability of air temperature, humidity and plant leaf wetness to increase it.

If the effect of the climatic drivers is stronger than the effect of the fungicide, then we see symptoms appear (see diagram below and note the size of the arrows)

If the converse is true and the fungicide is more effective at controlling the growth rate of the pathogen than the climatic drivers are at promoting it, then we see control. (see image below and again note the size of the arrows)

Starting from the beginning of September and extending right through to last weekend, we have see periods of time when climatic drivers in the form of mild overnight temperatures, high humidity and long periods of plant leaf wetness promoted fungal growth faster than fungicide applications could control it. That is a fact.

Below is a chart of leaf wetness duration overnight vs. The Smith Kerns probability model from the beginning of September to the present day. I have highlighted 2 extended periods when the overnight plant leaf wetness and the Smith Kerns Dollar Spot Probability Model remained high on consecutive nights. The period in October ran for 13 nights in a row. I could have added the overnight humidity and air temperature to the same graph but it makes it difficult to see the pattern. Here it is clearer I think, anything above that blue line is high disease pressure and represents 7 hours or more of continuous plant leaf wetness, more than enough for Microdochium nivale (Fusarium if you want to call it by its old name). You can also see some nights where it has been over 10 hours (600 minutes) which is the acknowledged threshold for Dollar Spot (Clarireedia homeocarpa).

Finishing on a positive note, you can also see how the Smith Kerns has dropped off completely of late and with the forecast for this week predicting cold conditions, I think we will see an end to this current run. My only note of concern is the potential for a new high pressure building as we move into December.

Ok, that's me for this week, all the best and wrap up well in that chilly northern wind.

Mark Hunt