October 24th

That was some rainfall we had at the weekend !

I was in a boat fishing yesterday morning when we received 24mm over a very short period and I had to bail it out 3 times to stop it from causing a serious problem. Later during the early evening we picked up another chunk of heavy rain, courtesy of a big storm with lightning and thunder.

It was more reminiscent of a summer's storm with the energy it contained.

One minute everything was still, no wind, just the sound of approaching thunder, the next, the wind was howling through the trees (more leaves), we had torrential rain, thunder and lightning. The fact that there was enough heat energy to generate / seed that storm with updrafts at the end of October is amazing but then when you consider we are mid-high teens every day (and most nights) currently and due to go higher this week, you can see why...

As suggested in last week's blog, the prospect of an unerringly warm Halloween is on the cards as a heat plume pushes up warm and humid air this week. It's likely to drive more disease pressure and of course with the grass growth we are getting currently, it will shorten the longevity of treatments to counteract it. I'll be looking at this later in the blog.

Meanwhile onto this week's weather.....

This is the feature that will shape our weather this week ; a heat plume from Africa !

It has two profound effects on our weather this week ; The first is the more obvious one, warm day and night temperatures. The second is that this developing warm air front will push the rain that's coming in from The Atlantic north, so it'll miss the southern half of the U.K and fall across Ireland, Wales, northern England and Scotland.

This plume is caused by a profound Omega block in the jet stream which is shown below in the graphic from Netweather.tv ;

The Met Office have a great video on Youtube explaining blocking patterns in the jet stream, you can view it here.

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General Weather Situation - w/c 24th October, 2022

So for this week, we start off mild and unsettled with plenty of could cover and showers moving across the U.K and Ireland through the course of Monday, accompanied by a strengthening south westerly wind and temperatures in the mid to high teens. Tuesday evening sees the first heavy rain front push across Ireland and currently it is projected to affect the eastern side of Ireland and western side of Wales before moving north and east into northern England overnight into Wednesday. Away from this rain, the southern half of the U.K looks to have a mid / very mild weather week with some sunshine, the odd shower pushing through mid-week and a drying south westerly wind. As the heat plume develops, the wind will become more southerly and the temperature will rise to the high teens and possibly nudging towards 20°C across the south of England !

It won't be totally dry though because on Thursday a new rain front will push heavy rain into the south west of Ireland and this will move eastwards overnight into Wales and push across the U.K during the course of Friday. There's a suggestion this rain will intensify as it does so across the south east of England on Friday evening. It'll also be heavy across northern England and Scotland later on Friday. Despite the rain, it'll be very mild, strangely so I'd say.

The weekend will continue the mid / warm theme, accompanied by those mild southerly winds meaning mid to high teen daytime temperatures and remaining in double figures during the night. On Saturday a rain front is projected to push up into southern England and build across the south and head northwards during the second part of the day bringing heavy rain as it does so, finishing up in Scotland later the same day. Ireland looks to be drier on Saturday but wetter on Sunday as more rain and mild weather pushes into the south west of the country. Sunday looks to be the better day for England, Wales and Scotland with drier conditions and continuing very mild.

Weather Outlook

The animated GIF's courtesy of tropicaltidbits.com tell the story of next week's weather nicely. So it looks like the heat plume / blocking pattern will be in place as we start next week pushing most (but not all) of the rain west and north for Monday and Tuesday and maintaining those overly mild for the time of year, day and night time temperatures.

As we get to Wednesday, that high begins to be pushed south and east by a strong Atlantic low. This brings with it more rain for Ireland on Wednesday accompanied by a change in the wind direction to south west and an increase in wind strength to gale as those isobars pack closely together. This rain quickly moves across The Irish Sea into the U.K later on Wednesday and brings an unsettled wet and windy theme to the U.K, along with slightly cooler temperatures, but remaining mild I'd say. More rain follows across Ireland and the U.K later on next week and through the weekend before some respite potentially appears thereafter in the shape of a high pressure system.

Agronomic Notes

Rainfall vs. E.T update

Last week, I summarised some month-to-date rainfall and E.T stats to show how we were still dry in some areas and in desperate need of rain. I promised to update this week to see how the situation changed with the wet weather at the end of last week and over the weekend.

So the bottom graph shows how all locations are now in a surplus situation with some quite considerable transitions. Guildford for example, added just shy of 72 mm of rainfall last week and is now showing a healthy surplus vs. E.T. On the flipside, Scarborough by comparison only added 20mm so is only just in a surplus situation. I'll revisit next week but I expect the north and west locations to show the greatest change as that's the way most of the rainfall is heading.

Mild temperatures is both a blessing and a curse.....

The unseasonably mild weather is in some ways both a blessing and a curse because it brings with it more rain which we definitely need, but also more disease pressure, less spray days and rapid growth for the time of year.

Below is the daily growth potential from 4 locations across the U.K and Ireland and you can see that for the Irish and 2 English locations, we are sitting at over 80% (0.8) of optimum growth as we speak. That's normally the daily level of growth we see from May onwards !!!

Fungicide Longevity

In an earlier incarnation, I did a lot of work plotting disease incidence against fungicide longevity and grass growth rates. I worked out that a cumulative growth potential of around 10 was a pretty good marker for the longevity you can expect to get from a systemic fungicide. Now there's a lot of variables associated with fungicide longevity.

One of the main ones is how well it is retained in modern day rootzones.

STERF (Scandinavian Turfgrass and Environment Research Foundation) did some great research on this back in 2018/19 looking at how mobile certain fungicides were in a rootzone, how well they bound to organic matter and how much was lost through leachate (and therefore potentially contaminating water courses)

You can read it here

They also do some very interesting and brilliant research, read about what they're up to here

You can imagine when you have applied a fungicide and we get daily rain events like the one I highlighted at the start of this blog, some of this may end up being lost to the environment unless you have used a rainfast agent on application or the formulation already includes one. STERF found considerable variability in the leaching potential of fungicide actives. If you're applying a fungicide at this time of year, I would make sure you add in an approved adjuvant to retain it on the leaf and prevent run off. (NB - Some fungicides already have good rainfast agents within the formulation, so check before application)

Assuming you have good uptake and minimal loss after application, how long is a systemic fungicide lasting at the moment ?

It is a complicated question because I think it depends on the A.I loading, it's mode of uptake and efficacy on Microdochium nivale.

For example, if you're applying a contact protectant that stays on the leaf surface and isn't absorbed into the plant, then it probably isn't going to last longer than 5-7 days maximum when the daily G.P is where it is currently.

If you are applying a systemic fungicide with good activity against Microdochium then the graph below shows how long it should be lasting (assuming you applied on 01-10-2022 for example) ;

So assuming you applied at the beginning of October, the chart above shows the estimated longevity of an effective systemic fungicide.

Location Longevity

Shannon 17 days

Dumbarton 22 days

Scarborough 19 days

Guildford 18 days

So dependent on your location, it would be anywhere from 18 - 22 days.....not bad considering, but that is only because we had a cooler period mid-month. If you applied after this period and take into account we are averaging a daily G.P of 0.75 since at some locations, then your longevity will be closer to 13 days, less than 2 weeks.....

Should we be extending PGR applications into the autumn ?

I am a great believer in binning the calendar when it comes to turfgrass management and reacting to whatever Mother Nature, with her increasingly fickle ways, throws at us.

So in considering this question I think we have to take into account that our autumn season has changed radically in terms of temperature and the trend appears to be continuing. When you are faced with spending a lot of money on an amenity-registered fungicide , would the use of a PGR before or after application not be a good idea ?

It is a tricky question because applying the two together can cause issues in terms of phytotoxicity with some A.I's. You also have to consider if you apply a PGR and slow down the growth rate of the plant, do you affect the uptake speed of the fungicide ?

On the flipside, if the plant is regulated, you are removing less clippings, so more of the A.I stays in place, even in periods of unusually high growth. I also think as light levels decrease in the autumn with poorer weather and shorter days, the growth habit during these periods of fast growth isn't a good one. With low light, I think the plant stretches up towards the light, increasing the distance between the nodes and producing a thinner cell wall as a result. A bit like if you left a plant on the windowsill in a dimly-lit room. It grows leggy. A thinner cell wall makes it easier for a disease pathogen to penetrate and develop.

So there are lots of factors to consider.

What is the correct conclusion ?

Well I don't know to be honest, I have some thoughts on the matter and as Dr James Beard used to say, it's probably worthy of a 'SWAG' answer. That is a Scientifically Wild Assed Guess :)

On balance, I think there is a case for extending PGR usage into the autumn to help manage the almost unnatural type of growth we are experiencing. I probably wouldn't combine them in the same spray application unless the manufacturer / supplier gave the mix the thumbs up AND showed me some hard and fast data that the combination is a synergistic one rather than representing an increased risk of phytotoxicity and poorer fungicidal performance. Remember also that as we get into applying dew controls, a more regulated plant will be a benefit here as well :)

I'd be really interested in your feedback so if you are already doing this and happy to share the information, so please don't hesitate to contact me on markh@weatherstations.co.uk.

Come and say hello

Finally, next week I will be at Saltex with Peter Palmer, my esteemed colleague, to talk about all things Davis weather station and reporting software, so if you're up, please pop along to stand CO97 and have a chat, it would be great to see you 👍

All the best

Mark Hunt